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 The sentential theory involves no explicit commitment to abstract propositions. But propositions can still enter in the analysis of what it is for a given sentence to mean that such and such is the case. Thus, it is a mistake to suppose that a sentential approach to belief automatically repudiates propositions.
 There are four min dominant versions of the sentential theory usually adduce as motivating their view. To begin with. It is that the view that the mind is a computer is one that has considerable empirical support from cognitive psychology. The sentential theory, then. Is an empirically plausible theory, one that supplies a mechanism for the relation that propositionalists take to obtain between minds and propositions? The mechanism id mediation by inner sentences.
 Secondly, the sentential theory offers a straightforward explanation for the parallels that obtain between the objects and contents of speech acts and the objects  of contents of belief. For example, I may say that I believe. Furthermore, the object of believing like the object of saying, can have semantic properties. We may say, for  example.
What Jones believes is true
and:
What Jones believes entails what Smith believes
One plausible hypothesis, then, is that the object of belief is the same sort of entity as what is uttered in speech acts (or, what is written down).
 The sentential theory also seems supported by the argument, that the ability to think certain thoughts appears intrinsically connected with the ability to think certain others. For example, the ability to think that Walter hits Mary goes hand in hand that Mary hits Walter, but not with the ability to think that Toronto is overcrowded. Why is this? The ability to produce or understand certain sentences is intrinsically connected with the ability to produce or understand certain others. For example, there are no native speakers of English who know how to say ‘Walter hits Mary’ but who do not know how to say ‘Mary hits Walter’. Similarly, there are no native speakers who understand the former sentence but not the latter. These facts are easily explained if sentences have a syntactic and semantic structure. But if sentences are taken to be atomic, these facts are a complete mystery. What is true for sentences is true also for thoughts. Thinking thoughts involves manipulating representations with a propositional content have a semantic and syntactic structure like that of sentences, it is no accident that one who is able to think that Walter hits Mary is thereby also able to think that Mary hits Walter. Furthermore, it is no accident that one who can think these thoughts need not thereby be able to think thoughts having different components - for example, the thought that Toronto is overcrowded. And what goes here for thought goes for belief and the other propositional attitudes.
Consider the inference from:
Rufus believes that the round object ahead is brown
And:
The round object ahead is the coin Rupert dropped
To:
Rufus believes that the coin Rupert dropped is brown
This inference is strictly parallel to the inference from:
Rufus uttered the sentence ‘The round object ahead is brown
And the round object ahead is the coin Rupert dropped to:
Rufus uttered the sentence ‘The coin Rupert dropped is brown’
If the immediate object of belief are sentences, we should ‘expect’ the former inference to be invalid just as the latter is.
 Another motivating factor is the thought that, since the pattern of causal interactions among beliefs mirrors various inferential relations among the sentences that entail relations among the sentences that are ordinarily used to specify the object of beliefs have logical form. For example, corresponding to the inference from:
All dogs make good pets
And:
All of Jane’s animals are dogs
To:
All of Jane’s animals make good pets
We have the fact that, if Walter believes that all dogs make good pets and he later comes to believe that all of Jane’s animals are dogs, he will, in all likelihood, be caused to believe that all of Jane’s animals make good pets. Generalizing, we can say that a belief of the form
All F’s are G’s
Together with a belief of the form
All G’s are H’s
Typically causes a belief of the form
All F’s are H’s
This generalization concerns belief alone. But there are also, generalizations linking belief and desire. For example, a desire of the form:
Do A.
Together with a belief of the form:
In order to do A, it is necessary to do B
Typically generates a desire of the form:
Do B.
Now these generalizations categorize beliefs and desires according to the logical form of their object. They therefore require that the object have logical forms. But the primary possessors of logical form are sentences. Hence  the (immediate) objects of beliefs and desires are themselves sentences.
 Advocates of the propositional theory sometimes object to the sentential approach on the grounds that it is chauvinistic. Maybe our beliefs are represented in our heads in the form of sentences in a special mental language, but why should all beliefs necessarily be so represented in all possible creatures? For example, could not belief tokens the form of graphs, maps, pictures, or some other form dissimilar to any of our public forms of representation?
 This objection is based on a misunderstanding. The sentential theory is not normally presented as an analysis of the essence of belief, of what is common to all actual and possible believers in virtue of which they have beliefs. So, it has nothing to say about the beliefs of angels, say, or other possible believers. Rather it is a theory of how belief is actually realized in us.
 There is another important class of beliefs, however. These are standardly attributed using predicates of the form, believes of ‘x’ that it is ‘F’. Beliefs of this sort are called ‘de re beliefs’. Consider, for example, my believing of the building I am facing that it is an imposing structure. This is a belief with respect to a particular building, however, that building is described. Suppose, for example, that building is St Paul’s Cathedral. Then, in believing of the building I am thereby believing of St Paul’s that it is an imposing structure. So, for a belief to be ‘de re’ with respect to some object ‘θ’ which the belief is about. By contrast, if I simply believe that the building I am facing is imposing - this is the ‘de dicto’ case - I need not believe that the building I am facing is St Paul’s. moreover, I t is not a condition of my having the belief that the building I am facing is before me. I might, for example, be under the influence of some drug, which has caused me to hallucinate a large building.
 De re beliefs, then, are beliefs held with respect to particular things or people, however described that they have such and such properties. On the propositional theory, such beliefs are often taken to require that the given thing or person itself believing of Smith that he is dishonest is a matter of standing in the belief relation to the proposition that Smith is dishonest, where this proposition is a complex entity having the person, Smith as one of its components.
 The sentential theory can account for ‘de re’ belief in a similar fashion. The assumption now is that the inner sentence is a singular one (consisting in the simplest case of a name concatenated with a predicate). This sentence has, as its meaning, a proposition which meets the above requirement (assuming a propositional approach to sentence meanings).
 Of the two theories the sentential view probably has the wider support in philosophy today. However, as earlier, comments should have made clear, the two theories are not diametrically opposed to one another. For the sentential theory, unlike the propositional view of belief. Moreover, its advocates are not necessarily against the introduction of abstract propositions.
 There is one further feature worth commenting upon that is common to both the theories. This is their acceptance of the relational character of belief. The primary reason for tasking belief to be relational is syntactic objects. For example:
Jones believes that gorillas are more intelligent than chimpanzees
Entails:
There is something Jones believes.
Not all philosophers accept that existential generalizations like this one should be taken at face value as indicating a metaphysical commitment to some entity which is the believed object. However, unless some strong argument can be given which show that this case is anomalous, it is surely reasonable to existential generalization, and hence to grant that there really are objects in which we are related in belief.
 The hypothesis especially associated with Fodor, that mental processing occurs in a language different from one’s ordinary native language, but underlying and explaining our competence with it. The idea is a development of the Chomskyan notion of an innate universal grammar. It is a way of drawing the analogy between the workings of the brain or mind and those of a standard computer, since computer programs are linguistically complex sets of instruments whose execution explains the surface behaviour of the computer. As an explanation of ordinary language learning and competence the hypothesis has not found universal favour. It apparently only explains ordinary representational powers by invoking innate things of the same sort, and it invites the image of the learning infant translating the language surrounding it back into an innate language whose own powers are a mysterious biological given.
 Thought, in having contents, possess semantic properties. The syntax/semantic distinctions seem straightforward, but there are deep issues in linguistics and the philosophy of language tying in wait to make things more complex. First of all, though syntax is a matter of form, there are many possible levels of such form. Thus, knowing that a sentence is of the subject-predicate sort is a fairly sophisticated level of formal description, one must know something about grammatical categories to appreciate it. Consider ‘The cat is on the mat’, whenas of saying that it contains 16 letters and 5 spaces, or that it is composed of certain kinds of black-on-white shapes are descriptively no less formal, though they can be appreciated without any background grammatical knowledge.
 However, the complications really multiply in respect of semantics. It is one thing to say that the semantics of a sentence is its meaning, it is another to say what meaning is, or even to say how one would go about describing the meaning of words or sentences. Is it enough to say that the sentence ‘The cat is on the mat’ expresses the fact that the cat is on the mat? On the one hand, this seems uninformative - imagine it was the sole explanation of the meaning of this sentence. On the other hand, it is not clear how to understand ‘expresses the fact that’.
 Exactly what form a theory of meaning should take, and what level of syntactical description is most appropriate to understanding language, are problems for linguistic and philosophers of language. But the notions of syntax and semantics also play an important part in philosophy of mind. This arises because it is widely maintained that words and sentences are not the only kinds of thing that have syntax and semantics: In one way or another these features have been claimed for mental phenomena such as beliefs and other propositional attitudes. The range of representational systems humans understand and regularly use is surprisingly large, in that distinguishes items that serve as representations from other objects or events. There has ben general agreement that the basic notion of a representation involves one thing’s ‘standing for’, ‘being about’, ‘referring to or denoting’ something else. Thus, there is a view known as the ‘language of thought’ theory which maintains that beliefs are syntactically characterized items in the mind/brain and that they are semantically evaluable. According to this account, wee can best explain, for example, Smith’s belief that snow is white as his having in his mind/brain a token of a language of thought sentence - a sentence with some kind of syntax - which has as a semantic value the appropriate relation to snow and whiteness. Also, many not committed to the idea of a language of thought would still believe there to be a semantics of attitude states. So, the very difficult issue of how to describe the semantical relations carried over from the philosophy of language to the philosophy of mind. It is often called the ‘problem of intentionality’, though this label covers other issues as well.
 Beliefs are true or false. If, as representationalism had it, beliefs are relations to mental representations, then beliefs must be relations to representations that have truth values among their semantic properties. Sentences, at least declaratives, are exactly the kind of representation that have truth values, this in virtue of denoting and attributing. So, if mental representations says, we could readily account for the truth valuation of mental representations.
 Beliefs serve a function within the mental economy. They play a central part in reasoning and thereby, contribute in the control or behaviour in various ways. This core notion of rationality in philosophy of mind thus concerns a cluster of personal identity conditions, that is, holistic coherence requirements upon the system of elements comprising a person’s mind. A person’s putative beliefs must mesh with the person’s desires and decisions, or else they cannot qualify as the individual’s beliefs. Similarly, mutatis mutandis, for desires, decisions, and so forth. This is ‘agent-constitutive rationality’ - that agents possess it is more than an empirical hypothesis. A related conception is epistemic or ‘normative rationality’: To be rational (that is, reasonable, well-founded, not subject to epistemic criticism), a belief or decision at least must cohere with the rest of a person’s cognitive system - for instance, in terms of logical consistency and application of valid inference procedures. Rationality constraints therefore, are key linkages among the cognitive states. The main issue is characterizing these types of mental coherence.
 Reason capitalizes on various semantic and evidential relations among antecedently held beliefs (and, perhaps other attitudes) to generate new beliefs to which subsequent behaviour might be tuned. Apparently, reasoning is a process that attempts to secure new true beliefs by exploiting old [true] beliefs. By the lights of representationalism, reasoning must be a process defined over mental representation. Sententialism tells us that the type of representation in play in reasoning is most likely sensational - even if mental -, representations. Possibly, in reasoning mental representations stand to one another just as do public sentences in valid formal derivation. Reasoning would then preserve truth of belief by being the manipulation of truth-valued sentential representations according to rules so selectively sensitive to the syntactic properties of the representations as to respect and preserve their semantic properties. The sententialists hypothesis is thus that reasoning is formal inference: It is a process tuned primarily to the structure of mental sentences. Reasoners, then, are things very much like classically programmed computers.
 Would that the story could be so tidily told. Arguably we have infinitely many beliefs. Yet, certainly the finitude of the brain or relevant representational devices defies an infinity corresponding representation. So preserving sententialism requires disavowing the apparent infinitude of beliefs between (finitely many) actual beliefs - these being relations to actual Mentalese sentences - and (infinitely many) dispositional beliefs - these being the unactualized but potential consequences of their actual counter-parts. But this distinction in hand, the mind - as a sentential processor - is able so elegantly to manage and manipulate its actual beliefs so as regularly to produce the new beliefs rationally demanded of it in response to detectable environmental fluctuations. This and other related matters lead to notoriously difficult research problems whose solution certainty bears on or upon the plausibility of the language of thought. The sententialists must admit that if these problems finally prove intractable, then whatever warrant sententialists might otherwise have had, will have evaporated. But this aside, there are additional reasons in abductive support of sententialism.
 Nevertheless, representationalism is launched by the assumption that psychological states are relational, that being in a psychological state minimally involves being related to something. But, perhaps, psychological states are not at all relational. Might not the logical form of Peter Abelard (1078-1142), a controversial figure, he found his work condemned in 1121, and his scepticism about the legends of St Dionysius forced him to leave the Abbey of St Denis? Abelard wrote extensively on the problem of universals, probably adopting moderate ‘realism’, although he has sometimes been claimed as a ‘nominalist’. Also, writing commentaries on ‘Porphyry’ and other authorities. His ‘Scito te psum’ (‘know thyself’), is a treatise on ethics holding that sin consists entirely in contempt for the wishes of God, action is therefore less important than states of mind such as intention. Abelard’s contributions to logic have been the object of recent admiration. Abelard not a relation to anything but simply the monadic property of thinking in certain ways, however. Adverbialism begins by denying that expressions of psychological states are relational, infers that psychological states themselves are monadic and, thereby, opposes classical versions of representationalism, including sententialism.
 Adverbialism aspires to ontological simplicity in eschewing the existence of entities as theoretically recondite as mental representations. Nonetheless, it is hard pressed plausibly and simply to explain what in intuitivistically semantical yet, common to Abelard’s thoughts that are supposed monadic properties of thinking are, apparently no more mutually similar than either is to the property of thinking . It is, after all, only an orthographic accident and totally without significance that the predicates for the first two properties have portions of their spelling in common. Thus, unless Adverbialism allows for internally complete properties - in which case it seems to have no metaphysical advantage over its relational rival - it seems unable to meet the psychological facts.
 A semantic theory relates pieces of language to pieces of the world. We use language to talk about the world, and express our thoughts, which are also about the world. (The ‘aboutness’ of though it is oftentimes called ‘intentionality’). The relationship between talk, thought and the world, which is explored in the philosophy of language, the philosophy of mind and metaphysics.
 Thus, for example, we might try to give a philosophical account of some distinctions in reality - say, between objects and properties, or between particulars and universals - in terms of differences among words or in terms of differences in the realm of thought, provided that we already had some understanding of those linguistic or mental differences. Or, going the other way about, we might assume some account of the metaphysical differences, and use it in our philosophical words in the domains of talk or thought. There are also important questions of categorical priorities between philosophy of language and philosophy of mind. Indeed, any strategy for elucidating the concept of linguistic meaning will inevitably depend on our general view of the order of priority as between talk and thought.
 Suppose that we accept the intentionality of though, does this remove all force from the argument, it does not, if one accepts some connection between what we can conceive and what we can imagine. Whenever we imagine an object we imagine what it would be like perceived rom a certain viewpoint: We attempt to conceive of the object as it is independently of some possible perceptual perspective would have to be more abstract than a concrete imagination. As a physical object is an empirical object, with empirical properties, it might seem that thee was something peculiar about the idea that it possesses a mode of existence that could not be represented imaginistically, that is, in a form in which those empirical properties are actualized.
 The natural reply to this is that a good perspective on an object enables one to form a conception of the object as it is in itself. This is most simply represented by a clear view of a flat surface, which enables one to see it not merely from a perspective but as it is in its own plane. Our visual perception comes to be structured in three dimensions, so its having a perspective does not force us into having a merely abstract conception of the object in its own space, as it would do if vision were two dimensional and distance was only inferred.
 The most significant feature of thought is its ‘intentionality’ of ‘content’: In thinking , one thinks about certain things, and one thinks certain things of those things - one entertains propositions that stand for states of affairs. Nearly all the interesting properties of thoughts depend upon their content: Their being coherent or incoherent, disturbing or reassuring, revolutionary or banal, connected logically or illogically to other thoughts bother to talk prepared to recognize the intentionality of thought. So we are naturally curious about the nature of content as we want to understand what makes it possible, what constitutes it, what it stems from. To have a theory of thought is to have a theory of its content.
 Four issues have dominated recent thinking about the content of thought, each may be construed as a questions about what sequence of its so depending for not depending. These potential dependencies concern: (1)The world outside of the thinker himself (2) language (3) logical truth (4) consciousness. In each case the question is whether intentionality is essentially, or accidentally related to the items mentioned: Does it exist, that is, only by courtesy of the dependence of thought on the said items? And this question determines what the intrinsic nature of thought.
 Thoughts are obviously about things in the world, but it is a further question whether they could exist and have the content they do whether or not their putative objects themselves exist. Is what I think intrinsically dependent upon the world in which I happen to think it? This question was given impetus and definition by a thought experiment due to the American philosopher Hilary Putnam (1926-), concerning a planet called Twin-Earth. On Twin-Earth. Whom of which there live thinkers who are duplicate copies of us, in all internal respects but whose surrounding environment contain different kinds of natural objects, and so forth. The key point is that since it is not possible to individuate natural kinds, in that things are solely by reference to the way they strike the people who think about particular things, for which thinking about them cannot be a function simply of internal properties of the thinker. Thought content is relational in nature, whereby it is fixed by external facts as they bear upon the thinker. Much the same point can be made by considering repeated demonstrative reference to distinct particular objects: What I refer in when I say ‘that ‘bomb’, of different bombs, depends on or upon the particular bomb in font of me and cannot be deduced from what is going on inside me. Context contributes to content.
 Inspired by such examples, many philosophers have adopted an ‘externalist’ view of thought content: Thoughts are not autonomous states of the individual, capable of transcending the contingent facts of the surrounding surfaces inherent to the perceptions of our world. One is therefore not free to think whatever one likes, as it were, whether or not the world beyond cooperates in containing suitable referents for those thoughts. And this conclusion has generated a number of consequential questions. Can we know our thoughts with special authority, given that they are thus, hostage to external circumstances? How do thoughts cause other thoughts and behaviour, given that they are not identical with any internal stares we are in?
 To believe a proposition is to accept it as true, and it is relative to the objective of reaching truth that the rationalizing relations between contents are set for belief. They must be such that the truth of the premises makes likely the truth of the condition, making clear this justificatory link. Paradigmatically, the psychological states that provide an agent with reasons are intentional states of  individuation in terms of their propositional content, as such is the traditional emphasis that the reason-giving relation is a logical or conceptual link of bringing the nature of this conceptual representation for actions that provide intentional states other than beliefs.
 We might say, that the objective of desires is their own satisfaction. In the case of reason for acting therefore, we are looking for a relationship between the content and the agent’s intentional states and the description of the action which show that performing an action of that kind has some chance of promoting the desired goals. The presence of a reason for believing or acting does not necessarily make a rational for an agent to believe or act in that way. From the agent’s point of view, overall she may have other beliefs which provide conflicting evidence, or conflicting desires. To establish what is rational to believe or do in general, of what we needs to take into account principles for weighing competing beliefs and desires. Of course, we do not always believe what is rational or act in the light of what we judge best, e.g., as, cases of self-deception and weakness of will show this. However, a minimum of rationality must be present in the pattern of a person’s belief, desire, intentions, and actions before they can be regarded as an agent with intentional states at all.
 Nonetheless, for some writers the justificatory and explanatory tasks of reason-giving d simply coincide. The manifestation of rationality is seen as sufficient to reexplain or acts quite independently of questions regarding casual origin. Within this model the greater the degree of rationality we can detect, the ,more intelligible the sequence will be where there is a breakdown in rationality, as in cases of weakness of will or self-deception, as there is a corresponding breakdown in our ability to make the action/belief intelligible.
 Once, again, the justificatory and explanatory role of reason cannot simply be equated. To do so fails to distinguish cases where I have reasons for which I believe from which your innocence could be deduced but nonetheless, come to believe you are innocent because you have blue eyes. I my Have intentional states that give me altruistic reasons for giving to charity but nonetheless contribute our of a desire to earn someone’s good opinion: In both these cases, although my belief could be shown to be rational in the light of other beliefs, and my actions in the light of my altruistic states, neither of these rationalizing links could form part of a valid explanation of the phenomena concerned. Moreover, cases of weakness of will show that I can have sufficient reason for acting and yet fail to act, e.g., I continue to smoke although I judge it would be better to abstain. This suggests that the mere availability of reasoning, however good, in favour of an action cannot in itself be sufficient to explain why it occurred.
 The casual explanatory approach to reason-giving explanations also requires an account of the intentional content of our psychological states, which makes it possible for such content to be doing such work. It also provides a motivation for the reduction of intentional characteristics to extensional ones. In an attempt to fit such intentional causality into a fundamentally materialist world picture. The very nature of the reason-giving  relations, however, can be seen to render such reductive projects unrealizable. This, therefore, leaves intensional and non-intentional levels of description in such a way as to accommodate intentional causality, without either over-determination or a miraculous coincidence of prediction from within distinct casually explanatory frameworks.
 What has not been considered carefully enough, however, is the scope of the externalists thesis - whether it applies to all forms of thought all concepts. For unless this question can be answered affirmatively we cannot rule out the possibility that thought in general depends on there being some thought that is purely internally determined, so that the externally fixed thoughts are a secondary phenomenon. What about thoughts concerning one’s present sensory experience, or logical thoughts, or ethical thought? Could there, indeed, be a thinker for when internalism was generally correct? Is external individuation he rule or the exemption? And might it take different forms in different cases?
 Since words are also about things, it is natural to ask how their intentionality is connected to that of thoughts. Two views have been advocated: One view takes thought content to be self-subsisting relative to linguistic content: With the latter dependent upon the former, the other view takes thought content to be derivative upon linguistic content, so that there can be no thought content to be derivative upon linguistic content, so that there can be no thought without fundamental principles of language. Thus arise controversies about whether animals really think, being non-speakers, or computers really use language, being non-thinkers. All such questions depend critically upon what one is to mean by ‘language’. Some hold that spoken language is unnecessary for thought, but that there must be an inner language in order for thought to be possible: While others reject the very idea of an inner language, preferring to suspend thought from outer speech. However, it is not entirely clear what it amounts to, to assert (or deny) that there is n inner language of thought. If it means merely that concepts (thought-constituents) are structured in such a way as to be isomorophic with spoken language, then the claim is trivially true, given one natural assumption. But if it means that concepts just are ‘syntactic’, items orchestrated into strings of the same. Then the claim is acceptable only insofar as syntax is an adequate basis for meaning - which on the face of it, it is not. Concepts no doubt have combinatorial powers comparable to those of words, but the question is whether anything else can plausibly be meant by the hypothesis of an inner language.
 On the other hand, it appears undeniable that spoken language does not have autonomous intentionality, but instead derives its meaning from the thoughts of speakers - though language may augment one’s conceptual capacities. So thought cannot post-date spoken language. The truth seems to be that in human psychology speech and thought are interdependent in many ways, but that there is no conceptual necessity about this. The only ‘language’ on which thought essentially depends is that of the structured system of concepts itself: Thought indeed depends upon there being thought indeed depends upon there being isolable concepts that can join with others to produce complex propositions. But ths is merely to draw complete propositions. Nonetheless, ths is merely to draw attention to a property  any system of concepts must have: It is not to say what concepts are or how they succeed in moving between thoughts as they do. All in what is the same, appeals to language at this point are apt to founder on circularity, since words take on the powers of concepts only insofar as they express them. Thus, there seems little philosophical illumination to be got from making thought depend upon language.
 Least remains in the question that whether intentionality is dependent upon consciousness for its very existence, and if so why. Could our thoughts have the very content they now have if we were not to be conscious beings at all? Unfortunately, it is difficult to see how to mount an argument in either direction. On the one hand, it can hardly be an accident that our thoughts are conscious and that their content is reflected in the intrinsic condition of our state of consciousness: It is not  as if consciousness leaves off where thought content begins - as it does with, say, the neural basis of thought. Yet, on the other hand, it is by no means clear what it is about consciousness that links it to intentionality in this way. Much of the trouble stems from our exceedingly poor understanding of the nature of consciousness in general. Just as we cannot see how consciousness could arise from brain tissue (the mind-body problem), so we fail to grasp that manner in which conscious states bear meaning. Perhaps content is fixed by extra-conscious properties and relations and only subsequently shows up in consciousness, as various naturalistic reductive accounts would suggest: Or, perhaps, consciousness itself plays a more enabling role, allowing meaning to come into the world, hard as this may be to penetrate. In some ways the question is analogous to, say, the properties of pain: Is the aversive property of pain, causing avoidance behaviour and so forth, essentially independent of the conscious state of feeling pain, being possibly present without the feeling, or is it that pain could only have in aversive function in virtue of the conscious feelings? This is part of the more general question of the epiphenomenal character of conscious awareness, much as conscious awareness is just a dispensable accompaniment of some mental feature - such as content of causal power - or as it that consciousness is structurally involved in the very determination of the feature? It is only too easy to feel pulled in both directions on this question, neither alternative being utterly felicitous. Some theorists suspect that our uncertainty over such questions stems from a constitutional limitation to human understanding. We just cannot develop the necessary theoretical tools with which to provide answers to these questions: So we may not in principle be able to make any progress with the issue of whether thought depends upon consciousness and why. Certainly our present understanding falls far short of providing us with any clear route into the question.
 Another, but relevant question pertains of what is the relation between mind and physical reality? Well-established schools of thought give starkly opposing answers to this question. The French mathematician and founding  father of modern philosophy was René Descartes (1596-1650), insisted that mental phenomena are non-physical in nature. This view seems inviting because mental phenomena are indisputably different from everything else. Moreover, its safe to assume that all phenomena that are not of or relating to the mind have some objectively phenomenal descriptions that are essentially structured in the shaping of nature. So it may seem that the best way to explain how the mental differs from everything else is to hypothesize that mind is non-physical in nature.
 But that hypothesis is not the only way to explain how mind differs from everything else. Its also possible that mental phenomena are instead just a special case of physical phenomena: They would then have properties that no other physical phenomena have, but would still themselves be physical. This explanation requires that we specify what is special about mental phenomena which makes them different from everything else. But we must specify that, in any case, just in order to understand the nature of the mental. Characterizing  mental phenomena negatively, simply as not being physical, does little to help us understand what it is for something to be mental.
 In Descartes’ time, the issue between materialists and their opponents was framed in terms of substances. Materialists such as the English philosopher, mathematician and linguist Thomas Hobbes (1588-1679) and French philosopher and mathematician Pierre Gassendi (1592-1655) who maintained that people are physical systems with abilities that no other physical system have, therefore, are special kinds of physical substance. Descartes’ Dualism, by contrast, claimed that people consist of two distinct substances that interact causally: A physical body and a non-physical unextended substance. The traditional conception of substance, however, introduces extraneous issues, which have no bearing on whether mental phenomena are physical or non-physical. And in any case, even those who agree with Descartes that the mental is non-physical have today given up the idea that there are non-physical substances that people are physical organisms with two distinctive kinds of states: Physical stares such as standing and walking, and mental states such as thinking and feeling.
 Accordingly, the issue of whether the mental is physical or non-physical is no longer cast in terms of whether people, and other creatures that have the ability to tink and sense, are physical or non-physical substances. Rather, that question is put in terms of whether the distinctively mental states of thinking, sensing, and feeling are physical states or non-physical stares. The identity theory is the materialist thesis that every mental state is physical, that is, that every mental state is identical with some physical state.
 If mental states are identical with physical states, presumably the relevant physical states are various sorts of neural states: Our concept of metal states such as thinking, sensing, and feeling are of course, different from our concepts of neural states, of whatever sort. But that is no problem for the identity theory. As the Cambridge-born Australian philosopher J.J.C.  Smart (1920-)who first argued for the identity theory, emphasized the requisite identities do not depend on our concepts of mental states or the meaning of mental terms, for ‘a’ to be the meaning with ‘b’, ‘a’ and ‘b’ must have exactly the same properties, but the terms ‘a’ and ‘b’ need not mean the same. For our agreeing with Joseph Butler, in stating that everything is what it is and not another thing. The difficultly is to know when we have one thing and not two. A rule for telling this is a principle if ‘individuation’ or a criterion of identity for things of the kind in question. In logic, identity may be introduced as a primitive relational expression or defined via the identity of ‘indiscernibles’, and is known as ‘Leibniz’s law’.
 But a problem does seem to arise about the properties of mental states. Suppose pain is identical with a certain firing of c-fibres. Although a particular pain is the very same state as a neural firing, we identify that this state as a neural firing, we identify that state in two different ways, a pain and as a neural firing. The state will therefore have certain properties in virtue of which we identify it as a pain and those in virtue of which we identify it as a neural firing. The properties in virtue of which we identify it as a pain will be mental properties, whereas those in virtue of which we identify it as a neural firing will be physical properties. This has seemed to many to lead a kind of duality, at the level of the properties of mental states. Even if we reject a duality or dualism of physical organisms and take people simply to be physical organisms, those organisms still have both mental and physical stares. Similar ly, even if we identify those metal with certain physical states, those state will nonetheless, have both mental and physical properties. So, disallowing duality or dualism, with respect to substances and their states simply leads to its reappearances at the level of the properties of those states.
 Mental states such as ‘thought’ and ‘desire’, often called ‘propositional attitudes’ and have ‘content’ that can be described by ‘that’ clauses. For example, one can have a thought, or desire, that it will rain. These states are said to have intentional properties, or intentionality. Sensations, such as pain and sense impression, lack intentional content , and have instead qualitative properties of various sorts.
 However, the problem about mental properties for sensations, since the painful quality of pains and the red quality of visual sensation seem to be irretrievably non-physical. Even so, if mental states are all identical with physical states, these states appear to have properties that are not physical. And if mental states do actually have non-physical properties the identity of mental with physical states would not sustain a thoroughgoing mind-body materialism.
 The Australian philosopher J.J.C. Smarts reply to this challenge is that, despite initial appearances, the distinctive properties of sensation are neural as between being mental or physical: In the term Smart borrows from Gilbert Ryle (1900-76) the English philosopher and classicist), is that, they are topic neutral. My having a sensation of red consists in my being in state that is similar, in respects that wee need not specified, to something that occurs in me I am in the presence of certain stimuli. Because the respect of similarity is not specified, the property is neither distinctively mental nor is it distinctively physical. But everything is similar to everything else in some respect or other. So leaving the respect or other. So leaving the respect similarity unspecified makes this account too weak to capture the distinguishing properties of sensation.
 A more sophisticated reply to the difficultly of mental properties is due independently to the forthright Australian ‘materialist’ and together with J.J.C. Smart, that David Malet Armstrong, the leading Australian philosophers of the second half of the twentieth century. Armstrong defends an uncompromising scientific ‘materialism’, together with a ‘functionalist’ theory of mind (1968), and David Lewis (1941-2002), an American philosopher whose ‘Convention: A Philosophical Study’ (1969), rehabilitated the notion of ‘convention’, at the time regarded with deep suspicion both philosophers of language and by political theorists. ‘Counterfactuals’ (1973) introduced the now classic ‘possible worlds’ treatment of such statements. Both were to argue that for a state to be a particular sort of intentional characteristic casual relations to other particular occurrences. The properties in virtue of which we identify states as thoughts or sensations will still be neural as between being mental or physical, since anything can bear a causal relation to anything else. But causal connections have a better chance than
similarity in some unspecified aspect of sensation and thoughts.
 The causal theory is ingathering the view that the link between words and the world, whereby words mean what they do, is a causal link. The theory is aired in Kripke’s ‘Naming and Necessity’ for the special case of proper names. A plausible way of thinking o the link between the name ‘Plato’ and the philosophe r Plato is that there was an original naming of the philosopher with a term, which is itself an ancestor of the word we use, and a reference-preserving linkage causally responsible for our present use of the term. Even in this case, there are difficulties over what makes for a reference-preserving link, and extending the theory of other kinds of term, such as those designing ‘natural’ kinds, is not straightforward.
 Nonetheless, its misguided to try to construe the distinctive properties of mental states as being neural as between being mental or physical. To be neural regards being mental or physical is to be neither distinctively mental nor distinctively physical. But since thought and sensations are distinctively mental states, for a state to be a thought or a sensation is perforced for it to have some characteristically metal property. We inevitably lose the distinctively mental if we construe there properties as being neither mental nor physical.
 Not only is the topic-neutral construed misguided: The problem it was designed to solve is equally so. That problem stemmed from the idea that the mental must have some non-physical aspect. If not at the level of people or their mental states, then at the level of the distinctively mental properties of those states. A thorough discussion would take one deep into metaphysical and ontological issues, but, in the context of philosophy of mind, it is important to have some grasp of this notion. The best way to appreciate what is meant by a property is by contrast with  two others: Predicated and concept. Consider first the sentence: ‘Walter id bearded’. The word ‘Walter’ in this sentence is a bit of language - a name of some individual human being - and no one would be tempted to confuse the word with what it names. Consider now the expression ‘is bald’. This too is a bit of language - philosophers call it a ‘predicate’ - and it brings to our attention some property or feature which, if the sentence is true, is possessed by Walter. Understood in this way, a property is not itself linguistic though it is expressed, or conveyed by something that is, namely a predicate. What might be said is that a property is a contrasted just as sharply with any predicate we use to express it as the name ‘Walter’ is contrasted with the person himself. However, it is a matter of great controversy just what sort of ontological status should be accorded to properties. Many philosophers think that one should keep one’s ontological commitments to the minimum, and these philosophers - known as ‘nominalists’ would count only particular physical objects as ontologically suitable. But even if you are willing to accept properties and relations into your ontology, it still a further question whether you would count, e.g., belief as properties of person and/or relations between persons and belief contents. This sort of question about belief is ontological, and such questions figure widely in most areas of philosophy of mind. Even so, discussions of consciousness and action are often cast as debates about the ontological status of things as pains, sensations of colour, qualia and particular instances of action. Nevertheless, one could leave ‘dualism’ out of the characterization altogether by describing the view of as ‘anomalous monism’. This label - coined by Donald Herbert Davidson (1917-2003) the American philosopher, instigating mental and physical descriptions of persons, and the possibility of genuine explanation of events in terms of psychological properties. While at the sam time signalling a refusal to continence reduction, describing the mental as anomalous in respect of the physical just is a way of denying reducibility.
 But the idea that the understanding, is that of or relating to the mind is in some respect non-physical cannot be assumed without independent variabilities. Plainly, the distinctively mental properties of mental states are unlike any other properties we know about: Only mental states have properties that are at all like the quanlitive properties of sensations. And arguably nothing but mental stares have properties that are anything like the international properties of ‘thoughts’ and ‘desires’. Nonetheless, this does not show that these mental properties are not physical properties. Not all physical properties are like the standard cases: So, mental properties might still be special kinds of physical properties, in that, its question begging to assume otherwise. The doctrine that the mental properties of mental states are non-physical properties is simply an expression of the ‘Cartesian’ doctrine that the mind is automatically non-physical.
 To settle or not those mental properties are non-physical, we would need a positive account of what those properties are. Proposals and available that would account for intensional properties wholly in physical terms are that Daniel Dennett, (1942-), Dretske and Jerry Alan Fodor, if, perhaps, one of these will prove correct. Its been more difficult to gave a positive account for quantitative properties of sensation such that has lead to conclude that such properties will inevitably turn out to be non-physical. But its plainly unfounded to infer from the difficulty in explaining something to its being non-physical.
 It is sometimes held that properties should count as physical properties only if they can be defined using the terms of physics. This is far too restrictive, yet, nobody would hold that to reduce biology to physics, for example, we must define all biological properties using only terms that occur in physics. And even putting ‘reduction’ aside. If certain biological properties could not be so defined, that would no mean that those properties were in any way non-physical. The sense of ‘physical’ that is relevant must be broad enough to include not only biological properties, but also commonsense, macroscopic properties. Bodily stat es are controversially physical in the relevant way. So, we can recast the identity theory as asserting that  mental states are identical with bodily states.
 There are two ways to take the claim that every mental state is identical with some state. It might mean identity at the level of types, that is, that every mental state type is identical with some physical state type. Such type identity would hold if all the instances of a particular type of mental state are also instances of a particular type identity theory.
 But the identity claim might instead mean only that every instance of a mental state is identical with an instance of a bodily state of some type or other. On this construal, the various types of mental state would not have a correspond to types of bodily stare: Instances of a single mental type might be identical with tokens of distinct bodily types. The weaker claim is known as the ‘token identity theory’.
 There is reason to doubt that the type identity theory is true. It is plausible that organisms of different species may share at least some type of mental state - say, pain - even if their anatomical and physiological differences are so great that they cannot share the relevant types of bodily state. No single bodily-state type would then correspond to these mental-state types. This possibility is called the ‘multiple realizablity’ of mental states. It is conceivable, of course, that biology will someday type physiological states in a way that corresponds tolerantly well with types of mental state, but there is no guarantee that, that will happen.
 Even if no physiological types correspond to types of mental state, the causal theory of Lewis and Armstrong would allow us to identify types of mental state with types described in other terms. On Lewis’s version of the theory, mental states in whatever states occupy the casual roles specified by all our commonsense psychological platitude, taken together. The various types of mental roles thus specified: Mental-state tokens occupy the causal role that defines that type. These causal roles involve causal ties to behaviour and stimuli and to other states that occupy these casual roles. Such a theory, which define mental-state types in terms of causal roles, is oftentimes called ‘functionalism’.
 One could imagine that the individual states that occupy the relevant causal roles turn out to be bodily states, for example they might instead be states of an Cartesian unextended substance. But it is over-whelming like that the states that do occupy those casual roles are all tokens of bodily-state types. So the casual theory, together with this empirical likelihood, sustains at least the token identity theory. Moreover, this version of the causal theory bypasses the problematic idea that the mental properties of those states are neutral as between being mental or physical, since mental-state types are determined by our psychological platitudes.
 To defend the type identity theory as well, however, would require showing that all mental-state tokens that occupy a particular causal role also fall under a single physiological type. Lewis (1980) expects substantial uniformity of physiological type across the token of each mental-state type, at least within particular populations of creatures. But if tokens of different physiological types do occupy the same causal role that would undermine the type identify theory, or at least make it relative to certain populations.
 Multiple realizablity is the possibility that mental-state types are instantiated by stress of distinct psychological types. It is an empirical matter whether that is actually the case. If it is, physical-state types don not correspond to mental-state types to mental-state types, and the type identity theory is false.
 But one might, wit h Hilary Putnam (1975), construe the type identity theory more strongly, as claiming that the mental properties that define the various types of mental state are identical with physical properties. And that is false even if the tokens of each mental-state type fall under a single physiological type: The property of occupying a particular causal role is plainly of occupying a particular causal role is plainly not identical with the property of belonging to a particular physiological type. On this construal, no empirical findings are needed to refute the type identical theory. But it is more reasonable to construe the type identity theory less strongly, as requiring the claim only that all tokens of a particular mental-state type fall under a single physiological type.
 Donald Davidson (1970) has used different considerations to argue that mental-state types correspond to no physiological types, but that the token identity theory is nonetheless correct. Plainly, mental and bodily events cause each other. Moreover, as Davidson reasonably holds, one event token can cause another only is that causal connection instantiates some explanatory law. But Davidson also insists that an event token belongs to a particular mental type only relative to certain background assumptions about meaning and ‘rationality’. Tokens of physical events by contrast, belonging to whatever physical type they do independently of any such background assumptions. Davidson infers that there can be no strict laws connecting physical and mental events. But if so, how can mental and bodily events cause each other?
 In the hands of Davidson, the status of intentional generalization is used to a somewhat different end. Such generalizations provide the constitutive principles of rationality which govern our attribution of intentional states to ourselves and others. He argues that such attributions are open to constant revision and retain a residual indeterminacy which render our intentional notions quite unsuitable for inclusion in strict causal laws. The Davidson argument, however, classification in to necessarily undermined process of interpretation. For the causal theorists, in contrast, they are akin to natural kind terms, generating casual explanatory generalizations, and subject to no other such terms.
 The casual explanatory approach to reason-giving explanations also requires an account of the intentional content of our psychological states, which makes it possible for such content to be doing such work. It also provides a motivation for reduction of intentional characteristics to extensional ones, in an attempt to fit intentional causality into fundamentally materialist world picture. The very nature of the reason-giving relation, however, can be seen to render such reductive projects unrealizable, therefore, this leaves casual theorists with the task of linking intentional and non-intentional levels of description in such a way as to accommodate intentional causality, without either over-determination or a miraculous coincidence of prediction from within distinct causally explanatory frameworks.
 The claim that every mental state is identical with some bodily state, might mean that every mental state type is identical with some physical stare type. Such type identify would hold if all the instances of a particular type of mental state are also instances of a particular type of bodily state. This is called the ‘type identity
theory’.
 Yet, the identity claim might instead mean only that every instance of a mental state is identical with an instance of a bodily state, of some type or other. On this construal, the various types of mental state would not have to correspond to types of bodily state: Instances of a single mental type might be identical with tokens of distinct bodily types. This weaker claim is known as the ‘token identity theory’.
 There is reason to doubt that the type identity theory is true. It is plausible that organisms of different species may share at least some types of mental stare - say, pain - even if their anatomical and physiological differences are so great that they cannot share the relevant types of bodily state. No single bodily-stare type would then correspond to these mental-state types. This possibility is called the multiple realization of mental states. It is conceivable, of course, that biology will someday type physiological states in a way that correspond tolerably well with types of mental state, but we can have no guarantee that this will happen.
 Even so, if no physiological types correspond to types of mental state, the causal theory of Lewis and Armstrong would allow us to identify types of mental state with types described in other terms. On Lewis’s version of the theory, mental stats are whatever states occupy the causal roles specified by all our common-sense psychological platitude, taken together. The various types of mental state correspond to the various causal roles thus specified: Mental-state tokens are of a particular mental type. If they occupy the causal role that defines that type. These causal roles involve causal ties to behaviour and stimuli and other stares that occupy these casual roles. Such a theory, which defines mental-state types in terms of causal roles, if often called ‘functionalism’.
 One could image that the individual states that occupy the relevant causal roles turn out not to be bodily states: For example they might instead be states of an Cartesian unextended substance. But it is overwhelming likely that the states that do occupy those causal roles are all tokens of bodily-state types. So that causal theory, together with this empirical likelihood, sustains at least the token identity theory. Moreover, this version of the casual theory bypasses the problematic idea hat the mental properties of those states are neural as between being mental or physical, since mental-state types are determined by our psychological platitudes.
 To defend the type identity theory as well, however, would require showing that all mental-state tokens that occupy a particular causal role also fall under a single physiological type. Lewis (1980) expects substantial uniformity of physiological type across the token of each mental-state type, at least within particular populations of creatures. But if tokens of different physiological types do occupy the same casual role that would undermine the type identity theory, or at least make it relative to certain populations.
 Multiple realizablity is the possibility that mental-state types are instantiated by states of distinct physiological types. It is an empirical matter whether that is actually the case. If it is, physical-state types do not correspond to mental-state types, and the type identity theory is false.
 But one might, with Hilary Putnam (1975), construe the type identity theory more strongly, as claiming that the mental properties that define the various types of mental state are identical with physical properties. And that is false even if the  tokens of each mental-state type fall under a single physiological type: The property of occupying a particular causal role is plainly not identical with the property of belonging to a particular physiological type. On this construal, no empirical findings are needed to refute the type identity theory. But it is more reasonable to construe the true identity theory less strongly, as requiring the claim only that all tokens of a particular mental-stare type fall under a single physiological type.
 Donald Davidson (1970) has used different considerations to argue that mental-state types correspond to no physiological types, but that the token identity theory is nonetheless correct. Plainly, mental and bodily events cause each other. Moreover, as Davidson reasonably holds, one event token can cause another only if that causal connection instantiates some explanatory law. But Davidson also insists that an event token belongs to a particular mental type only relative to certain background assumptions about meaning and rationality. Tokens of physical events, by contrast, belong to whatever physical type they do independently of any such background assumption. Davidson infers that there can be no strict laws connecting physical and mental events. But if so, how can mental and bodily events cause each other?
 One way of brining out the nature of this conceptual link is by the construction of reasoning, linking the agent’s reason-providing states with the states for which they provide reasons. This reasoning is easiest to reconstruct in the case of the reasons for belief where the contents of the reason-providing beliefs inductively or deductively support the content of the rationalized belief. For example, I believe that my colleague is in his room now, and my reasons are (1) he usually has a meeting in his room at 9:30 on Monday. To believe a proposition is to accept it as true: And it is relative to the objective of reaching truth that the rationalizing relations between contents are set for belief. They must be such that the truth of the premises makes likely the truth of the conclusion.
 In the case of reasons for action the premises of any reasoning are provided by intentional states other than beliefs. Classically, an agent has a reason to perform a certain kind of action when he has (a) a pro-attitude towards some end or objective and (b) as belief that an action of that kind will promote this end. The term pro-attitude derives from Davidson. It concludes ‘desires’, ‘wanting’, ‘urges’, ‘prompting’, and a great variety of moral views, aesthetic principles . . . It is common to use ‘desire’ as a generic term for such pro-attitudes. It is relative to the constitutive objectives of desire that the rationalizing links are established in the practical case. We might say that the objective of desire is their own satisfaction. In the case of reason for acting therefore, we are looking for a relationship between the contents of the agent’s intensional state and the description of the action which show the preforming an action of that kind has some chance of promoting the desired goals.
 The presence of a reason for believing or acting does not necessarily make it rational for an agent to believe or act in that way. From the agent’s point of view overall he may have other beliefs which provide conflicting evidence, or conflicting desires. To establish what is rational to believe or do overall, we would need to take into account principles for weighing competing beliefs and desires. Of course, we do not always believe what is rational, or act in the light of what we judge best, least of mention, in cases of self-deception and weakness of will show this, however, a minimum of rationality must be present in the pattern of a person’s belief, desires, intention and action before they can be regarded as an agent with intentional states at all.
 The causal explanatory approach to reason-giving explanations also requires an account of the intentional content of our psychological stares, which makes it possible for such content to be doing such work. It also provides a motivation for the reduction of intentional characteristics to extensional ones. In an attempt to fit such intentional causality into a fundamental materialists world picture. The very nature of the reason-giving relation, however, can be seen to render such reductive projects unrealizable. This, therefore, leaves causal theorists with the task of linking intentional ad non-intentional levels of description in such a way as to accommodate intentionality as the frameworks for casual explanations.
 Davidson’s solution relies on the fact that explanatory laws describe events in particular ways and a different description of the same events might not sustain the explanatory connection. So the impossibility of laws connecting mental and physical events means only that laws can connect physical events, described as such, with mental events, described as such. To interact causally, events must figure in explanatory laws. So each mental-event token that interacts causally with a bodily event can figure in a law only if that mental-event token can also be described in purely physical terms. The consideration that preclude laws connecting mental with physical events presumably show also that no physical types correspond to any mental-stare types. But since we can describe every mental-event token in physical terms that token will be identical with some physical-event token. This intriguing argument is difficult to evaluate, mainly because it is unclear exactly why background assumptions about meaning and rationality should preclude laws connecting events described in mental terms with those described physically.
 In order for causal interactions between mental and bodily events to fall under laws that describe events solely in physical terms, physically indistinguishable events must be mentally indistinguishable, though not necessarily the other way around. That relationship is known as ‘supervenience’ in this case, mental properties would be said to this case, mental properties would be said to supervene on physical properties. Jaegwon Kim (1984) has usefully explored such supervenience as a way to capture the relation between mental and physical.
 The Cartesian doctrine that the mental is in some way non-physical is so pervasive that even advocates of the identity theory have sometimes accepted it, at least tacitly. The idea that the mental is non-physical underlies, for example, the insistence by some identity theorists that mental properties are really neutral as between being mental or physical. To be neutral in this way, a property would have to be neutral as to whether it is mental at all. Only if one thought that being mental meant being non-physical would one hold that defending materialism required showing that ostensible mental properties are neutral as regards whether or not they are mental.
 But holding that mental properties are non-physical has cost that is usually not noticed. A phenomenon is mental only if it has some distinctive mental property. So, strictly speaking, a materialist who claims that mental properties are non-physical would have to conclude that no mental phenomena exist,. This is the ‘eliminative e materialist’ position advanced by the American philosopher and critic Richard McKay Rorty (1931-). According to Rorty, ‘mental’ and ‘physical’ are incompatible terms. Nothing can be both mental and physical, so metal states cannot be identical with bodily states. Rorty trace this incompatibility to our views about incompatibility terms because we regard as incorrigible reports of one’s own mental states, but he also arguers that we can imagine a people who describe themselves and each other using terms just like our mental vocabulary, except that those people take the reports made with their vocabulary to be incorrigible. Since Rorty takes a state to be a mental state in one’s reports about it are taken to be incorrigible, his imaginary people not ascribe mental states to themselves or each other. But the only difference between their language and ours is that we take as incorrigible certain reports which they do not. So their language has no less descriptive or explanatory power than ours. Rorty concludes that our mental vocabulary is idle, and that there are no distinctively mental phenomena.
 This argument hinges on building incorrectibility into the meaning of the term ‘mental’. If we do not, the way is open to interpret Rorty’s imaginary people as simply having a different theory of mind from ours, on which reports of one’s own mental states are corrigible. Their reports would thus be about mental states, as construed by their theory. Rorty’s thought experiment would then provide reason to conclude, not that our mental terminology is idle, but only that this alternative theory of mental phenomena is correct. His thought experiment would thus sustain the non-eliminativist view that mental sates are bodily states, whether Rorty’s argument supports identity theory, therefore, depends solely on whether or not one holds that the mental is in some way non-physical.
 Paul M. Churchland (1981) advances a different argument for eliminative materialism. According to Churchland, the common-sense conceptions of mental states contained in our present folk psychology, are, from a scientific point of view, radically defective. But we can expect that eventually a more sophisticated theoretical account will replace those folk-psychological conception, showing that mental phenomena, as described by current folk psychology, do not exist. Since that account would be integrated into the rest of science, we would have a thoroughgoing materialism treatment of all phenomena. So this version of eliminativist materialism,
unlike Rorty’s does not rely on assuming that the mental is non-physical.
 Nonetheless, even if current folk psychology is mistaken, that does not show that mental phenomena do not exist, but only that are not the way folk psychology describes them as being. We could conclude they do not exist only if the folk-psychological claims that turn out to be mistaken actually define what it is for a phenomena to be mental. Otherwise, the new theory would still be about mental phenomena, and would help show that they are identical with physical phenomena. Churchland’s argument, like Rorty’s, depend on a special way of defining the mental, which we need not adopt. Its likely that any argument will require some such definition, without which the argument would instead support the identity theory.
 Early identity theorists insisted that the identity between mental and bodily events was contingent, meaning simply that the relevant identity statements were not conceptual truths. This leaves open the question of whether such identities would be necessarily true on other construals of necessity.
 The American logician and philosopher Aaron Saul Kripke (1940-) has argued that such identities would have to be necessarily true if they were true at all. Some terms refer to things contingently, in that those terms would have referred to different things had circumstances been relevantly different. Kripke’s example is,’The first master General of the US’, which in a different situation, would have referred to somebody other than Benjamin Franklin. Kripke calls these terms non-rigid designators. Other terms refer to things necessarily, since no circumstances are
possible in which they would refer to anything else; there terms are rigid designators.
 In the terms ‘a’ and ‘b’ refer to the same thing and both determine the thing necessarily, the identity statement ‘a = b’ is necessarily true. Kripke maintains that the term ‘pain’ and the terms for the various brain states all determine the states they refer to necessarily: If be in any of these circumstances are possible in which these terms would refer to different things. So if pain were identical with some particular brain state, it would be necessarily identical with that state,. But be necessarily identical with that state, it would be necessarily identical with that state. But Kripke agues that pain cannot be necessarily identical with any brain state, since the tie between pain and brain states plainly seem contingent. He concludes that they
cannot be identical at all.
 This argument applies equally to the identity of types and tokens. Whenever the term ‘pain’ refers to a state, it refers to that state rigidly: Similarly with the various terms for bran states. So if an individual occurrence of pain were identical with an individual brain state, it would be necessarily identical, they cannot be identical at all.
 Kripke notes that our intuitivistic amplitude about whether an identity is contingent can mislead us. Heat is necessarily identical with mean molecular kinetic energy. No circumstances are possible in which they are not identical. Still it may at first sight appear that heat could have been identical with some other phenomenon. But it appears this way. Kripke argues, only because we pick out heat by sensation of heat, which bears only a contingent tie to mean molecular kinetic energy. It is the sensation of heat that actually seems to be connected contingently with mean molecular kinetic energy, not the physical molecular kinetic energy, not the physical
heat itself.
 Kripke insists, however, that such reasoning cannot disarm our intuitive sense that pain is connected only contingently with brain states,. That is, because for a state to be pain is necessarily for it to be felt as pain, unlike heat, in the case of pain there is no difference between the state itself and how that pain is felt, and
intuitivism about the one are perforced intuitivistically about the other.
 Kripke’s assumption about the term ‘pain’ is open to question. As Lewis notes, one need not hold that ‘pain’ determines the same state in all possible situations, indeed, the casual theory explicitly allows that it may not. And if it does not, it may be that pains and brain states are contingently identical. But there also a problem about a substantive assumption Kripke makes about the nature of pain, namely, that pains are necessarily felt as pains. First impressions notwithstanding, there is reason to think not. There are times when we are not aware of our pains, for example, when we have suitably distracted. So the relationship between pains and our being aware of them between pains and our being aware of them may be contingent after all, just as the relationship between physical heat and our sensations of heat is. And that would disarm the intuitive pinch that pain is connected only contingently with brain states.
 Kripke’s argument focus on pains and other sensations, which because they have qualitative properties, are frequently held to cause the greatest problems for the identity theory. The American moral and political theorist Thomas Nagel (1937-) who is centrally concerned with the nature of moral motivation and the possibility of ca rational theory of moral and political commitment, and has been a major stimulus to interests in realistic and Kantian approaches to these issues. At this time, Nagel (1974) traces the general difficulty for the identity theory to the consciousness of mental states. A mental state’s being conscious, he urges means that there is something its like to be in that state. And to understand that, we must adopt the point of view of the kind of creature that is in the state. But an account of something is objective, he insists. Only insofar as its independent of any particular type of point of view. Since consciousness is inextricably tied to points of view, no objective account of it is possible. And that means conscious states cannot be identical with bodily states.
 The viewpoint of a creature is cental to what that creature’s conscious states are like because different kinds of creatures have conscious states with different kinds of qualitative property.  Nonetheless, the qualitative properties of a creature’s conscious stats depend, in an objective way, on the creature’s perceptual apparatus. We cannot always predict what another creature’s conscious states are like, just as we cannot always extrapolate from microscopic to macroscopic properties, at least without having a suitable theory that covers those properties. But what a creature’s  conscious states are like depend in an objective way on its bodily endowment, which is itself objective. So these considerations give us no reason to think that what those conscious states are like is not also an objective matter.
 If a sensation is not conscious, there is nothing its like to have it. So Nagel’s idea that what its like ti have sensations is central to their nature suggests that sensations cannot occur without being conscious. And that in turn seems to threaten their objectivity. If sensations must be conscious perhaps, they have no nature independently of how we are aware of them, and thus no objective nature, indeed, its
only conscious sensations that seem to cause problems for the identity theory.
 Although pain has the general properties of a sensory experience. It has, in addition, features beyond sensation that make it both more complex and of interest to a range of people other than sensory physiologists. The most important distinguishing feature of pain is uts affective-motivational aspect. In contrast to most other sensations, the pain experience necessarily include a quality of unpleasantness and the wish for its immediate termination,. Thus pain is one of the major forces, along with pleasure, that can shape behaviour
 (1) ‘Pain’ refer to a subjective experience (the notion of subjectivity underlies one’s concept of oneself a subject of experience, distinguished, in the first place, from the objects of experience, and, latterly, from other subjects of experience as well. The idea of subjectivity, tied in a deep way to a notion of a point of view, is the realization that one is not only a different subject of experience from other subjects of experience but also that the world is experienced differently by different subjects of experience.) In addition, the other simple sensory properties of pain include intensity and duration. Location and intensity may vary with time.
 (2) In common with all somatic sensations, pain has the property of sensory quality. Quality is a compound property that distinguishes a specific typ of pain from non-painful sensations and from different types of pain. For example, aching and burning are different qualities, the quality of a pain is often described in terms of a stimulus that might elicit it (i.e., burning, pricking or tearing). These terms often convey the sense of penetration, intrusion and assault upon the body. The quality of a pain is in part determined by the temporal and spatial variation of its primary properties, e.g., a brief sharp throbbing pain that radiates into the wrist.
 (3) In addition to the intensity of the stimulus that elicits it, the intensity of perceived pain is influenced by powerful modifying factors. These factors include the attention, expectation and state of arousal of the subject. For example, when two stimuli are applied simultaneously at different sites on the body, one stimulus may enhance or suppress the sensation resulting from the other stimulus. The effect of one stimulus on the sensation evoked by a second stimulus depends on the proximity of the two stimulus and their relative intensities (e.g., biting one’s lip may case the pain of a sprained ankle). Another example is that identical noxious stimulus, when repeatedly applied at the same site, evoke pain sensations that progressively increase in intensity and area.
 (4) The experience of ain characteristically is experienced by human subjects as a desire to escape, to terminate the sensation. When the sensation is intense and/or prolonged or its duration uncertain, the experience includes emotional component is called the effective-motivational dimension of pain to distinguish it from the sensory-discriminative dimension.
 (5) The negative effect of pain confers upon it the power, along with pleasure, to shape behaviour. This motivational power assures pain a place of great and unique importance, relative to other sensations. Obviously, better understanding of learning , memory and the human personality requires a fuller understanding of pain. The reverse is also true. Thus, pain is a fascinating object of study not only foe neuroscientsts but for medical scientists, psychologists, philosophers and theologians.
 (6) As with all other sensory phenomena, pain has a cognitive-evaluation component. This component represents both an abstraction and synthesis of the sensory and affective dimensions. Thus you might be aware of a severe pain in your heel which forces you to stoop walking. The cognitive-evaluative aspect of pain may involve remembering how far you will have to walk and weighing the decision to endure the unpleasant sensation against not getting to work on time.
 This dimension of pain includes its meaning. In some situations the meaning of a pain is by far its most important dimension to the individual. For example, the development of even mild pain in a patient being treated for cancer may be terrifying and depressing if it is believed to signify recurrence of a malignant tumour.
 (7) The sensory, affective and evaluative dimensions of pain have lawful interrelationships. The example cited in (6) illustrate how affect can be closely tied to  meaning. In humans, psychological studies confirm that the affective dimension of pin can be powerfully reduced or increased by factors such as psychological set and personality traits or by manipulations such as hypnosis or distraction.
 (8) Duration is a critical factor that influences pain. Clinically, the persistence of pain is associated with profound changes in the affective and evaluative dimension of pain. Whereas acute pain (minutes to hours and days) is associated with restlessness, arousal, and fear, chronic pain (weeks to months and years) is associated with
resignation, depression, reduced activity and preoccupation with all bodily sensations.
 Nevertheless, the assumption that mental states are unvariably conscious, like the supposition that there are non-physical, is basic to the Cartesian view. But sensations do occur that are not conscious. A mental state’s being conscious consists in one’s being conscious of it in a way that is intuitively direct and unmediated, but as already noted, distraction often make us wholly unaware of our sensations. Sensations that are not conscious also occur in both subliminal perception and peripheral vision, as well ass in more esoteric context.
 Sensations can, moreover, have qualitative properties without being conscious. Qualitative properties are sometimes called ‘qualia’ with there implication that we must be conscious of them: But wee need not be bound by that term’s implications. Qualitative properties are simply those properties by means of which we distinguish among the various kinds of sensations when they are conscious. But a sensation’s being conscious makes no difference to what its distinguishing properties are, its being conscious consists simply in one’s being conscious of those properties in a suitable way. When a situation is not conscious its distinguishing properties seem to cause no difficulty for the identity theory. And since those properties are the same whether or not the sensation is conscious, there is nothing the identity theory. We would assume otherwise only if we held, with Nagel and Kripke, that sanctions must all be conscious.
 Perhaps multiple realizablity refutes the type identity theory, but there are ample arguments that support the token identity theory. Moreover, the arguments against the token theory seem all to rely on unfounded Cartesian assumptions about the nature of mental states. The doctrine that mental is in some way non-physical is straightforwardly question begging, and its simple not the case that all sensory stares are conscious. It is likely, therefore, that the identity theory, at least in that token version is correct.
 Its conveniences inbounded to Functional logic and mathematical function, also known a map or mapping, is a relation that associates members of one class ‘x’ with some unique member ‘y’ of another class ‘y’. The association is written as ‘y = f(x). The class ‘x’ is called the domain of the function, and whose domain includes all people, and whose range is the class of male parents. But the relation ’son of x’ is not a function, because a person can have more than one son. Since ‘x’ is a function of the perimeter of a circle, π x, it a function of its diameter ‘x’, and so forth. Functions may task sequences sch as < x1 . . . xn > as their arguments, in which case they may be thought of as associating a unique members of ‘y’ with any ordered n-tuple as argument. given the equation y = f(x1  . . . xn), x1 . . . xn are called the independent variable or value. Functions may be ‘many-one’, meaning that different members of ‘x’ may take the same member of ‘y’ as their value, or ‘one-one’, when to each member of ‘x’‘ their corresponds a distinct member of ‘y’. A function with domain ‘X’ and range ‘Y’ is also called a mapping from ‘x’ to ‘y’, written f X ➞ Y. If the function is such that
(1) if x, y ∈ X and f(x) = f(y) then x = y.
Then the function is an injection from X and Y . If also:
(2) if y ∈ Y, then (∃x)(x ∈ X & y f(x)).
Then the function is a bijection of ‘X’ and ‘Y’. A bijection is also known as a one-one correspondence. A bijection is both an injection and a subjection where a sirjection is any function whose domain is ‘x’ and whose range is the whole of ‘y’‘. Since functions are relations a function may be defined as a set of ‘ordered pairs’ < x, y > where ‘x’ is a member of ‘X’ and ‘y’ of ‘Y’.
 One of Frége’s logical insights was that a concept is analogous to a function, and a predicate analogous to the expression for a function (a functor) just as ‘the square root of ‘x’ takes us from one number to another, so ‘x’ is a philosopher’ refers to a function that takes us from persons to truth-values: True for values of ‘x’ who are philosophers, and false otherwise.
 An explanation of a phenomenon that cites the functional properties of contributing elements, than their physical or mechanical natures. The explanation of a computer’s behaviour that cites the software it is running is a functional explanation.
 In biology, the function of a feature of as organism is frequently defined as that role it players which has been responsible for its genetic success and evolution. Thus, although the brain weighs down the shoulders, this is not its function, for this is not why entities with brains are successful. A central question will be the unit whose ‘adaptation’ is in question: There may be persons, or their ‘genes’, or clusters of genes, or gene pools. It may be said that a person is a gene’s way of making another gene, just as a scholae is a library’s way of making another library. There also difficulties fortuitous roles that an adaptation may come to serve from its function proper.
 Profoundly, our impending of concern has taken on or upon the pretextual affiliation that makes apparent the evidential implicity as implicated in the philosophy of mind. Is that of ‘functionalism’, and to realize that functionalism is the modern successor to ‘behaviouralism?’. Its early advocates were Hilary Putnam, an American philosopher, who accordingly does not stand for a monolithic system or body of doctrine, and in so of himself concentrates upon the philosophy of science. And is not afraid of changing his mind, but in the latter part of his career his interests in the human sciences have become more prominent, his Reason, Truth and History (1981) marked a departure from scientific realism in favour of a subtle position that he calls ‘internal realism’, initially replaced to an ideal limit theory of truth, and apparently maintaining affinities with verification, but in subsequent work more closely aligned with ‘minimalism’. However, Putnam’s concern in the later period has largely been to deny any serious asymmetry between truth and knowledge as it is obtained in natural science, and so it is obtained in morals and even theology
 Also an advocate to the session of functionalism is Wilfrid Sellars (1912-89), the son of the philosopher Roy Wood Sellars (1880-1973), wherefor, Wilfrid’s early work represented a blend of ‘analytic philosophy’ with ‘logical positivism’, and together with others he founded the Journal Philosophical Studies (Readings in Philosophical Analysis, 1949, and Readings in Ethical Theory, 1952). Even so, his most influential paper ‘Empiricism and the Philosophy of Mind’, (1956), which was possibly the central text introducing ‘functionalism’ in the philosophy of mind, whereby the use of a sentence is to express an associated propositions, as a useful framework due to Sellars, divides use into three parts, there are ‘entry rules’ describing the kinds of situation justifying application of a term, as too, ‘exit rules’, for which of describing the practical consequences of accepting the application of the term, and ‘transformation rules’ taking us to other linguistic applications that themselves bear definite relations to the term.
 Its guiding principle is that we can define mental stares by a triplet of relations what typically causes them, and what effects they have on behaviour. The definition need not take the form of s simple analysis, but if we could write down the totality of axioms, or postulates, or platitudes that govern our theories about what things are apt to cause (for example) a belief state, what effects it would have on a variety of other mental states,. And what effects it is likely to have on behaviour, then we would have done all that is needed to make the state a proper theoretical notion. It would be implicitly defined by these theses.
 Functionalism is often compared with descriptions of a computer, since according to its mental descriptions correspond to a description of a machine in terms of software, that remains silent about the underlying hardware or ‘realization’ of the program the machine is running. The principal advantage of functionalism include its fit with the way we know of mental states both of ourselves and others, which is via their effects on behaviour and other mental states. As with behaviouralism. Critics change the structurally complex items that do not bear mental states might nevertheless imitate the functions that are cited. According to this criticism functionalism is too generous, and would count too many things as having minds. It is also queried whether functionalism is too parochial, able to see mental similarity only when there is causal similarity, when our actual practices of interpretation enable us to ascribe thoughts and desires to persons from our own. It may then seem as though beliefs and desires can be ‘variably realized’ in causal architecture, just as much as they can be in different neurophysiological states
 That an intelligent system, or mind, may fruitfully be thought of as the result of a number of sub-systems performing more simple tasks in co-ordination with each other. The sub-systems may be envisaged as homunculi, or small, relatively stupid agents. The archetype is a digital computer, where a battery of switches capable of only one response (on or off) can make up a machine that can play chess, write dictionaries, and so forth.
 The functionalist thinks of ‘mental states’ and events as causally mediating between a subject’s sensory inputs and that subject’s ensuing behaviour. Functionalism itself is the stronger doctrine that what makes a mental state the type of state it is - a pain, a smell of violets, a belief that koalas are dangerous - is the functional relations it bears to the subject’s perceptual stimuli, behavioural responses, and other mental states.
 Twentieth-century functionalism gained its credibility in an indirect way, by being perceived as affording the least objectionable solution of the mind-body problem.
 Disaffected from Cartesian dualism and from the ‘first-person’ perspective of introspective psychology, the behaviourists had claimed that there is nothing to the mind but the subject’s behaviour and dispositions to behave. Philosophically, the doctrine of behaviouralism is that mental states are ‘logical constructions out of dispositions to behaviour, or in other words, that describing the mental aspects of a person is a shorthand for describing the various dispositions to behaviour that the person possesses. The most influential work promoting this point of view was The Concept of Mind (1949), by Gilbert Ryle, an English philosopher and classicist, in which he urged behaviourism as the best defence against the Cartesian myth of the ‘ghost in the machine’. Yet, the extent of which Ludwig Wittgenstein writing the Philosophical Investigations, at the same time, intended to promote a behaviourist doctrine is subject to dispute. Like other ‘reductionist doctrines’ behaviourism fell foul of the difficulty of providing workable analyses, notably because of the ‘holist’ of the mental, or the fact that how a person behaves is not as function of one belief or one desire. The modification to take care of this turns behaviourism into its more popular modern successor, ‘functionalism’. For example, for Rudolf to be in pain is for Rudolf to be either behaving in a wincing groaning-and-favouring way or disposed to do so (in that he would so behave were something not keeping him from doing so): It is nothing about Rudolf’s putative inner life or any episode taking place within  him.
 Though behaviourism avoided a number of nasty objections to dualism (notably Descartes’ admitted problem of mind-body interaction), some theorist were uneasy: They felt that in its total repudiation of the inner, behaviourism was leaving out something real and important. U.T. Place spoke of an ‘intractable residue’ of conscious mental items that bear no clear relations to behaviour of any particular sort. And it seems perfectly possible for two people to differ psychologically despite total similarity of their actual and counter-factual behaviour, as in a Lockean case of ‘inverted spectrum’, for that matter, a creature might exhibit all the appropriate stimulus-response relations and lack mentation entirely.
 For such reasons, Place and Smart proposed a middle way, the ‘identity theory’, which allowed that at least some mental states and events are genuinely inner and genuinely episodic after all: They are not to be identified with outward behaviour or even with hypothetical dispositions to behave. But, contrary to dualism, the episodic mental items are not ghostly or non-physical either. Rather, they are neurophysiological. They are identical with states or events occurring in their owner’s central nervous systems. To be in pain is, for example, to have one’s c-fibres, or possibly a-fibres, firing. A happy synthesis: The dualists were wrong in thinking that mental items are non-physical but right in thinking them inner and episodic, the behaviourists were right in their ‘physicalism’ but wrong to repudiate inner mental episodes.
 However, Hilary Putnam (1960) and Jerry Fodor (1968) pointed out a presumptuous implication of the identity theory understood as a theory of types or kinds of mental items: That a mental type such as pain has always and everywhere the neurophysiological characterization initially assigned to it. For example, if the identity theorist intensified pain itself with the firing of c-fibres, it followed that a creature of any species (earthly or science-fiction) could be in pain only if that creature had c-fibres and they were firing. But such constraint on the biology of any being capable of feeling pain is both gratuitous and indefensible: Why should we suppose that any organism must be made of the same chemical materials as us in order to have what can be accurately recognized s pain? The identity theorist had overreached to the behaviourist’s difficulties and focussed too narrowly on the specifics of biological human’s actual inner states, and in so doing they had fallen into species chauvinism.
 Jerry Fodor and Hilary Putnam advocated the obvious correction: What was important`was not its being c-fibres (per se) that were firing, but their firing contributed to the role of the c-fibre could have been performed by any mechanistically suitable component part?: So long as that role was per performed, the psychology of the containing organism would have ben unaffected. Thus, to be in pain is not per se to have c-fibres that are firing. But merely to be in some state or other, of whatever biological description, that plays the same functional role as did the firing of c-fibres in the human beings. We may continue to maintain that pain ‘tokens’, individual instances of pain occurring in particular subjects at particular times, are strictly identical with particular  neurophysiological states of these subjects that happen to be playing the appropriate roles: This is the thesis of ‘token identity’ or ‘token physicalism’, but pain itself (the kind, universal or type) can be identified only with something more abstract: The causal or functional role that c-fibres share with their potential replacements or surrogates. Mental state-types are identified not with neurophysiological types but with more abstract functions to the organism’s inputs, outputs and other psychological states.
 Putnam compared mental states to the functional of ‘logical’ states of a computer. Just as a computer program can be realized or instantiated by any different hardware configurations, so can a psychological ‘program’ be realized by different organisms of various physicochemical composition, and that is why different physiological states of organisms of different species can realize one and the same mental state-type. Where an identity theorist’s type identification would take the form. To be in mental state of type ‘M’ is to be in the neurophysiological state of type ‘N’. Putnam’s machine functionalism (as we may call it) some physiological state or other that plays role ‘R’ in the relevant computer program (i.e., the program that at a suitable level or abstraction mediates the creature’s total outputs given total inputs and so serves as the creature’s global psychology) the physiological state ‘plays role ‘R’ in that it stands in a set of relations to physical inputs, outputs and other inner states that matches one-to-one the abstract input/output/logical-state relations codified in the computer program.
 The functionalist, then, mobilizes three distinct levels of description but applies them all to the same fundamental reality. A physical state-token is someone’s brain at a particular time has a neurophysiological description, but may also have a functional description relative to a machine program that the brain happens to be realizing, and it may further have a mental description if some everyday mental state is correctly type-identified with the functional category it exemplifies. And so there is after all a sense in which ‘the mental’ is distinct from ‘the physicals’: Though presumably there are no non-physical substances or stuff, and every mental token is itself entirely physical, mental characterization is not physical characterization, and the property of being a pain is not simply the property of being such-and-such a neural firing. Moreover, unlike behaviourism and the identity theory, functionalism doe not strictly entail that minds are physical: It might be true of non-physical minds, so long ass those minds realized the relevant programs.
 In a not accidental similar vein, behaviouralism in psychology has almost entirely given way to ‘cognitivism’. Cognitivism is roughly the view that (1) psychologists may and must advert to inner states and episodes in explaining behaviour, so long as the states and episodes are construed throughout as physical, and (2) human beings and other psychological organisms are best viewed as in some sense ‘information processing systems’. As cognitive psychology sets the agenda, its questions take the form, ‘How does this organism receive information through its sense-organs, process it in such a way as to result in intelligent behaviour’? The working language of cognitive psychology is highly congenial to the functionalists, for cognitivism thinks of human beings as systems of interconnected functional components, interacting with each other in an efficient and productive way.
 Meanwhile, researchers in computer science have pursued fruitful research programmes based on the idea of intelligent behaviour as the output of skilful information-processing given input. Artificial intelligence is, roughly, the project of getting computing machines to perform tasks that would usually be taken to demand human intelligence and judgement: Computers have achieved some modest successes, but a computer just is a machine that receives, interprets, processes, stores, manipulates and uses information, and artificial intelligence researchers think of it in just that way as they try to program intelligent behaviour. An artificial intelligence problem sees this as input, what must it do with that input nd what must it accordingly do with that input in order to be able to . . . [recognize, identify, sort, put together, predict, tell us, and so forth]  . . . ? And how, then, can we start it off knowing that and get it to do those things? So we may reasonably attribute such success as artificial intelligence has had to self-conscious reliance on the information-processing paradigm. And that in turn mutually encourages the functionalist idea that human intelligence and cognition generally are matters of computational information-processing.
 Machine functionalism supposed human brains may be described at each of three levels, the first two scientific and the third familiar to common sense: The biological specifically neurophysiological: The machine-program or computational, and the everyday mental or folk psychological. Psychologists would explain behaviour, characterized in everyday terms, by reference to stimuli and to intervening mental states such as belief and desires, type-identity the mental states with functional or computational states as they went. Such explanations would themselves presuppose nothing about neuroanatomy, since the relevant psychological/computational generalizations would hold regardless of what particular biochemistry might happen to be realizing the abstract program in question.
 Machine functionalism as described has more recently been challenged on each of a number of points that together motivate a specifically teleological notion of ‘function’:
  (1) the machine functionalist still conceived psychological explanation in the positivists’ terms of subsumption o data under wider ans wider universal laws. But Jerry Fodor, Dennett and Cummins (1983) have defended a competing picture of psychological explanation: According to which behavioural data are to be seen as manifestations of subject’s psychological capacities, and these capacities are to be explained by understanding the subject’s as systems of interconnected components. Each component is a ‘homunculus’, in that it is identified by reference to the function it performs, and the various homuncular components cooperate with each other in such a way as to produce overall behavioural responses in stimuli. The ‘homunculi’ are themselves broken down into sub-components whose functions and interactions are similarly used to explain the capacities of the subsystems they compose, and so, again, and again until the sub-sub . . . components are seen to be neuroanatomical structures. (An automobile works - locomotes - by having a fuel reservoir, a fuel line, a fuel injector, a combustion chamber, an ignition system, a transmission, and wheels that turn. If one wants to know how a fuel injector works, one will be told what parts are and how they work together to infuse oxygen into fuel , and so forth.) Nothing in this pattern of explanation corresponds to the subsumption of data under wider and wider universal generalizations, or to the positivists’ deductive-nomological model of explanation as formally valid derivation from such generalizations.
  (2) The machine functionalist treated functional ‘realization’, the relation between an individual physical organism and the abstract program it was said to instantiate, as a simple matter of one-to-one correspondence between the organism’s repertoire of physical stimuli, structural states and behaviour, on the one hand, and the program’s defining input/state/output or realization was seen to be literal, since virtually anything bears a one-to-one correlation of some sort to virtually anything else: ‘Realization’ in the sense of mere one-to-one correspondence is far to easily come by: For example, the profusion of microscopic events occurring in a sunlit pond (convection currents, biotic activity, or just molecular motion) undoubtedly yield some one-to-one correspondence or other to any psychology you like, but this should not establish that the pond is, or has, a mind. Some theorists have proposed to remedy this defect by imposing a teleological requirement on realization: A physical state of an organism will count as realizing only in the organism has genuine organic integrity and the state plays its functional role properly for the organism, in the teleological sense of ‘for’ and in the teleological sense of ‘function’ the state must do what it does as a matter of, so to speak, its biological purpose. This rules out our pond, since the and is not a single organism having convection currents or molecular motion as organs. (Machine functionalism took ‘function’‘ in its spare mathematical sense than in a genuine functional sense. The term ‘machine factional sense’ is tied to the original libertine conception of ‘realizing’, as so to impose a teleological restriction is to abandon machine functionalism).
  (3) Of the machine functionalist’s three levels of description, one is common-seismical and two are scientific, so we are offered a two-levelled picture of human psychobiology in the extreme. Neither living things nor even computers themselves are split into a purely ‘structural’ level of biology/physicochemical description and any one abstract’ computational level of machine/psychological description. Rather, they are all hierarchically organized as many levels, each level ‘functional’ with respect to those beneath it but ‘structural’ or concrete as it realizes those levels above it. This is relatively of the ‘functional’/’structural’ or ‘software’/’hardware’ distinction to one’s chosen level of organization has repercussions for functionalist solutions to problems in the philosophy of mind, and for current controversies surrounding connectivism and neural modelling.
  (4) Millikan, Van Gulick, Fodor, Dretake and others have argued powerfully that teleology must enter into any adequate analysis of the intentionality of ‘aboutness’ of mental states such as beliefs and desires, by reference to the states’.  psychological functions. If teleology is needed to explicate intentionality ands machine functionalism affords no teleology, then machine functionalism is not adequate to explicate intentionality.
 It would have been nice to stick with machine functionalism, for the teleologizing of functionalism comes at a price. Talk of teleology and biological function seems to presuppose that biological function seem and other ‘structural’/’states’ of physical systems really have functions in the theological sense. The latter claim is controversial, to say that least. And if it is not literally true, then mental states cannot be type-identified with teleological states. But fortunately for the teleological functions, there is now a small but vigorous industry whose purpose is to explicate biological teleology in naturalistic terms, typically in term of aetiology.
 Functionalism, and cognitive psychology considered as a complete theory of human thought, inherited some of the same difficulties that earlier beset behaviouralism and identity theory. These remaining obstacles fall into two main categories: Intentionality and Qualia problems.
 Propositional attitudes such as beliefs and desires are directly upon states of affairs which may or may not actually obtain (e.g., that the Liberal candidate will win), and are about individuals who may or may not exist (e.g., King Arthur). Franz Clemens Brentano (1838-1917), the German philosopher and psychologist, proposed in Psychology from an Empirical Standpoint (1874) that is the intentionality or directedness of mental states that marks off the mental from the physical, nonetheless,  in which rehabilitates the medieval concentration upon the ‘directedness’ or ‘intentionality’ of the mental as a functional aspect of thought and consciousness.
 However, this solution does not seem quite adequate. There is fist of all the substantial difficulty of specifying the appropriate condition for convariation in a non-circular fashion. Many suspect that this will fall afoul of ‘Brentano’s Thesis’ of the irreducibility of the intentionality: Spelling out the appropriate condition would involve mentioning other intentional/semantic/conceptual conditions, such as that the agent is paying attention, does not believe that perceptual experience is misleading, wants to notice  what is going on, and so forth. This potential circle is particularly troubling for those concerned with ‘naturalizing’ talk of concepts, i.e., of fitting it into theories
of the rest of nature (biology physics).
 Nonetheless, the concept of intentionality was introduced  into modern philosophy by Brentano, who took what he called ‘intentional inexistence’ to be a feature that distinguished the mental from the physical (1960). In this work, the focus on two puzzles about the structures of intentional states and activities, an area in which the philosophy of mind meets the philosophy of language, logic and ontology. We need to note that the term intentionality should not be confused with the terms intention and intension, as there is an important connection between intentions and intentionality, for semantic systems, like extensional model theory, that are limited to extensions and cannot provide plausible accounts of the language of intentionality.
 Brentano raised the question of how any purely physical entity or state could have the property of being ‘directed on or upon’ or about a non-existent state of affairs or object, which is not the sort of feature that ordinary, purely physical objects can have. Whereas the standard functionalist reply is that propositional altitudes have Brentano’s feature because the internal physical states and concepts that realize them represent actual or possible states of affairs.
 Representations, along with mental states especially beliefs and thought are said to exhibit intentionality in that they refer to or stand for something else. The nature of this special property, however, has seemed puzzling. Not only is intentionality often assumed to be limited to humans an possibly a few other species, but the property itself appears to resist characterizations in physicalist terms. The problem is most obvious in the case of ‘arbitrary’ signs, like words, where it is clear that here is no connection between the physical properties of a word and what it denotes. There is no denying it: The Language of Thought hypothesis has a compelling neatness about it. A thought is depicted as a structured of internal representational elements, combined in a lawful way, and playing a certain functional role in an internal processing economy. Relations between thoughts (e.g., the semantic overlap between the thought and ‘Walter loves wine’ and the thought that ‘Walter loves food) consist representational elements. Novel thoughts and the much vaunted systematicity of thought (the fact that being who can think ‘Walter loves wine’ and ‘Walter loves food’ and ‘Mary loves food; can always think ‘Walter loves food?; nd ‘Mary loves wine’( are accounted for in the same way. Once the representational elements and combinatoric rules are I place, of course, such inter-combinations of potential content will occur. The predictive success of propositional attitudes talk (the ascription of e.g., belief and desires such as ‘Walter believes that the wine is good’) is likewise explained on the hypothesis that the public language words pick out real inner representational complexes which are casually potent and thus capable of bringing about actions. And finally, what distinguishes an intensional action from a mere reflex is, on this ,model the fact that intervening between input and action there is, in the intentional case, an episode of actual tokening of an appropriate symbol string. ‘No intentional causation without explicit representation’, as the rallying cry goes. A pretty package indeed, and all for the price - beware.
 What they represent is determined, in, at least, in part, by their functional roles. The notion of a concept, like the related notion of memory, lies at the heart of some of the most difficult and unresolved issues in philosophy and psychology. The word ‘concept’ itself is applied to a bewildering assortment of phenomena commonly thought to be constituents of thought. These include internal mental representations, images, words, stereotypes, senses, properties, reasoning and discrimination abilities, mathematical functions. Given the lack of anything like a settled theory in this area, it would be a mistake to fasten readily on any one of these phenomena as the unproblematic referent of the term. One does better to survey this geography of the area ans gain some idea of how these phenomena might fit together, leaving aside for the time being, just of them deserve to be called ‘concepts’ as ordinarily understood.
 Historically, a great deal has been asked of concepts. As shareable constituents of the objects of attitudes, they presumably figure in cognitive generalizations and explanations of animals’ capacities and behaviour. They are also presumed to serve as the meaning of linguistic items, underwriting relations of translation, definition, synonymy, antonymy, and semantic implication. Much work in the semantics of natural languages, as taking itself t be addressing conceptual structure.
 Concepts have also been thought to be the proper objects of ‘philosophical analysis’, the activity practised by Socrates and twentieth-century ‘analytic’ philosophers when they ask about the nature of justice, knowledge or piety, and expect to discover answers by means of a priori reflection alone.
 The expectation that one sort of thing could serve all these tasks went hand in hand with what has come to be called the ‘Classical View’ of concepts, according to which they have an ‘analysis’ consisting of conditions that are individually necessary and jointly sufficient for their satisfaction, which are known to any competent user of them. The standard example is the especially simple one of [bachelor], which seems to be identical to [legible unmarried male]. A more interesting, but problematic one has been [knowledge], whose analysis was traditionally thought to be [justified true belie].
 This Classical View seems to offer an illuminating answer to a certain form of metaphysical question: In virtue of what is something the kind of thing it is - e.g., in virtue of what is a bachelor a bachelor? - and it does so in a way that supports counterfactuals, it tells us what would satisfy the concept in situations other than the actual ones (although all actual bachelors might turn out to be bald. Its possible that there might be bald ones, since the analysis does not exclude that.
 However, Wittgenstein (1953) raised a different issue of whether a concept actually need have any Classical analysis at all. Certainly, people are seldom very good at producing adequate definitions to terms that they are, nonetheless, competent to use. Wittgenstein proposed that, rather than classical definitions that isolated what, for example, all games had in common, the different uses of the word ‘game’ involved a set of overlapping and criss-crossing ‘family resemblances’. This speculation was taken seriously by Rosch (1973) and Smith and Medin (1981) as testable psychological hypothesis.
 Meanwhile, there are two difficulties. One is that of saying exactly how a physical item’s representational content is determined: In virtue of what does a neurophysiological state represent precisely that the Liberal candidate will win? An answer to that general question is that Fodor has called a ‘psychosemasntics’, and several attempts have been made.
 The second difficulty is that ordinary propositional attitude contents do not supervene on the states of their subject’s nervous systems, but are under-determined by even the total state of that subject’s head. Putnam’s (1975) Twin Earth and indexical examples show that, surprising as it may seem, two human beings could be molecular-for molecular alike and still differ in their beliefs and desires, depending on various factors in their spatial and historical environments. Thus we can distinguish between ‘narrow’ properties, those that are determined by a subject’s intrinsic physical composition, and ‘wide’ properties, those that are not so determined, and representational contents are wide. Yet functional roles are, ostensibly, narrow, how, can propositional attitudes be type-identified with functional roles?
 Leaving all else for reason to posit in giving an account of what someone believes, does essential reference have to be made to how things are in the environment of the believer? And, if so, exactly what relation does the environment have to the belief? Answering these questions involves taking sides in the externalism/internalism consideration. To a first approximation, the externalist holds that one’s propositional attitude cannot be characterized without reference to the disposition of objects and properties in the world - the environment - in which on is situated.
 The internalist thinks that propositional attitudes (especially belief) must be characterizable without such reference. The reason that this is only a first approximation of the contrast is that there can be different sorts of externalism. Thus, one sort of externalist might insist that you could not have, say, a belief that grass is green unless it could be shown that there was some relation between you, the believer, and grass. Had you never come across the plant which makes up lawns and meadows, belief about grass would not be available to you. This does not mean that you have to be in the presence of grass in order to entertain a belief about it, nor does it even mean that you were in its presence. For example, it might have been the case that, though you have never seen grass, it has been described to you. Or, at the extreme, perhaps grass no longer exists anywhere in the environment, but your ancestors’ contact with it left some sort of genetic trace in you, and that trace is sufficient to give rise to a mental state that could be characterized as about grass.
 Clearly, these forms of externalism entail only the weakest kind of commitment to the existence of things in the environment. However, some externalist hold that propositional attitudes require - something stronger. Thus, it might be said that in order to believe that grass is green, you must have had some direct experience - some causal contact- with it during your lifetime. Or an even stronger version might hold that there are beliefs that require that you be in direct contact with the subject matter of these beliefs in order to so much as have them. Obviously, such a strong form of externalism is implausible in connection with a general belief about grass, for example, that it is green. But when it comes to what are called singular beliefs, matters are not so clear. For example, on seeing something bird-like outside the window of my study, I may say, ‘that bird was a Bluejay’, thereby expressing what I believe. Suppose, however, that I never did see a bird on that occasion - it was only a movement of a leaf which I had mistaken for one. In this case, one sort of externalist would insist that, since nothing in my environment answers to the expression ‘that bird’ that I used, then I simply do not have the belief that, that bird was a Bluejay. And this is true even if I myself am convinced that I have the belief. On this strong extern alist stance, propositional attitudes become opaque to their possessors. We can think we believe and desire various things - that our attitudes have certain contents - though we might well just be wrong.
 In contrast, the internalist would insist that the contents of our attitude can be described in ways that do not require the existence of any particular objects or properties in the environment, and this is so even in the case of singular beliefs. There are several motivating factors involved. First, there is the intuition that we do know the  contents of our own minds. I may be wrong about there being a bird, but how can I be wrong about my believing that there is one? One way the internalist might try to embarrass the externalist into agreeing about our interpretation of the here and now, nonetheless,. How to explain our intuition that we have some sort of first-person pronoun authority with respect to the contents of our thoughts. For, on the strong form of externalism, what we actually think is dependent on the environment, and this is something that is as accessible to others as it is to oneself. The second motivation comes from the demands of action explanation. Suppose that I reach for my binoculars just after insisting that I saw the bird in the tree. The obvious explanation for my action would seem to mention, among other things, my belief that there is such a bird. However, since if the externalist is right, then just do not have any such belief, it is unclear how to explain my reaching for the binoculars. Finally, internalist can seem the obvious way to deal with the otherwise puzzling consequences of versions of the Twin Earth thought experiment. Briefly, suppose this time that I really do see the bird, but suppose that my twin - someone who is a molecular duplicate of me on a duplicate plant called ‘twin earth’ - does not. (We can stipulate that the only difference between earth and twin earth at that very time that there really is a bird in the tree on earth, but there is none on twin earth.) As would generally be agreed, my twin would say ‘that bird is a Bluejay’, while pointing in the direction of the tree. After all, being a molecular duplicate of me, one would expect his behaviour to resemble mine as closely as can be imagined. Moreover, it is difficult to deny that his saying believes it. The fact that my twin and I are molecular-for-molecular the same is often reckoned to imply that my twin and I are psychological, as well as physical duplicates. Yet the strong externalist position would be committed to saying that my twin has no such belief, while I do, and this because of the way things are in our respective environments. Yet, if I were suddenly to be in my twin’s shoes - if I were instantaneously transported to twin earth without any knowledge of the move - there could be no doubt that I would say ‘that bird is a Bluejay’. And what reason could be given for saying that my mental state had changed during the transportation? Why, if my saying something counted as evidence for my belief in the one case does not count in the other.
 Given these factors, the internalist is apt to insist that beliefs and other attitudes must be characterizable ‘from the inside’, so to speak. What I share with my twin is a content, though wee obviously do not share an environment that answers to that content in the same way. In not being answerable to how things are in the environment,  it has been suggested that what I and my twin share is a narrow content. The broad or wide content does take the environment into considerations, and it is therefore true that my twin and I do share broad content in the case imagined. However, what the internalist insists is that only the notion of narrow content is up to the task of explaining the intuitiveness that we have about twin earth cases, explanation of action and first-person pronoun authority. To be sure, there are rejoinders available to the externalist in respect to each of these intuitions, and only of its beginning are that we have been touched.
 Questions about the nature of word meaning have drawn attention across the cognitive science disciplines. Because words are one of the basic units of language, linguistics working to describe the design of human language have naturally been concerned with word meaning. Perhaps less obvious, though, is the importance of word meaning to other disciplines. Philosophers seeking to identify the nature of knowledge and its relation to the world, psychologists trying to understand the mental representations and processes that underlie language use, and computer scientists wanting to develop machines that can talk to people in a natural language have all worked to describe what individual words mean, and, mor generally, what kind of thing a word meaning is.
 The two major questions for theories of meaning - How can the meaning of individual words be described? and What kind of thing in general is a meaning? - are difficult to discuss independently. Although ideas about how to describe individual meanings overlap across different views of the nature of meaning, the relative pros and cons of these ideas depend in part on the larger view in which they are embedded.  Therefore, our viewing organizations of the general nature of meaning, with which ideas about how to describe specific meanings are to accredit the manifesting accommodations addressed under them.
 Many people intuitively think of word meanings as something that they have in their heads. Not surprisingly, since psychologists are interested in how knowledge is represented and used by humans, this view of meaning is consistent with how most psychologists treat word meaning. That is, they consider a word meaning to be a mental representation, part of each individual’s knowledge of the language he or she speaks. In fact, psychologists typically have not distinguished between the meaning of a word and conception: For instance, they treat the meaning of [bachelor] as equivalent to a person’s concept of [bachelorhood]. This approach is also shared by linguists in the cognitive linguistic camp, who view knowledge of language as embedded in social and general conceptual knowledge.
 Given this view of word meanings, the central question becomes: ‘What is the nature of the meaning representation? What kinds of information do word meanings (or, concepts) consist of? An answer adopted by many psychologists in the 1970's, and dating back to Plato’s quest to define concepts like ‘piety, ‘justice’,, and ‘courage’, came into philosophy by way of a linguistics theory, as, perhaps, this answer is that what a person knows when they know or knows the meaning of a word is a set of defining (or necessary and sufficient) feature: That is, features that are true of all things the person would call by the name and that together separate those things from all things called by other names. For instance, defining features for the word [bachelor] might be adult, male, and unmarried. If someone’s representation of the meaning of [bachelor] consists of this set of features, then he or she would consider all and only people with those features to be bachelors. Although this sort of analysis was most often applied to nouns, psychologist George Miller and Philip Walterson Lair, in their 1976 book, applied a similar kind of analysis to a large number of verbs.
 A problem for this possibility, though, is raised by an early analysis by the philosopher Ludwig Wittgenstein in 1953. He argued that for many words, there is no single set of features shared by all and only the thins that the word refers to. His famous example is the word ‘game’. Some games involve boards and movable markers, others involved balls and hoops or bats, still others involve singing: Furthermore, some involve a winner and some do not, as some are purely for fun and others are for monetary reward, and s forth. The psychologists Eleanor Rosch and Carolyn Mervis, drawing on Wittgenstein’s analysis, suggested in 1975 that what people know about many common nouns is a set of features having varying strengths of association to the category named by the word. For instance, most fruits are juicy, but a few (like bananas) are not; many fruits are sweet, but some (like lemons and limes) are not; some fruits have a single large pit, while others have many small seeds. The most common features, like sweet and juicy for fruit, are true of prototypical examples but do not constitute necessary and sufficient conditions for using the word. In support of their suggestion, they found that a sample of college students could not list features shared by all the members of several categories, but the student’s judgements of how typical the objects were as members of a category were strongly correlated with how many of the more common category features each had. Linguistics Linda Coleman and Paul Kay argued in 1981 that verbs such as ‘lie; may work in a similar way. They found that the lies considered most typical by their subject sample involved deliberate falsehoods with the intent to deceive, but some acts the subjects verified as lies lacked one or more of these features.
 This prototype view, although capturing more of the apparent complexity associated with many common words, share with the defining features view an assumption that the meaning of a word is a relatively constant thing, unvarying from situation to situation. Yet it has long been noted that the same word can have more than one meaning. For instance, ‘foot’ can refer to a human body part, and end of a bd, or the base of a mountain , which are uses distinct enough to warrant thinking of them as involving different, albeit related, meanings. Further, it is clear that the content in which a word occurs may help to determine how it is interpreted. In the 1980's, Herbert Clark argued that context does more than just select among a fixed set of senses for a word: It contributes to the meaning of a word on as particular occasion of use in a deeper way.
 Specifically, Clark argued that many words can take on an infinite number of different senses. For instance, most people have the knowledge associated with the word ‘porch’ that it refers to a structure used for enjoying fresh air without being completely outdoors. But in the context of the sentence ‘Joey porched the newspaper’., a new meaning is constructed: Namely, ‘threw onto the porch’. And in ‘After the main living area was complete, the builders porched the house’, the meaning ‘built the porch onto’ is constructed. Because there is no limit to the number of context that can be generated for a word, there can be no predetermined list of meanings for a word. Other authors have made related points for less unusual cases of context, arguing, for instance, that the meaning of the word ‘line’ is subtly different in each of many different context (e.g., ‘standing in line’, ‘crossing the line’, ‘typing a line of text’), and that the variations are constructed at the time of hearing/reading the word from some core meaning of the word in combination with the context in which it occurs.
 Although this last view differs from the defining features and prototype views in that it does not treat word meanings as things that are stored in their entirety in someone’s head, all three approaches share the basic assumption that some critical knowledge of meaning is held by individuals. Several issues arise from this assumption. One is how people understand each other, since meaning must somehow be shared among people in order for communication to take place. The defining features view can easily account for how meanings are shared by assuming that everyone will have the same set of defining features for a word. The prototype approach, in proposing that meaning is a much broader set of features with varying strengths of association to the word, opens the possibility that individuals will differ from one another in the features that they represent and the strength of the associations to the word. Each person’s experience with bachelors will be slightly different. One person may think of them as driving fast cars and partying, another may think of them as more like the Canadian bachelor-farmer in the provinces of Manitoba, Saskatchewan and Alberta. Similarly, this version of meaning opens the possibilities that each person’s meaning will change over time as they experience the chance to change. The third view of meaning, by taking meaning to be context-dependent, like-wise implies that a word meaning may differ from person to person and, notably, from situation to situation. And if meaning is person - and situation-dependent, then it is difficult to know if anything should be called the meaning of a word and what the mental representation of a word consists of. The idea that there is some core part of meaning that is invariant across all contexts or instances of a category offers a useful solution to this problem in principle, but in practice, cores for many words may be difficult or impossible to identify, just as were defining features, while having intuitive appeal, at the same time raises a number of difficult issues which must be resolved.
 Most linguistics and many philosophers view word meanings not as something inside individual people’s heads, but as part of a language in a more abstract sense. Many computer scientists likewise seem to take this view of meaning, though they are typically less explicit about such assumptions. Meanings, on this view, are treated as attached to words regardless of the individuals who use them or what they know about them. The most extreme way of formulating this position is to consider meanings to be part of a system that can be characterized in items of its properties without reference to language-users at all, just as the properties of the solar system might be described without reference to its relation to humans (a view expressed, for instance, in the title of linguist Jerrold Katz’s 1981 book, Language and other Abstract Objects). A more moderate formulation is to think of meanings as things fixed by convection within a language community. A word can then be characterized as having some particular meaning within the linguistic community even if so, or even many, members of the community do not know that meaning or have incomplete knowledge of that meaning. For example, the word ‘turbid’ might be characterized as meaning muddy, cloudy, or dense in English, even if not all people who speak English know its meaning.
 In the 1960's and 1970's substantial effort was made by linguistics (and also anthropologists) to describe meanings in terms of features that define the conditions under which something would be labelled by the word. This effort, by investigators such as Jerrold Katz, Jerry Fodor, and others, is in fact the source of the example of defining ‘bachelor as male, adult, and unmarried used by psychologists (adapted there to a more psychological perspective). Although primarily applied to nouns, this sort of defining features analysis was also applied to verbs by a number of linguistics such as James McCawley and Ray
 A major benefit of this approach is its usefulness in attempting to specify how words are related to other words. Within linguistics, doing so has often been taken to be a major goal for a theory of meaning. Thus, linguistics have wanted to capture meanings in a way that would allow them to identify what words are synonymous with other words, what words are antonyms (opposites), what words name things with part-whole relations (as, for example, arm and body), what ones name things with inclusion relations (as, for example, dog and animal), and so forth. Characterizing meanings in terms of defining feature provides a way of doing this: Two words are synonymous if they have the same defining features: Two words have an inclusion relations if the defining features of one are includes in the defining features of the other, and so forth. The defining features approach has also provided a convenient way of representing meaning s and their relation to each other for use in computer programs that attempt to deal with natural language input, and featural approaches along these lines have been widely used within artificial intelligence.
 Another benefit of this approach is that we can then treat some of the individual differences in knowledge about word meanings by saying that a person might not fully grasp whatever the meaning of the word actually is. So, someone who does not understand ‘bachelor’ to mean adult, male, unmarried but only adult and unmarried, do not fully grasp the meaning of ‘bachelor’. To the extent that successful communication and consistency in individual representation of meaning occur, they are presumably achieved because people aim to acquire the meaning given to the word by linguistic convention.
 Nevertheless, several potential serious problems arise for the defining features versions of meanings as public entities. A major one is that, it seems impossible to provide an analysis of many words (such as ‘game’) in terms of defining features. Another ids that, also along the same lines, we might want to include other factures such as ‘likes to party’ and ‘drives a sporty car’ as part of the meaning of ‘bachelor’. One solution to these problems is to expand the notion of meaning to encompass a boarder range of features, as proposed and have been incorporated in some artificial intelligence system for representing meaning. However, these solutions create the problem of trying to decide where word meanings end and general knowledge begins: That also undermine the attempt to provide an account of relations like synonymy and antonymy between words. Another solution, adopted in the 1980's by the linguistic George Lakoff and others, is to view a word having a set of distinct but specifiable meanings that may have a variety of relations, including metaphorical relations like synonymy can be specified and it requires enumerating a potentially very large number of meanings for each word.
 Once, again, is that the meaning of ‘bachelor’ resides in individual heads or belongs to a language like ‘adult’ and ‘male’, however, scholars of meaning since the philosopher Gottlob Frége in the late 1800's have distinguished between two components or aspects of meaning. One, the ‘sense’ or ‘intension’ of a word, is the conceptual aspect of meaning that we have understood so far. The others is the ‘reference’ or ‘extension’ of a word, the set of things in the world that the word refers to. For the word ‘bachelor’, for instance, the reference of the word ids the set of all (real or possible) ‘bachelors’ in the world. In other words the reference aspect of meaning is a relations between a word and the world.
 Psychologists, linguistics, and computer scientists holding any of the views of meaning, insofar as generally to consider the sense of a word to be the primary concern for a theory of meaning, although they would also agree that the theory should account for what entities the word is used to refer to. A view of meaning quite distinct from this perspective, though, has recently been influential, and that is a view that says, essentially, that the meaning of a word is its relation to things in the world: That is, meaning is reference.
 An important argument for this view, derived primarily from analysis of meaning by philosopher Hilary Putnam and Saul Kripke, is based on the observation that the features that one thinks of as constituting the meaning of word could turn out not to be true. For example, a person )or, a language) might specify features like ‘sour’ and ‘yellow’ as meaning of the word ‘lemon’, but it could turn out that these features do not accurately reflect the truth about lemons. Research could reveal that pollution makes lemons yellow and sour, but normally they would be green and sweet. The word lemon would still refer to the set of things in the world that it did before everyone revised their knowledge of the properties of lemons. Similarly, new scientific discoveries could add to or alter beliefs about the properties on many objects, but those changes in the properties associated with the words would not change the set of things correctly namely by the word. Putnam suggested, on the basis of these and other arguments, that words function simply to pick out sets of things in the world. On this referential view, the properties constitute a stereotype of what the object is like (or seems to be like), nut they do not constitute the meaning of the word. As Putnam wrote in advocating thus view in 1973: ‘Cut the pie any way you like’, meanings’ ‘just are not in the head’. (And therefore, according to this view, they ‘just ain ‘t’ definitions held by linguistic community).
 A benefit of this referential view of meaning is that it provides an account of stability in meaning and communication: A word refers to the same set of things in the world regardless of variation in knowledge among people, and use of a word to refer to a particular set of things can be passed from generation to generation regardless of changes in belief about properties of the object. However, it also has weaknesses and one prominent one is that the analysis des not seem to apply to many common words. Or example, the word ‘bachelor’ seems intrinsically to involve the property of being unmarried. Although we can imagine researchers discovering that lemons really are green, it is not possible for researchers to discover that bachelors really are married people. Even if all men previously thought to be unmarried turned out to be married, we would not change the properties associated with bachelor, we would say that these men were not bachelors after all. Likewise, ‘island’ seems to intrinsically refer to a certain kind of motion, and any activity not involving that motion just wouldn’t be running. In such cases, having the associated properties does seem to be critical to whether or not the word can be applied to the object. If the referential view is correct for some words, this observation raises the interesting possibilities that the nature of the meanings may differ for different words, and one analysis of meaning may not be appropriated for all words.
 Placing all else aside, are nonetheless, that the Logical positivists have in themselves attributed many of the confusions and uncertainties of science, particularly those found in the social and behavioural sciences, to unclarity in the language. Even more strongly, they claim that the quandaries that beset other areas of human inquiry, including politics, religion and areas of philosophy like metaphysics, resulted from unclear use of language. When language is not governed by strict rules of meaning , the utterly meaningless statements. In calling a statement meaningless, the positivists were not merely asserting that the statement was false but something worse - the statement was not really understandable. The kind of statement the positivists had in mind is a statement like, ‘God is love’. Consequently, they viewed theological debates, for example, not as substantive debates for which there were objective answers, but simply as confused discourse. The remedy for such confusion was to attend carefully to the principles governing meaningful discourse and to restrict oneself to those domains where language could be used meaningfully. The positivists did admit that language could serve other functions than making true or false statements. For example, they thought that literature and poetry could be used to arouse emotional responses or inspire action. But science, they maintained, was concerned was with truth and therefore had to restrict itself to discourse for which clear principles of meaningfulness was available.
 In their discussions of meaning the positivists followed the classical ‘empiricists’ in linking knowledge to experience, but they advocated one important change. The classical empiricists treated ideas as the units of thinking and viewed these ideas as causal products of sensory experience. The logical positivists rejected ideas as fuzzy entities. Rather, they took linguistic entities - sentences and words - to be the basic vehicles of meaning. They proposed the criterion of verification to explain how these linguistic entities could be appropriately related to experience. According to this criterion, the meaning of a sentence was the set of conditions that would show that the sentence was true. Although these conditions would not actually occur if the sentence was false, we could still state what would be the case if it was true. Because only sentences and not individual words could be true or false, the meaning of words had to be analysed in terms of their roles in sentences. This account of meaning became known as the ‘verifiability theory of meaning’.
 Some instances, the logical positivists maintained, could be directly verified through experience. Sensory exposure could tell us directly that these sentences were true or false. The positivists referred to these sentences variously as ‘protocol sentences’ or ‘observation sentences’. There was considerable disagreement amongst positivists as to which sentences counted as such. Some, like the early politists Rudolf Carnap (1891-1970), whereby was probably more influential than any other thinker in combining a basic empiricism with the logic tool s provided by Frége and Russell, and it is in his works that the m ain achievements (and difficulties) of logical positivism are best exhibited. Carnap’s first major work was, ‘Der logische Aufbau der welt’ (1928, trs. As The Logical Structure of the World, 1967). However, a launching gasification for which the celebration in ‘logische der Sprache (1934, trs, as The Logical Syntax of Language, 1937). Refinements to his syntactic and semantic views continued with Meaning and Language, 1947, while a general loosening of the original idea of reduction culminated in the great ‘Logical Foundations of Probability’, the most important single work of ‘confirmation theory’, in 195. Other works concern the structure of physics and the concept of entropy.
 Just the same, Carnap (1928/1967), restricted observation sentences to those characterized our phenomenal experience (e.g., ‘I am sensing a blue colour patch now’) Others like the Austrian philosopher and social theorist Otto Neurath (1932), maintained that sentences about observable parts of the world (e.g., ‘the sun is shining’) could be directly verified. For the most part, positivists took observation sentences to refer to physical states of the world, producing a biassed predetermine which is physically observable.
 Other sentences in a language could not be verified directly through experience. This particularly true of sentences that contain theoretical terms (e.g., force) that do not directly refer to observable features or objects. To explicate the meaning of these terms the positivists focussed on ways in which the truth or falsity of sentences using these terms could be determined indirectly via other sentences that were observational. At this point, logical analysis became important, for the positivists had to explain the logical relationship between two sentences whereby one could serve to explicate the meaning of the other. Initially, a number of positivists proposed to ‘translate’ all sentences referring to theoretical entities into observable sentences. Because they limited themselves to the tools of symbol logic, the kind of translation with which the positivists were concerned was not aimed at preserving the connotation of the theoretical sentences, but an identifying sentence that were true under the same empirical conditions. Thus, translations consist of biconditional sentences that assert that one statement (the theoretical statement) is true if only if another, possibly complex statement (the observational statement) is true. These statements have a unusual characteristic. Because they only articulate the meaning of one sentence in terms of another sentence, they do not depend on experience in any way and so cannot be refuted by experience. Such statements are often referred to as ‘analytic statements’ to distinguish them from ordinary sentences whose truth depends on or upon how the world is.
 This attempt to explicate the meaning of all scientific discourse in terms of observational conditions is closely related to the very influential doctrine associated with the American physicist and mathematician Percy Bridgman (1927), of operational definitions. According to this doctrine, in introducing a theoretical concept, it is necessary to specify through which one can confirm or disconfirm statements using that term. Bridgman’s notion of an operational definition extends the positivists conception of an observation term by supplying procedures for producing the requisite observation.
 One of the issues in cognitive science to which the verifiability theory of meaning has been applied is the question of wether machines can think. In order to render this into a meaningful question, the positivists require that it be translated into a sentence that can be confirmed or disconfirmed observationally. Turing’s (1950) famous test for machine thinking provides the kind of thinking that would require. Turing proposed that we should accept a machine as thinking when we could not distinguish its behaviour (e.g., in answering questions and carrying on a dialogue) from that of a thinking human being. Of course, we also confront problems in deciding whether another being in thinking, or is simply automation. The verificationist theory of meaning, however, advocates the same treatment of this case - explicate what thinking is in terms of this kind of behaviour a thinking being would perform. This treatment construes the concept of thought as referring not to some unobservable activity but as something detectable in the behaviour of organisms or computers.
 The criterion that theoretical terms have to be translatable into observational terms was quickly recognized to be too strong. First of all, it is common for theoretical terms to be linked with experience in more than one way. This is particularly true for measurement terms for which there may be several different observational criteria. Generally, scientists will not accept just one of these as the definition, but view them as giving alterative criteria. Some of these may be discounted if several of the others all support a common measurement. This practice cannot be understood if one insists that there be a single definition translating theoretical terms into, dispositional term ‘soluble’, may not be translatable into observational terms. An object’s property of being soluble cannot be correlated directly with observable features of the object except when the object is placed in water. Many soluble objects will never be placed in water. Even worse, the dispositional term cannot be translated into a conditional sentence (e.g., if it is placed in water, then it will dissolve). The reason is that in symbolic logic a sentence of the form ‘if, . . . then . . . is defined as true if the antecedent is false. This would make any object that was never placed in water soluble.
 To account for the meaning of such terms, which contemporary science seems clearly to require, positivists attempted to weaken their verifiability conditions. Carnap proposed that a dispositional term like ‘soluble’ could be translated by the following sentence (which he termed, ‘reduction sentence):
‘If x is placed in water, then x will dissolve if and only if x is soluble’.
Such a reduction sentence overcomes the previous objection because it does not imply that something never placed in water is soluble. It also has the consequence that under conditions where the test conditions are never investigated (e.g., where the object is destroyed before it can be placed in water) as we will be able to determine the truth of the theoretical sentence. Unfortunately, this means that the initial aspirations of the verifiability criterion are not achieved because there will be reduction sentences for ter`ms even though we may be powerless to verify and actualize applicability of the term in specific instances. But at least, according to the positivists, we know what conditions we claim hold when we make a statement using the term.
 In cognitive anthropology, at least, the limitation of the cognitive perspective has been recognized, mainly with reference to the problem of motivation. If people have a lot of scripts and schemata in their heads, what makes them emotionally compelling are an extremely salient and important aspect of human mental life. However, until recently they have not attracted much attention in cognitive science. Despite this neglect by cognitive theoretical perspectives that cognitive scientists will have to address as they bring emotions into their purview: (Is it the physiological sort in the cognitive aspects of an emotional experience that primarily determine which emotion is being experienced? (2) Are emotions culturally specific or widely shared across cultures? (3) Are either emotions themselves or the causes that elicit them innate in one or more of that word’s several senses? These issues of emotional indifferencing do vary within the different theoretical perspectives that are a direct combination that each suggests that emotions must be investigated by looking at detailed exemplifications that emotional context of thought and resultant behaviours, are, that, emotion is not an individualistic property.
 These complications do not suffice to explain philosophy’s neglect to the emotions. Philosophers, after all, tend rather to be fond of complications. Even so, this neglect is both relatively recent and already out of fashion. Most of the great classical philosophers - Plato, Aristotle, Spinoza, Descartes, Hobbes, Hume - has had recognizable theories of emotion. Yet in twentieth-century Anglo-American philosophy and psychology, the increasing attention of most recently devoted criteria to emotion has had an air of innovation. Under the influence of a ‘tough-minded’ ideology committed to behaviouralism, theories of action or the will, and theories belief or knowledge, had seemed more readily achievable than theories of emotion. Again, recently dominant Bayesian-derived economic models of rational decision and agency are essentially assimilative models - two-factor theories, which view emotion either as a species of belief, or as a species in expressing desire.
 That enviably resilient Bayesian model been cracked, in the eyes of many philosophers, by such refractory phenomena as the ‘weakness of will’. As such, the weakness of will, as is the case of a traditional descriptive rationality seems to be violated, insofar as the ‘strongest’ desire does not win, even when paired with the appropriate belief, whereby each in the belief indicates a state of some kind of arousal a state that can prompt some activities and interfere with others. These states are associated with characteristic feelings, and they have characteristic bodily expressions. Unlike moods they have objects: One grieves over some particular thing or is angry at something. Different philosophical theories have tended to highlight one or other of these aspects of emotion. Pure arousal theory imagines a visceral reaction triggered by some event, which stands ready to be converted into one emotion or another by contextual factors. Theories based on the feel or ‘qualia’ of an emotion were put forward by writers such as Hume and Kant, nut the approach meets difficulty when we consider that an emotion is not a raw feel, but is identified by its motivational powers, and their function is prompting action. The characteristic expression of emotion was studied extensively by Darwin, resulting in the classic, The Expression of the Emotion in Man and Animals’, (1872). In 1884, James published what became known as the James-Lange theory of emotion whose main contention is that we feel as we do in virtue of the bodily expressions and behaviour that we are prompted towards, than the other way round, ‘our feelings of the changes as they occur as ‘our emotion’. Again, it is not clear how such a theory would accommodate the directed, cognitive side of emotions that have a specific objects, than being simply the experience of bodily change. Directly opposing this some philosophers have the emotions, derived from Stoicism, seeing them simply as judgement fear of the dog is no more than the judgement that it is dangerous or a threat to one’s well-being. The Stoics thought that as judgements the emotions were typically false, but modern cognitive theories tend to be more generous to them, often emotions are often an admirable moral adaptation. Other questions concern the cultural variability of emotion, and the dependence of some emotion, but not all, on the existence of linguistically adequate modes of expression and self-interpretation.
 What is distinctive about emotions is perhaps precisely what made them a theoretical embarrassment: That they have a number of apparently contradictory properties. In what follows, are five areas in which emotion’s pose specific philosophical puzzles: Emotion’s relation to cognition; emotions and self-knowledge; the relation of emotions to their objects; the nature of emotional intensity and the relation of emotions to rationality.
 It is a common-place (whether true or false) that emotions are in some sense ‘subjective’. Some have taken this to mean that they reflect nothing but the peculiar consciousness of the subject. But that conclusion follows only if one adopts a fallacious equation of point of view and subjectivity. The existence of ‘perspectivity’ does not invalidate cognition, in that emotional states are perspectival, therefore, need not bar them from being cognitive or playing a role on cognition. There are at least three ways in which emotions have been thought to relate to cognition:
  (1) As stimulants of cognition: Philosophers have been interested in learning from psycho-physiologists that you would not learn anything unless the limbic system - in part of the brain most actively implicated in emotional states - is stimulated at the time of learning.
  (2) Many emotions are specified in terms of propositions: One cannot be angry with someone unless one believes that person guilty of some offence, one cannot be jealous unless one believes that one’s emotional property is being poached on by another. From this, it has ben inferred that emotions are (always? Sometimes?) cognitive in the sense that they involve ‘propositional attitudes’. This claim is relatively weak, however, since the existence of a propositional attitude is at best a necessary, but not a sufficient condition of the existence of an emotion.
  (3) The most literal interpretation of cognitivism about emotions would be committed to ascribing to emotions a ‘mind-to-world direction of fit’. The expression ‘direction of fit’, which is due to Searle (1983), distinguishes between an essentially cognitive orientation of the mind, in which success is defined in terms of whether the mind fits the world (a mind-to-world direction of fit) and an essentially conative orientation. In which success is defined in terms of the opposite, world-to-mind, direction of fit. We will what does not yet exist, and deem ourselves successful if the world is brought into line with the mind’s plan.
A view ascribing to emotions a true mind-to-world direction of fit would involve a criterion of success that depended on correctness with respect to some objective property. Such a view was first defended by Scheler (1954), and has in general had more currency as a variant of an objectivists theory of aesthetics than as a theory of emotions as a whole.
 To take seriously cognitivism in this sense, is to give a particular answer to the question posed long ago in Plato’s, Euthyphro: Do we love ‘X’- mutatis mutandis for the other emotions - because ‘X’ is loveable, or do we declare ‘X’ to be lovable merely because we love it? One way to defend a modest objectivism, in the sense of the first alternative, is to explore certain analogies between emotion and perception. It requires first that we define clearly what is to count as ‘objectivity’ in the relevant sense. Second, it requires that we show that there is a valid analogy between some of the ways in which we can speak of perception as aspiring to objectivity and ways in which we can say the same of emotion.
 Emotions are sometimes said to be subjective in this sense: That they merely reflect something that belongs exclusively and contingently to the mind of the subject of experience, and therefore do not covary with any property that could be independently identified. This charge presupposes a sense of ‘objective’ that contrasts with ‘projective’, in something like the psychoanalytic sense. The way that psychoanalytic explanation is understood has immediate implications for one’s view of its truth or acceptability, and thus is of course a notoriously a controversial matter. However, Freud clearly regarded psychoanalysis as engaging principally in the task of explanation, and held fast to claims for its truth in the course of alterations in his view of the efficacy of psychoanalytic treatment.
 In terms of the analogy of perception, to say that emotions are universally subjective in this sense would be to claim that they resemble hallucinations more than veridical perception. The perceptual system is capable of the sort of vacuous functioning that leads to perceptual mistakes. Similarly, emotions may mislead us into ‘hasty’ or ‘emotional’ judgements. Nonetheless, the lack of perceptual capacities can be a crippling handicap in one’s attempt to negotiate the world: In a like manner, a lack of adequate emotional response can hinder our attempts to view the world correctly and act correctly in it. This explains why we are so often tempted to take seriously ascription of reasonableness or unreasonableness, fittingness or inappropriateness, for common emotions. The big drawback of this view is that it is quite unclear how independently to identify the alleged objective property.
 Closely related to the question of the cognitive aspect of emotion is the question of its passivity. Passivity has an ambiguous relation to subjectivity. In one vein, impressed by the bad reputation of the ‘passions’ as taking over our consciousness against our will, philosophers have been tempted to take the passivity of emotions as evidence of their subjectivity. In an another vein, however, represented especially in the last few years by Robert Gordon (1987), philosophers have noted that the passivity of emotions is sometimes precisely analogous to the passivity of perception. How the world is, is not in our power. So it is only to be expected that our emotions, if they actually represent something genuinely and objectively in the world, should not be in our power either. To this extent, the cognitive model holds out rather well, while at the same time suggesting that our common notion of what cognition amounts to may be excessively narrows.
 We often make the ‘Cartesian’ assumption that if anyone can know our emotions it is ourselves. Descartes said it thus: ‘It is impossible for the soul to feel a passion without that passion being truly as one feels it’. The existence of first person authority is not an empirical discovery, but rather a criterion, among others, of what a mental state is. Among others, so it can happen that we concede error on occasion. But exceptions do not throw in doubt the presumption that we know our own minds. What accounts for this presumption? Introspection offers no solution, since it fails to explain why one’s perceptions of one’s own mental states should be any more reliable than one’s perceptions of anything else. Even so, that ‘those that are most agitated by their passions are not those who know them best’. In fact, emotions are one of our avenues to self-knowledge, since few kinds of self-knowledge could matter more than knowing one’s own repertoire of emotional responses. At the same time, emotion are both the cause and the subject of many failures of self-knowledge. Their complexity entails several sources for their potential to mislead or be misled. Insofar as most emotions involve belief, they inherit the susceptibility of a latter self-deception. Recent literature on self-deception has dissolved the air of paradox to which this once gave rise. But there are also three distinct problems that are specific to emotions.
 The first arises from the connection of emotion with bodily changes. There is something right in William James’s notorious claim that the emotion follows on, than causing the voluntary and involuntary bodily changes which express it. Because some of these changes are either directly or indirectly subject to our choices, we are able to pretend or dissimulate emotion. That implies that we can sometimes be caught in our own pretence. Sometimes we identity our emotions by what we feel, and if what we feel has been distorted by a project of deception, then we will misidentify our own emotions.
 A second source of self-deception arises from the role of emotions in determining salience among potential objects of attention or concern. Poets have always known that the main effect of love is to redirect attention, when in love. Nonetheless, one is not always able to predict, and therefore to control, the effects that redirect attention might produce, the best explanation for this familiar observations require us to take seriously the hypothesis of the unconscious: If among the associations that are evoked by a given scene are some that I can react to without being aware of what they are, then I will not always be able to predict my own reactions, even if I have mastered the not altogether trivial task of attending to whatever I choose. Where the unconscious is, self-deception necessarily threatens.
 This brings us to the third source of emotional self-deception: The involvement of social norms in the determination of our emotions. This possibility arises in two stages from the admission that there are unconscious motivations for emotions. First, if I am experiencing an emotion that seems altogether inappropriate to its occasion, I will naturally confabulate an explanation for it. A neurotic who is unreasonably angry with his wife because he unconsciously identifies her with, his mother will not rest content with having no reason for his anger. Instead, he will make one up. Moreover, the reason he makes up will typically be one that is socially approved.
 When we are self-deceived in our emotional response, or when some emotional state induces self-deception, there are various aspects of the situation about which self-deception can take place. These relate to different kinds of intentional objects of emotion.
 What does a mood, such as free-floating depression or euphoria have in common with a precisely articulable indignation? The first seems to have as its object nothing and everything, and often admits of no particular justification: The second has a long story to tell typically involving other people and what they have done or said. Not only  those people but the relevant facts about the situation involved, as well as some of the special facts about those situations, aspects of those facts, the causal role played by these aspects, and even the typical aims of the actions motivated by the emotions, can all in some context or other be labelled objects of emotion. Objects are what we emote at, with, to, because of, in virtue of or that the directness or ‘aboutness’ of many, if not all conscious states. The term - intentionality - was used by the scholastics but revived in the 19th century by Brentano,. Our beliefs, thoughts, wishes, dreams, and desires are about things. Equally the words we use to express these beliefs and other mental states are about things. The problem of intentionality is that of understanding the relation obtaining between a mental state, or its expression, and the things it is about. First, if I am in some relation to a chair, for instance by sitting on it, then both it and I must exist. But while mostly one thinks about things that exist, sometimes (although this way of putting it has its problems) one has beliefs, hopes and fears about things that do not, as when the child expects Santa Claus and the adult fears the axeman. Secondly, if I sit on the chair, and the chair is the oldest antique in Toronto, then I sit on the oldest antique in Toronto. But if I plan to avoid the mad axeman, and the mad axeman is in fact my friendly postman. I do not therefore plan to avoid my friendly postman.
 Intentional relations seem to depend on how the object is specified, or as Frége put it, on the mode of presentation of the object. This makes them quite unlike the relations whose logic we can understand by means of the predicate calculus, and this peculiarity has led some philosophers, notably Quine, to declare them unfit for use in serious science. More widespread is the view that since the concept is indispensable to deal with the central feature of the mind, or explain how science may include intentionality. One approach is to suggest that while the linguistic forms in which we communicate fears and beliefs have a two-faced aspect, involving both the objects referred to, and the mode of presentation under which they are thought of, wee can see the mind as essentially directed onto existent things, and extensionally related to them. Intentionality then becomes a feature of language, rather than a metaphysical or ontological peculiarity of the mental world.
 It seems to be an irreducible differentia of emotions that they can be measured along a dimension of intensity. This corresponds neither in the strength of desire nor to a belief’s degree of confidence. What does mild distaste have in common with the most murderous rage? Is it just a matter of degree? Or does intensity necessarily bring with it differences in kind? Two different sorts of considerations favour endorsing the latter view. The difference between them illustrates a characteristic methodological dilemma faced by emotions research. The first approaches taxonomy through social significance: Mild distaste is one thing, rage quite another, in the sense that the circumstances in which the first or the second is generally appropriate and acceptable are radically disjoint. From this point of view, then, they must obviously be classed as entirely different phenomena. But a similar response might be derived from an entirely different approach: One might look at the brain’s involvement in the two cases and find (perhaps) the first to be an essentially cortical response, while the second involves activity of the limbic system or even the brain stem -what has been dubbed as the ‘mammalian’ or ‘crocodile’ brain. In this case the classification of the two as entirely separate phenomena might have a strictly physiological basis. How are the two related?
 The very notion of intensity is problematic exactly to the extent that the emotions call for disparate principles of explanation. Might a physiological criterion settle the question? One could stipulate that the most intense emotion is the one that involves the greatest quantity of physiological ‘disturbance’. But this approach must implicitly posit a state of ‘normal’ quietude hard to pin down among the myriad different measures of physiological activity one might devise. To select a measure that will count as relevant, one will inevitably have to resort to another level of more functional physiological activity that are relevant to the social functions subserved by those emotions? And what are the mental functions that should be deemed most important in the context of the relevant demands of social life? At that point, while physiological explanations may be of great interest, there is no hope from their quarter of any interesting criteria for emotional intensity.
 There is a common prejudice that ‘feelings’ a word now sometimes vulgarly used interchangeably with ‘emotions’, nether owe nor can give ant rational account of themselves. Yet we equally commonly blame others or ourselves for feeling ‘not wisely, but too well’, or for targeting inappropriate objects. Yet we have sen, the norms appropriate to both these types of judgement are inseparable from social norms, whether or not these are endorsed. Ultimately they are inseparable from conceptions of normality and human nature. Judgements of reasonableness therefore tend to be endorsed or rejected in accordance with one’s ideological commitments to this or that conception of human nature. It follows that whether these judgements can be viewed as objective or not will depend on whether there are objective facts to be sought about human nature. on this question, we fortunately do need to pronounce. It is enough to note that there is no logical reason why judgements of reasonableness or irrationality in relation to emotions need any other judgements of rationality in human affairs.
 In contrast with this thoroughgoing rationalism, Kant’s critical philosophy may be seen as attempting a more restrictively affirmative account. On this view reason supplies the human mind with regulative ideals, not constitutive ideas. Such principles
guide us in the systematization of knowledge but generate irresoluble antinomies if interpreted as representations of features of reality. Inn ethics, too, on Kant’s view, reason guides our choice of maxims on which to act, but does not actually supply those maxims itself.
 However, negative theorizing about rationality generates a sceptical challenge to one or more culturally accepted principles. Even the fundamental laws of deductive logic have been exposed to such challenges. For example, the principle that every proposition is either true or false but bot both was called into question in the Fourth century Bc. by the paradox of Eubulides (Suppose only one sentence is written on a piece of paper, viz. ‘The sentence on this piece of paper is false’: then that sentence is arguably both false if it is true and true if it is false.)
 But in modern philosophy the most influential sceptical challenge to everyday beliefs about rationality was originated by Hume. Therein, he argued the impossibility of reasoning from the past to the future or from knowledge about some instance of a particular kind of situation to knowledge about all instances of that kind. There would be nothing contractory, he claimed, in supposing both that the sun has always  risen in the past and that it would not rise tomorrow. In effect, therefore, Hume assumed that only valid standards of cognitive rationality were those of the first three kinds listed  - deductive, mathematical or semantical. Induction was not a rational procedure, on his view, because a rational procedure, so to exercise reason in one or another of these three roles were shown on the grounds that induction should be held to be a valid process in its own right and with its own criteria of good and bad reasoning.
 Nevertheless, there is a further contribution that the study of emotions can make to our understanding of rationality. The clearest notions associated with rationality are coherence and consistency in the sphere of beliefs, and maximizing expected utility in the sphere of action. But these notions are purely critical ones. By themselves, they would be quite incapable of guiding an organism towards any particular course of action. For the number of goals that it is logically possible to posit at any particular time is virtually infinite, and the number of possible strategies that might be employed in pursuit of them os orders of magnitude larger. Moreover, in considering possible strategies, the number of consequences of any-one strategy is again infinite, so that unless some drastic preselection can be affected among the alternative their evaluation could never be completed. This gives rise to what is known among cognitive scientists as the ‘Frame Problem’: In deciding among any range of possible actions, most of the consequences of each mus t be eliminated from consideration a priori, i.e., without any time being wasted on their consideration. That this is not as much of a problem for people as it is for machines may well be due to our capacity for emotions. Emotions frame our defining parameters as taken into account in any particular deliberation. Second, in the process of rational deliberation itself, they render salient only a tiny proportion of the available alternatives and of the conceivably relevant facts. In these ways, then, emotions would be all-important to rationality even if they could themselves be deemed rational or irrational. For they winnow down to manageable size the number of considerations relevant to rational deliberation, and provide the indispensable frame-work without which the question of rationality could never be raised.
 `As a matter-of-course, the theory of knowledge as distinguished from two or more others inferred on or upon its central questions include, the origin of knowledge, the place of experience in generating knowledge, and the place of reason in doing so. The relationship between knowledge and certainty, and between knowledge and the impossibility of error, the possibility of universal ‘scepticism’ and the changing forms of knowledge that arise from new conceptualizations of the world. All of these issues link with other central concerns of philosophy, such as the nature of truth and the nature of experience and meaning. It is possible to see epistemology as dominated by two rival metaphors. One is that of a building or pyramid, built on foundations. In this conception it is the job of the philosopher to describe especially secure foundations, and to identify secure modes of construction, so that the resulting edifice can be shown to be sound.
 This metaphor favours some idea of the ‘given’ basis of knowledge, and of a rationally defensible theory of confirmation and inference as a method of constitution. The view in epistemology that knowledge must be regarded as a structure raised upon secure, certain foundations. These are found in some combination of experiences and reason, with different schools (‘empiricism’, ‘rationalism’) emphasizing the role of one over the other. The other metaphor is that of a boat or fuselage, that has no foundation but owe its strength to the stability given by its interlocking parts. This rejects the idea of a basis in the given, and favours ideas of ‘coherence’ and ‘holism’, but finds it harder to ward off scepticism.
 The problem of defining knowledge in terms of true belief plus some favoured relation between the believer and the fact began with Plato’s view in the Theaetetus that knowledge is true belief plus a logos.
 The preference for reason over sense experience as a source of knowledge began with the Eleatics, and played a central role in Platonism. Its most significant modern development was in the 17th-century belief that the paradigm of knowledge was the non-sensory intellectual intuition that God would have into he workings o f all things, and the human beings task in their acquaintance with mathematics. The Continental rationalists, notably Descartes, Leibniz and Spinoza are frequently contrasted with the British empiricists Locke, Berkeley and Hume, but each opposition is usually an over-simplicity of more complex picture, for example, it is worth noticing the extent to which Descartes approves of empirical equity, and the extent to which Locke shared the rationalist vision of real knowledge as a kind of intellectual intuition.
 In spite of the certainty of Kant, the subsequent history of philosophy has tended to minimize or even to deny the possibility of ‘deductive knowledge’ so rationalism depending on this category has also declined. However, the idea that the mind comes with pre-formed categories that determine the structure of our language and ways of thought has survived in the works of linguistics influenced by Chomsky. The term rationalism is also more broadly for any anti-clerical anti-authoritarian humanism, but it is unfortunate that it is empiricists such as Hume who are in this other sense rationalists.
 A fully formalized confirmation theory would dictate the degree of confidence that a rational investigator might have in a theory, given some body of evidence. The grandfather of confirmation theory is the German philosopher, mathematician and polymath Wilhelm Gottfried Leibniz (1646-1716), who believed that a logically transparent language of science would be able to resolve all disputes. In the 20th-century as fully formal confirmation theory was a main goal of the ‘logical positivists’, since without if the central concept of verification empirical evidence itself remains distressingly unscientific. The principal developments were due to the German logical positivist Rudolf Carnap (1891-1970), culminating in his ‘Logical Foundations of Probability’ (1950). Carnap’s idea was that the meaning needed would be the proportion of logical possible states of affairs in which the theory and the evidence both hold, compared to the number in which the evidence itself holds.
 All the same, the ‘range theory of probability’ holds that the probability of a proposition relative to some evidence, is a preposition of the range of possibilities under which he proposition is true, compared to the total range of possibilities left open by the evidence. The theory was originally due to the French mathematician Simon Pierre LaPlace (1749-1827), and has guided confirmation theory, for example in the work of Carnap. The difficulty with the theory lies in identifying sets of possibilities so that they admit of measurement, LaPlace appealed to the principle of ‘difference’ supporting that possibilities have an equal probability unless there is reason for distinguishing them. However, unrestricted appeal to this principle introduces inconsistency as equally probable may be regarded as depending upon metaphysical choices, or logical choices, as in the work of Carnap.
In any event it is hard to find an objective source for authority of such a choice, and this is one of the principal difficulties in front of formalizing the theory of confirmation.