Notes from a second year module in the philosophy of mind.
To distinguish the faculties of our mind from the features of our brain (which allows for dualism but doesn't necessarily imply it), we can divide our mind into categories of states and processes. Some are ambiguous in their nature, and may be either a state or a process.
Conscious experiences - from these we form beliefs about experiences that may become knowledge. The opposite would be representational experiences, e.g. the knee's reflex, whereby its reaction is merely a representation of the input; no conscious process takes place
Beliefs, desires, emotions
Thought - language representing a conscious experience
Action - the manifestation of a conscious experience in the body; as opposed to mere behaviour based upon representational experience
Unconscious experiences
Interpersonal relationships develop around representations of mental states; I am aware of you, and I know about your various mental conditions. I do not know what it is like to have your mental states, hence relationships are purely representational.
Mental states and processes are susceptible to judgement; this implies some responsibility for our mental states, though in the case of many, this is dubious (e.g. unconscious processes, emotions, and especially actions based on them).
The mind-body problem is essentially this: how are mental states and processes linked to bodily states and processes?
Can a state of mind merely be a bodily state? I.e. can meat experience? What does studying a person?s brain tell you about their mind, their experiences and emotions?
Can a state of the body merely be a mind state?
Here are two essays I have written on the subject, rather than notes. The first focuses more on the metaphysics of dualism and dual-aspect theory, whilst the second focuses on dualism as a theory of mind.
In his quest for knowledge about which we can be absolutely certain, Descartes developed a theory of the nature of our world called Dualism, which proposes that the world consists of two entirely distinct kinds of substance: extended substance (res extensa) and thinking substance (res cogitans). He suggested that our bodies, including our brains, are made up of extended substance, and that our mind is made up of thinking substance. But this left him a problem which he could not satisfactorily resolve - how do the mind and body interact, if they are fundamentally different in nature? His problem can only be resolved when we reject his substantive dualism, and instead work from the premise that mind and body are different, but not different kinds of substance, such that they can still interact.
Descartes developed his substantive dualism through reasoning, and it can be backed up by experiential evidence. He began with the definition of substance offered by Aristotle: that which depends on no other for its existence, meaning that everything else is merely an attribute of some substance. So grass is a substance, whilst green is not, because green can only exist as an attribute of grass, or some other substance. To Descartes, the most important property of a substance, that distinguishes it from all other things, is that it can (in thought experiments, at least) exist independently of anything else.
In his first meditation, Descartes considered the nature of his existence, and he found he could doubt everything about it except that he was thinking. He even doubted he has a body, because he could conceivably be no more than a brain in a scientist's laboratory, or even an electrical charge being carried by some other substance. So he believed that he could, in thought experiments, conceive of himself as nothing but a mind, without a body. This meant that his thoughts could exist independently of his body, and as our body can, for short periods of time whilst unconscious, still function, it is true to suggest that our body can exist independently of our mind (Meditations).
So Descartes concluded that our mind and our body must be two fundamentally different kinds of substance. This idea may be supported by an examination of music. A scientist could take a short piece of music and explain in great detail the physics of the sound waves and how they produce a vibration in our ear which our brain then interprets as sound. But the scientist couldn't explain what the music "sounds" like; he could never experience the music without playing it. Furthermore, that music might be transmitted through the air in sound waves, written down on paper as shapes in ink, or stored on a computer's hard drive as magnetic signatures; here the nature of the extended substances is quite different, and yet the nature of the music remains the same. In other words, the essential qualities of the music have nothing to do with the vibrating molecules that transmit then, or the paper that stores them. So thinking substance and extended substances are quite distinct in their nature.
So there may be two kinds of substance that are distinct, but they cannot separate; rather they are "closely conjoined" since we can think about "pain and other sensations... quite unexpectedly" (Principles). So if they are not separate, and indeed are closely conjoined, they must in some way interact, but how can this be possible if they are fundamentally different? How can something material be affected by something wholly immaterial? Descartes thought that there was a particular section of the brain through which mind and body interact, but that explanation is far from satisfactory as it still doesn't provide an explanation of how the material and immaterial interact.
In fact, when one considers it, it seems wholly inconceivable that such a thing could occur. No satisfactory material analogy might be used here, but it is as absurd as suggesting that a bachelor might be married, or that one equals two. It is simply a logical impossibility, and so it is on this problem that Descartes' dualism fails. But this does not necessarily mean that we should do away with the idea that mind and body might be in some way different, even distinct. I have only shown that we cannot support Descartes' substantive dualism, meaning that we cannot support the notion that mind and body are fundamentally different kinds of substance. But what if they were simply different aspects of the same substance, and so could be distinct and separable, but not substantially different?
This idea was first entertained by Spinoza in his work entitled Ethics. Spinoza was a strong theist, and was interested both in resolving the problems raised by substantive dualism, and in demonstrating the existence of God, and God's "role" in the cosmos. He accepted many of Descartes' arguments, including his idea that while we may use the term "substance" to describe mind and body, they do depend on God to exist. Spinoza disagreed both with the notion of an immaterial mind, and a wholly material cosmos. He believed that not only did both mind and body depend on God's existence, but that they were in fact God's existence, manifested in substance. All of the cosmos is a manifestation of God's essence, and so there is only one substance, God, leaving no room for any substantive dualism.
By this theory, mind and body are one and the same thing - God's essence - but there is room for distinction, as, for Spinoza, they are different attributes of this essence. This dual attribute theory, also called dual aspect theory, seems to resolve Descartes' problem of interaction, because in Spinoza's model there is no interaction. As mind and body are manifestations of the same thing, they need not interact, because they simultaneously share the properties of God's essence.
But this raises its own problems! If everything that exists is the manifestation of this essence, how can one mind by separate from another? As it is quite obvious that we do not all share a very complete collective consciousness, our minds cannot be simultaneously sharing all of God's essence. It seems almost contradictory to suggest that mind and body share this whole essence, and yet different minds have only a subset of this essence. There must either be something external to God in which individuality can reside, or God's essence cannot be shared as a whole.
Similarly, it seems odd to suggest that music might be manifested in its physical and mental attributes, and for the physical attributes to be mutable, and the mental attributes to be immutable. For it follows from Spinoza's conception of God's essence that the essence is mutable, and attributes are immutable manifestations of this essence. So if one attribute seems mutable, then it must be the essence which is mutable, and yet how can the other attribute not be mutable? I cannot see a way to resolve this problem.
In The World as Will and Idea, Schopenhauer developed a slightly more sophisticated dual aspect theory. To begin with, he rejected the notion that God is at the centre of all things, wanting to remove what he saw as speculative theism from philosophy. He thought that the cosmos consisted of manifestations of a universal Will, much like Spinoza's essence, except that it was not God, and its manifestations were subtly different. Schopenhauer borrowed a distinction from Kant to explain the manifestation of the Will: he said that there were two aspects of the Will, nouminal and phenomenal. A nouminal aspect is a manifestation of the Will as it is in itself, independent of a conscious being's knowing it. A phenomenal aspect is the Will as it appears to a conscious being, in relation to our knowledge of its nouminal aspect.
So in the case of music, the nouminal aspect is the essential quality of that music, which is independent of our knowing it, and so to us it is immutable. The phenomenal aspect is then the various ways in which we can know this music, be it in sound waves, stored on paper or magnetic signatures, or any other manifestation. Our minds would then also have both nouminal and phenomenal aspects, and so they are both manifestations of the universal Will, but they do not necessarily simultaneously share the whole of the Will, and so the limits of our knowledge limit the phenomenal aspect, providing scope for separable individuals in the universal Will.
So Schopenhauer allows for a distinction between two kinds of aspect, whilst resolving the problems raised by Spinoza's theory. But his theory does leave the question of how this might fit into our understanding of the physical world, or what Schopenhauer would call the phenomenal world. For we cannot divorce the world from the dimensions of space and time. Substance must exist in these dimensions, as otherwise there can be no explanation for what we experience. Kant firmly believed that only the phenomenal aspects of the Will exist in space and time, and that the nouminal aspects and the Will itself exist outside of these dimensions.
So we might extend Schopenhauer's theory, and conclude that there exists a universal Will, and that in that Will there are discernible individual subsections, each representing something we see in our experiential world. As each of these subsections exist, they are manifested in nouminal aspects, about which we can have no knowledge. The cosmos therefore is a "mass" of nouminal aspects of the Will (I put mass in quotation marks because there is no word that can describe a collection of immaterial things). As conscious beings perceive these nouminal aspects, there pop into existence in our spacial dimensions phenomenal aspects of those subsections of the Will.
We, as individual consciousnesses, experience the Will most directly in ourselves, as our mind is the nouminal aspect of the Will, and our body is the phenomenal aspect of the Will, simultaneously aware of one another and yet with only phenomenal knowledge of oneself. Of others, we are aware only of their phenomenal manifestations, and they are manifested only when a conscious being perceived them. But they continue to exist, outside of spacial dimensions. Whilst this seems like a mind-boggling-ly complex conception of the cosmos, it seems the least objectionable, and coheres with experiential and rational evidence most closely.
Descartes, Meditations on First Philosophy, Cambridge University Press
Descartes, Principles, Cambridge University Press
Schopenhauer, The World as Will and Idea, (in J. Cottingham (ed.), Western Philosophy, Part III, pp. 160-164.)
Spinoza, Ethics, (in J. Cottingham (ed.), Western Philosophy, Part III, pp. 152-154.)
The ontology of the mind has puzzled philosophers and scientists for millennia, providing an unusual diversity of theories. However one theory, or rather one superset of theories, has dominated the discussion since Descartes first proposed it in Meditations. Despite its prominent place in the history of the subject, however, dualism has been the focus of many criticisms, some of which seem to suggest insoluble problems with the distinction between mind and body. These criticisms have, in turn, prompted philosophers to widen the scope of dualism from Descartes' original substantial dualism, creating theories whose objections are as unsubstantiated as the theories themselves.
Descartes' original dualist theory was based upon a few observations he made about the nature of our thoughts. In Meditations he claimed that the only thing about which he can be certain is that he exists, since otherwise he would not have been able to have that thought. From this he determined that he could clearly and distinctly perceive his self (his mind) as distinct from his body, and so suggested that the mind and body are two entirely different and distinct substances, which are closely conjoined so as to allow them to interact. Descartes offered various other observations to support his theory, such as that we may cut off a foot and still have our body, but that we cannot conceivably take away a part of our mind since it is an indivisible whole, and hence the two must be distinctly different kinds of substance. An important part of Descartes' writings on dualism are also based on rationalism, and his emphasis on the creation of knowledge through reason as opposed to pure observation, but such topics are outside the scope of this essay. Suffice to say that Descartes set-up the mind body problem in terms of two distinct substances that interact.
It is in this short definition that we find the most troubling problem with substantial dualism; how can two entirely distinct kinds of substance, material and immaterial, interact? When we talk of interaction between two substances, we generally do so in terms of physics, observable laws of nature, yet many have charged that physics has nothing to say about the immaterial, and that we know of no discoverable causal mechanism between the mind and body.
The first allegation is false, an out of date assumption based upon the Newtonian paradigm, and can be quickly discounted by pointing to work on multiple dimensions, gravity, and other such fields generally associated with quantum relativity. Indeed, the more physicists explore and theorise these contemporary problems, the more they begin to sound like dualists, or even idealists. In one leading theory, loop quantum gravity, things "do not live in space and are not made of matter. Rather their very architecture gives rise to space and matter" (Gefter, Amanda, Throwing Einstein for a Loop, Scientific American, December 2002).
The question of how the material and immaterial might interact is more difficult to solve, however; physics may have a lot to say about the material and immaterial but one cannot generalise based on a mix of conflicting and ever-changing theories. To sustain dualism, its critics charge, one must be able to point to a causal relation between a process or state in the mind and a process or state in the body that ?should in principle be discoverable? (Smith and Jones, 1986, p. 53). That no dualist has been able to do so is made all the more damaging by the fact that a materialist can quite easily provide an alternative explanation; that is that the causal relation between a thought and a resultant action is as simple as changes in one's physical state, in terms of neurological and physical relations and reactions.
But this picture looks less certain that its proponents claim, since the observations we can make may merely be correlations, caused by some other factor. For example, when a barometer needle drops, a thermometer might rise; does this show that one causes the other? No, because in this case, both are caused by an increase in cloud cover. In the same way, the patterns we can observe in the brain may merely correlate with the actions we see in the rest of the body, both being caused by an immaterial mind, or some other agent.
Besides, the fact that we have not yet discovered a causal relation that fits dualism does not mean that one won't be discovered, and hence one cannot say based on the lack of a discovery that such a relation isn't discoverable. Moreover, ?as Kant put it, experience teaches us that a thing is so-and-so, but not that it cannot be otherwise?. Therefore an appeal to monism based upon the lack of experience of the immaterial may be appealing, but it is not proof one way or the other. It does, however, leave us with problems that have no apparent solutions, unless our understanding of physics changes radically.
One can also question the intelligibility of the immaterial affecting the material, as many have done. However this again seems based upon an outdated understanding of physics that has been internalised since school, and is as likely to be due to a lack of understanding as to a lack of any truth in the suggestion. It might have seemed unintelligible to a mediaeval person that the world was a sphere, but we can be fairly certain now that that is true.
Ayer went further to suggest that the very idea of an immaterial entity is unintelligible. First, he said that if we are to call X an entity, we must be able to ask: ?how many Xs have we got??; in this way we can distinguish between, for example, a billiard ball and the property ?red?.One possible reply to this is that it is conceivable that we each have many minds, working together but giving the appearance of a single agent, just as a flock of birds may appear to have a group consciousness. There seems no conceptual reason as to why one cannot apply numerical properties to the immaterial. The many-minds possibility does raise a large number of other problems that monist theories needn't worry about, but again they are not problems that can be solved unless we can solve the problem of the existence and nature of the immaterial.
Ayer's second criticism was that we must be able to individuate between entities, in the way that we can say that two billiard balls are different entities. The only way that we can do so, when inherent physical and subjective properties are discounted, is to refer to their position in space-time, since no two entities can exist in exactly the same place at exactly the same time. If the immaterial does not exist in the dimensions of space-time, then we must ask how we can possibly distinguish between minds? It becomes equally possible that there is only one mind inhabiting many bodies and applying different characteristics to each, but that is not a theory that many dualists would want to sustain, so how can we show that we each have our separate minds, or that, to return to the many-minds theory, that we each have our own single mind? The only solution seems to be to demonstrate a much closer connection between mind and body than Descartes suggested, such that the mind and body share enough properties to be one-body-one-mind but without reducing to a dual-aspect theory.
A solution can be found in the answer to a further problem: at what point do you consider an animal to have a mind, rather than pure behavioural instincts? The materialists reply would be that it will depend upon the capacity of the central nervous system to hold experiences sufficiently complex to allow for consciousness, and psychological mechanisms to translate these into thoughts (in terms of language). In other words, particularly advanced configurations of matter can provide the means for consciousness. An analogous answer can be given by the dualist; that particularly advanced configurations of mind can provide the means for consciousness. But if the dualist is correct here, what of the correlation in the complexity of the brain? To reduce the brain to a mere physical container seems strange.
An answer can be found in property or panpsychic dualism, which hold that all matter has immaterial, mental properties, closely tied to the physical properties, so that particular configurations of mental or physical entities will necessarily entail a correlative configuration in the opposing property. This not only provides as unobjectionable an answer to the question of consciousness as the materialist's answer, but it also provides a close connection between mind and body, such that each individual will only have one mind, and one that can be individuated from other minds, by virtue of the fact that the mind is the configuration of the mental properties of the body. According to its original proponent, this position is ?an innocent version of dualism, entirely compatible with the scientific view of the world?since ?nothing in this approach contradicts anything in physical theory; we simply need to add further bridging principles to explain how experience arises from physical processes?.
No matter how innocent the position is, however, it does not solve, many of the problems associated with dualism. It cannot say with certainty whether or not matter has mental properties, nor how these mental properties might interact with the physical properties; as with all dualist theories, it can only offer conceivable possibilities, and contrast those with opposing monist theories with a view to making dualism seem more attractive. On the other hand, materialism is afflicted by many of the same problems, and many more of its own, and so it is not yet proven either. In other words, neither dualism nor monism are proven, and both are faced with tough problems, some of which may be resolved or tempered by the discoveries of scientists, and others which we are unlikely to ever answer, unless we discover a way to measure that which is currently unobservable, if indeed it exists: the immaterial.
But to say that the problems are tough is not to say that they are insoluble, rather that we are unlikely to solve them any time soon. In claiming that the problems of dualism are insoluble, one would be implying that it is a position that cannot be sustained, and that is a conclusion that cannot itself be sustained.
Chalmers, David, Facing Up to the Problem of Consciousness, Journal of Consciousness Studies, 1995
Descartes, Meditations on First Philosophy, ed. John Cottingham, Cambridge University Press, 1996
Hart, W. D., Engines of the Soul, Cambridge University Press, 1988
Heil, John, Philosophy of Mind: A Contemporary Introduction, London: Routledge, 1998
Smith, P &Jones, O. R, The Philosophy of Mind: An Introduction, Cambridge University Press, 1986
Behaviourism closely followed psychology in the early 20th century, and wanted to concern itself only with publicly observable events and processes in the mind. Along with psychological behaviourists, philosophical behaviourists wanted to resolve the metaphysical nature of the mind and show that terms gained from introspection like 'feeling', 'lived experience' and 'will' are either meaningless or can be boiled down to statements about publicly observable, physical events and processes.
They wanted to construct a semantic theory of the mind that would explain the meaning of mental terms, which could only be achieved by being able to verify if a particular term or statement was accurate or false. Since immaterial notions aren't publicly observable and verifiable, behaviourists concluded that psychology and the philosophy of mind should only concern itself with the material... i.e it is a physicalist theory.
Logical behaviourism therefore holds that any mental term can be understood in terms of observable physical processes or events. For example, if I say I have a toothache, a scientist should be able to point to a problem with my gums, the transmission of information regarding this problem through my central nervous system to my mind, and the characteristic changes in the chemical makeup of my brain. Conversely, if those particular physical events and processes were observed, a scientist would be able to say "he has toothache".
In other words, all meaningful psychological statements are translatable into statements which refer only to physical concepts, without any loss of content; all 'conscious experiences' can be reduced to mere behaviour. Psychological concepts, according to Hempel, serve merely to abbreviate "the description of certain modes of physical response characteristic of the bodies of men or animals" (Hempel, 1980, p.19)
Objection: One can feign a mental state (e.g. actors)
But according to Hempel (1980) a full examination of the central nervous system and other physiological conditions will uncover a feign. But then are there not mental terms, all of whose verifiable criteria can be feigned? In this case, Hempel says, the event or process must be genuine, i.e. if Paul shows all the signs of having the flu, then Paul has the flu.
Objection: How can physical tests capture the qualitative nature of an experience, i.e. what is is to be in pain? Surely such experiences are neither behavioural nor dispositional (e.g. being disposed to be angry), and so can have no physical basis? Even if they do have some physical basis, how can we be sure that the mental states exactly correspond with physical states?
This problem is further complicated by the presence of other people. Let's say I experience the sensation of the colour red, and I find that correlates with a brain state X. Another person then says they are also experiencing the sensation of the colour red, and again we find the same correlation in their brain state. One might conclude from this that the two correlations point to an obvious connection. But how can I know that my mental state is the same as that other person's? Our descriptions might coincide whilst our actual mental states are qualitatively very different, suggesting no connection between mental and brain states, or at least no simple correlative connection.
Behaviourists have no satisfactory response to this objection, since they are interpolating the nature of the mental and brain states from the relationship between inputs and outputs, and so can say nothing of the nature of those states themselves if they are qualitatively different but produce the same measurable behaviour. Wittgenstein discussed this problem by way of the 'beetle in the box' analogy:
(paraphrased)Suppose everyone owns a box, and in each box they keep a 'beetle'. Nobody can see inside anyone else's box, nor know anything of its contents, except that its owner says it contains a 'beetle'. How am I to know my 'beetle' is the same as your 'beetle'? If people then used the term 'beetle' in their language, it couldn't refer to any physical object, and so would, gramatically speaking, drop out of consideration. (Wittgenstein)
In other words, not only can we not know anything about these qualitative experiences, they must in fact be considered non-entities, and so any attempt to explain mental states and processes in physical terms merely through demonstrating correlations in input-output scenarios will be completely flawed.
Though logical behaviourism must be wrong about a lot of things, it does correctly identify the non-contingent, conceptual connection between mental and behavioural descriptions. We learn mental concepts in their application to behaviour, and mental phenomena can often be individuated by their behaviour rather than by their subjective internal features. So there does appear to be a strong connection between behaviour and some mental states and processes, but suggesting that behaviour is all that they are seems far fetched.
Indeed, we can know about our own mental states without needing to observer our behaviour, and often without even observing our own mental states; I know I dislike Big Brother without need for any kind of observation. So logical behaviourism is either asymmetrical in terms of how it suggests we understand mental states and processes, or simply unnatural. This criticism was further developed by Malcolm, who pointed out that if one really were a logical behavourist, one would see people's emotions and mental states merely as physical alterations in the three dimensions, and so one wouldn't see someone as being angry, but as having a particular face. This is enough to know that we aren't logical behaviourists.
Finally, one can undermine the behaviourist thesis by arguing from regress. Suppose a logical behaviourist wanted to explain my belief that it is about to rain. Perhaps I bring the clothes in off the washing line, or put on my coat. To explain that behaviour, the logical behaviourist must make further reference to my belief that I will get wet if I don't put my coat on, and my desire not to get wet, and all in terms of behaviour. Clearly to explain the beliefs and desires, the logical behaviourist will have to go in circles, or run out an extremely long string of behavioural explanations without ever leaving mentions of psychological terminology in the final explanation. It would seem that the ambitions of the reductionist, trying to reduce all psychological terminology into verifiable behavioural terms, are simply too ambitious.
C.G.Hempel, 'The Logical Analysis of Psychology' [originally published in 1935], as reprinted in N.J.Block (ed.), Readings in Philosophy of Psychology, Volume I, (London: Methuen, 1980), p.16
Identity theory is a kind of materialism developed as a reaction to work in psychology and the physical sciences in the mid 20th century. It essentially boils down to these statements:
1) Minds are identical to brains
2) Mental states are identical to brain states
3) The realm of the mental is a subset of the realm of the physical
Proponents of this theory state that this claim is a contingent fact about the nature of the mind and the brain; it makes no attempt to explain the meaning of mental terms and so isn't a semantic thesis like logical behaviourism (e.g. 'pain' means physiological state X).
One identity theorist, Smart, claimed that it ought to be a strict identity statement. By this he meant that mind and brain refer to exactly the same thing, i.e. if minds are identical to brains, then brains are identical to minds. Strict identity statements are therefore logically symmetrical. An "un-strict" identity statement would be assymmetrical, for example: rain is identical to bad weather, but bad weather could be rain, sleet, snow, etc.
Identity theory is deemed to be contingent because of the history of the theory. Generally, necessary facts are deemed to be a priori, and so discoverable through study of language, e.g. "one plus one equals two", or "a bachelor is an unmarried man". But because identity theory came from scientific discoveries, the thought is that it cannot be necessary. But then if two things are identical, must that fact not be necessary? One cannot say that in conscious beings on earth, their brains are identical to their minds, but that it is possible that that wouldn't be the case, since that contradicts the theory.
One can however point out that the strength of gravity at the earth's surface is a necessary fact, and yet we only discovered that after thousands of years of scientific investigation. Necessary facts needn't be a priori facts accessible through analysis of language.
Type-type or token-token?
One problem that arises from identity theory is just how identical these two states, mental and brain, are. There are two kinds of identity theory one can subscribe to:
1) Individual mental states are identical to individual brain states (token-token identity theory)
2) Types of mental states are identical to types of brain states (type-type identity theory)
Type-type identity theory would hold that if my mental state for seeing red, X, were identical to my brain state Y, then whenever I saw red I would always have mental state X and therefore brain state Y. In other words, conscious experiences can be categorised into types, each with its characteristic mental and brain states.
Objection: the brain is labile (open to change), type-type identity theory seems difficult to maintain. For example, if one part of my brain is damaged, my brain will often route around this problem, resulting into two different brain states for ostensibly the same mental state. The context of a mental state also seems important, since the mental state of an experience of red may result in an entirely different brain state if I am feeling hot or cold (not least because of the related symbolism).
This becomes especially problematic between different brains. If I share the belief: "the capital of Italy is Rome", with another person, must our brain states be the same? What do we mean by brain states here? An analogy with a hard drive might be useful, since a hard drive may store the data in any number of ways across the surface of the disc, whilst still retaining the same information. Are all these many combinations of possible storage states to be considered as a single information state? If so, then the many ways in which a mental state may be represented in brain states may all be considered to be the selfsame brain state.
But is this not beginning to sound more like token-token identity theory, in which each mental state is said to be identical to an individual brain state, allowing for no generalising categorisation, but still not explaining how one can have a logically symmetrical identity statement when one single mental state can have many different brain states. That is unless one can claim that each different brain state means that there is an entirely different mental state.
Realisibility and species problems
Obviously, humans aren't the only species that can realise consciousness and therefore mental states. Given that this is the case, type-type identity theory must either be rejected or become species-specific. For example:
Human mental state X is identical to human brain state Y
Gorilla mental state X is identical to gorilla brain state Y
Human mental state X is not identical to gorilla mental state Y
etc.
This one retreat for type-type identity theorists opens up a can of worms though, since it again begs the question: should one not take into account the physical nature of individual brains, the contexts of mental and brain states, the age of the subjects, etc? In this case, one either draws up an extremely long, comprehensive list of possible mental-brain states, or one admits token-token identity theory.
A final objection
There is one thing identity theory still has little to say on, however, and that is: what is it to have a particular conscious experience?. To answer what it is to be in pain, an identity theorist might look up you in a table and find the corresponding physical properties of the brain, or simply the latter, and tell you that to be in pain is to have a particular physiological state. But does that tell us all there is to know about pain? It somehow seems unsatisfactory.
http://www.seop.leeds.ac.uk/entries/mind-identity/index.html
What follows is my essay on this topic:
Central state materialism, the dominant branch of identity theory, grew out of a desire in philosophy to explain mental phenomena in terms of the material sciences, which in turn was a result of the growing potential in the mid-20th century of the neurosciences. Its central claim is that all mental phenomena are physical phenomena, identifying thoughts, beliefs, dispositions and other mental states and processes with events and processes that the neurosciences can study in the brain. But although may at first seem commonsense, central state materialism fails to provide a framework by which we can understand most mental phenomena, and when scrutinised in this light it is clear that it also makes next to no sense at all.
First, we need to understand the theory itself. Learning from behaviourism and its objections, U. T. Place made the extraordinary claim that mental processes can be identified with brain processes in the same way that lightning can be identified with an electrical discharge; when we speak of a thought and of a particular brain state, we speak of exactly the same thing but in different terms. Because this identity theory is usually proposed by materialists, and because what philosophers call 'brain', neuroscientists call the 'central nervous system' (CNS), this theory is often called central state materialism (CSM).This means that all mental states are identical to CNS states, so that if one were to say "I can see an ostrich", one could identify that state with a particular state in the CNS and say that that thought is a particular neurological state and nothing more. To put it in perspective, since the idea that a thought might be reduced to a few neurons doesn't seem too odd, a CSM would have to hold that the phenomena known as 'loving one's parents' can be similarly reduced to certain material phenomena in the CNS.
Note that CSM says nothing about what it means to love one's parents, nor what it is like to have that experience; it is simply a statement of fact, that that is the ontology of the experience. This in itself seems like a shortcoming, since if we are to reduce all mental concepts to physical concepts and in doing so demonstrate that they are identical, surely we must be able to provide physical explanations or descriptions for concepts like 'what it is like to love one's parents'? A CSM might reply that one can say simply that what it is like can again be explained in terms of the CNS states and processes that are identified with the sensations caused by the experience; that an explanation of what it is like to experience mental state X and what that mental state X is are different needn't invalidate CSM, since we can find parallels in everyday language that we find unobjectionable. For example, I might refer to "the table", by which I mean an object with legs on which I can rest other objects; I might also refer to "that lump of wood", by which I mean an object created out of pieces of wood that sits in my room. Though each statement appears to refer to different physical concepts, they each refer to the selfsame object, and so a CSM can claim that one can reduce all mental concepts to material concepts, even if this seems counter-intuitive.
A general problem that any counter-intuitive theory brings up is that it must be contingent, since if it were necessary, we should have been able to discover it through analysis of language rather than through scientific discovery. Its contingency suggests that it is tied to a particular understanding of physics, in this case a materialist account of reality. Smart, one of the leading proponents of identity theory, thought this didn't matter: "there can be contingent statements of the form 'A is identical to B', and a person may well know that something is an A without knowing that it is a B" (Smart, p. 58) He further defended the materialist conception, stating that "there does seem to be, so far as science is concerned, nothing in the world but increasingly complex arrangements of physical constituents" (Smart, p. 53) By physical, of course, he means material, since if physics were to posit the existence of immaterial substances, they would become physical. But this is not a good reason because it is based upon a field of study that conceptually limits itself to the physical (neuroscience), and so will inevitably provide a physicalistic view of the cosmos. That we can provide physicalistic explanations of things does not mean that those things are wholly physical, just as my explaining the exchange of information over a network in terms of bits and processes doesn't mean that there is nothing more to this thing, because if we look we can also explain it in terms of sub-atomic particles in cables and circuits. What it does suggest is that we don't need purely mental concepts to explain mental phenomena, and so it makes sense to stop at material explanations rather than speculate about immaterial concepts for which we have no empirical evidence.
Or so Smart and colleagues thought back in the 1960s. If we were to start from scratch and write an account of the mind/brain problem framed in terms of contemporary science, it might look quite different. For example, since in introduction and development of string theory from the 1960s, we can now, within the confines of acceptable theoretical science, suggest that reality is composed of 26 dimensions, 22 of which are so tightly wrapped up in our four dimensional spatial-temporal reality that they needn't have spatial or temporal properties. This allows for effects like gravity and quantum effects like action at a distance to be described in terms of the interaction of spatial and non-spatial 'things', and so conceivably the mind could be an immaterial thing wrapped up in our four dimensions and in some way closely connected to our CNS. In this case, physicalist identity theorists must commit themselves to the possibility of dualism, leaving central state materialists cohering only with the larger, more proven subset of scientific theory.
A materialist identity theory also introduces a question of how we locate thoughts in our CNS; though we never imply or apply any spatial properties when using mental terms, according to CSM "we must begin to locate thoughts in the head". But how can we do this? According to Malcolm, Smart's criteria for strict identity are that "if x occurs in a certain place at a certain time, then y is strictly identical with x only if y occurs in the same place at the same time". But this is impossible to test empirically, since if we locate a particular CNS process in the CNS, then how do we separately locate the mental process in the exact same location? Not only is it impossible, but it is also unintelligible (Malcolm, p. 174), therefore we must conclude that identity theory can be nothing more than a hypothesis, an irony considering identity theory's emphasis on the material sciences.
Furthermore, it is questionable whether or not the material sciences are compatible with identity theory. When I have a sudden thought, that mental process has what Wittgenstein called 'surroundings', the circumstances that contributed to the formation of the thought. To borrow Malcolm's example, my thought that I need to take the milk bottles out may be tied to the circumstance that the milkman is about to arrive. According to Smart's strict identity theory, CNS processes must also have these circumstantial properties, but these cannot be explained in terms of physics; one couldn't explain the milkman's arriving soon in terms of physical properties of the CNS.
Further problems with CSM arise when we analyse the two varieties of the theory: type-type CSM and token-token CSM. According to type-type CSM, types of mental states are identical to types of CNS states, e.g. every time I think 'that is a table', we have a mental state X that is identical to CNS state Y, and that state is always the same, every time I have that thought. This is quite obviously ridiculous, not least because of context, but also because of the lability of the CNS. We can say, for example, that one time I think 'that is a table' I will be looking to lay some cutlery, whilst another time I have that thought that has the selfsame description in language, I may be looking to buy a chair in a furniture store. Each time the thought seems the same, and yet it makes sense that the CNS state would be quite different because of the context. And what if the part of my CNS that deals with that thought was slightly damaged? Neuroscience tells us that the CNS will often be able to route around the damage, creating an entirely new CNS state for the same mental state.
Type-type CSM creates further problems when you consider the differences in individual's brains, and the fact that other species can have conscious mental experiences with completely different CNSs. For the theory to work and avoid species chauvinism, we would have to create a complex table listing, for each type of CNS, their characteristic types of CNS states, and then identifying these types of states with types of mental states, which seems extraordinarily complicated. In fact, it begins to resemble token-token CSM, which holds that though every event or process may be different, for each token mental state there is an identical CNS state. This resolves all of the problems associated with type-type CSM, and can be well explained by analogy. We can store information in many different ways, be it in a bit travelling over a network cable, as a magnetic signature on a hard disc, an indent on a CD or an ink mark on paper. According to token-token CSM, as each different form of storage is entirely different, so the information in each case must be different, such that the information stored in the ink mark is identical to that ink mark, and the information stored as an indent on a CD is identical to that indent, but those two bits of information are slightly different, each perhaps containing the nuances of context and the state of the CNS at the time.
But even accepting this resolution, we still find ourselves unable to provide a scientifically intelligible account of that CNS state since we are unable to make reference to nuances of context. And even if we did, we would not be providing any reason to accept CSM, except that ontologically it doesn't posit anything that we don't know about empirically, and so is the simplest. Perhaps in a completed neuroscience we will be able to provide material-material explanations for all mental concepts, and we will resolve the problems in physics returning to a purely materialistic reality. But then CSM relies entirely on a weighted possibility, and at the same time is fraught with conceptual and ontological problems. We have no reason to believe that neuroscience will be able to tell is 'what it is like to love one's parents' nor 'what it means to love one's parents'; trying to show that something so complex as a thought with surroundings can be reduced to something explicable in terms of physics seems wrong; suggesting we can categorise mental experiences seems chauvinistic and naive; positing the identity of token mental states with token CNS states seems to do no more than highlight the close relation between the two. In other words, CSM does little to enhance our understanding of the relation between the mind and the CNS, and is so riddled with problems that it quite simply must be wrong.
Gefter, 'Throwing Einstein for a Loop', Scientific American, December 2002
N.Malcolm, 'Scientific Materialism and the Identity Theory', in C.V.Borst, The Mind/Brain Identity Theory, 1970
J.J.C.Smart, 'Sensations and Brain Processes', in C.V.Borst, The Mind/Brain Identity Theory, 1970
Functionalism emerged in the 1960s from cognitive science, and replaced identity theory and central state materialism as the dominant philosophy of mind. It was developed mostly within the materialist tradition, and is therefore generally considered to be anti-dualist, though this is not necessarily a feature of functionalism.
Functionalism first emerged as a criticism of type-type identity theory, claiming that it was wrong to locate mental phenomena in matter because that implies:
1) Mental phenomena can only be had by beings with a central nervous system similar to ours
2) Beings with similar central state nervous systems must have similar mental states
Functionalism developed the idea that mental phenomena can be had by beings with very different physical constitutions (e.g. humans, cats, computers), and that the same mental phenomena can conceivably be had by physically different beings.
Functionalism's central thesis is that mental phenomena depend not upon the matter in which they 'reside' but in their organisation; i.e. mental states are functional states. A functional analysis of mental phenomena would therefore explain the working of the component parts, or functions, of a psychological organism, and their overall organisation. The mind could therefore be explained in terms of (admittedly complex) flow charts. The mind, and mental faculties, are defined in terms of what they do, rather than what they are, just as one would define 'crank shaft' as 'something that opens and closes valves', rather than identifying the definition with a particular physical object.
Functionalism solves one of the most damaging problems of behaviourism, which is that one could have two stimuli cases providing quite different responses, or indeed several cases of the same stimuli-response relationships with different associated mental states. With functionalism, having the same inputs and outputs needn't mean having exactly the same mental phenomena, since the functions that process the inputs and provide the selfsame outputs can differ. This implies quite a startling conclusion: if one could map out the entire functional process of one thought, one could make a computer 'think' in an identical fashion, and so it is quite conceivable that a machine could love a human, and vice versa.
On this theme, functionalism can be summed up as follows: mind is to brain as software is to hardware. Two systems can be computationally equivalent by physically different.
Is functionalism dualist, materialist or idealist?
By defining itself in terms of function rather than in terms of its substantial instantiations, functionalism remains ontologically liberal (identity theory was thought to be 'chauvinistic') and so avoids the problems of what kinds of beings can have mental phenomena, and of dualism. Functionalism could be considered compatable with a very liberal token-token identity theory, however, as one could claim that each mental state is identical to a particular physical state (e.g. my pain Y, happening right now, is identical to brain state X) but that mental states in general needn't be thought of as identical to physical states in general (e.g. pain Y is always identical to brain state X). An identity theory this liberal, however, without the additional ideas of functionalism, becomes more or less meaningless as nothing that it can tell us can ever be proven in any sense (in positing an identity one needs to be able to know of each honomonous entity distinctly, and show a pattern of coincidence with reasons why it is more than coincidence; here one can find no pattern).
It is this distinction between functional states and physical states that leaves functionalism open to forms of dualism, in particular property dualism. Mental phenomena can be thought of as functional properties of brains, with sufficient detachment for entirely different functional states to be associated with the same physical state, and vice versa. In fact, it is conceivable that functionalism might fit with idealist theories. There are no contradictions in functionalism in supposing that a conscious being might have a mind but no brain, and so it is logically possible. Materialism cannot therefore be considered a conceptual truth based on functionalism alone.
Functionalism and consciousness
According to functionalism, one might be tempted to say that a conscious system is a computational system that is capable of posessing functional properties. If we consider Bill Gates, aside from his obvious physical properties, the kinds that any physical thing might have (e.g. his weight, height, his particular chemical composition), one can attribute various properties to him: he is Chairman of Microsoft; he is a computer programmer, etc. Each of these properties are functional properties, and by virtue of having them he is conscious.
Of course, going by that definition, a pocket calculator could be said to be conscious. So it seems that to answer the problem of consciousness, functionalism needs more than a theory of functional processes and properties. Intuitively, consciousness seems linked to the ability to posses functional properties that are capable of producing qualitatively different mental phenomena, what some philosophers refer to as qualia.
But it seems entirely possible, and coherent with functionalism, to suggest that two people could experience entirely different qualia with exactly the same equipment, e.g. two people with the same visual "equipment" could see a block of colour; one could see "red", the other "green" (putting linguistic considerations aside). This phenomenon is known as inverted qualia, and poses no problems for functionalism as such. In fact, in Inverted Earth Ned Block pointed out that one could conceivably render someone unconscious, invert their visual equipment and put them into a room that is identical to that of a second person except that all colours are reversed; in this situation, their qualia would be identical, since what it would be like to experience the colours would be identical for both people, despite their hardware and the reality they are seeing being opposite to one another.
However Block also raised several problems with qualia that affect functionalism in particular. The first is to say that if we accept that inverted qualia pose no problems to functionalism as such, then we must also accept the logical possibility that my visual qualia in a given situation might be identical with your auditory qualia in a given situation, since there is no necessary connection between qualia, the person's hardware and the environment that is 'causing' the experiences. This is both perplexing and attractive to those who feel materialism to be too inhuman, since it suggests that my listening to Beethoven's 5th symphony and your reading a novel set in the Napoleonic wars could evoke exactly the same mental phenomena; what is is like for me to listen to the music could be identical to what it is like for you to read the book. Romantic as this seems, it does make explaining functional states and properties extremely difficult, as you can no longer use the hardware nor the environment as a reliable reference point.
There may also be mental states that aren't public, such as unconscious states, and so that functionalists cannot accurately describe nor explain, at least not objectively, since they cannot get any reliable information by interacting with the owner of the states, they can't look at the brain states, and they can't rely on the subject's environment.
One can also posit the existence of zombies, unconscious beings that have the same behaviour and the same brain states as a conscious being, but no qualia. The functionalist ought to be able to distinguish a zombie from a conscious person, but given that all of the public information seems identical to that of a conscious person, how could one ever know? How could we know everyone else isn't a zombie, or that we ourselves aren't zombies? By being so liberal about qualia and their relation to the brain and the subject's environment, functionalism solves a lot of the problems associated with behaviourism and identity theory, but it also opens the door to extreme forms of scepticism, and makes it extremely unlikely that it could deliver any scientific explanations of the functioning of a specific mind-brain.
Commonsense psychology developed out of functionalism, in a move to explain how functionally equivalent beings (e.g. me at age 2 and me at age 20) might exhibit different kinds of behaviour, and why some beings might be considered whilst others wouldn't despite seeming to be functionally or behaviourally equivalent. Central to this philosophy is Jerry Fodor's Representational Theory of Mind (RTM), which postulates a system of symbols that function as mental representations, and which in turn consitute as a whole a language of thought.
What differentiates conscious and unconscious beings? A functionalist would say that conscious beings have beliefs and desires that cause behaviour, whilst an unconscious being acts upon "hardware" reflexes. According to adherents of the RTM, this is the only way to explain and predict behaviour; neuroscience can't say anything on this subject (at the moment).
Intentional realism and RTM
The central question made here is: how can mental phenomena be "about" someone, e.g. the sentence "Aristotle is dead" is about Aristotle and so intends 'Aristotle' in some way. How can mental phenomena and symbols be about things, particularly if one assumed materialism and more so if the thing the phenomena and symbols are about doesn't actually exist, e.g. a unicorn. It would seem that if we are to grant mental phenomena any intentionality, we must explain how they can relate to other things that may themselves be mental or non-mental phenomena.
According to Jerry Fodor, if I believe A, then the representational content of the belief is A, no more than a sentence. Intentional mental states are therefore relations to sentences that organisms stand in. We can only understand intentional states if we accept that beliefs and desires are real, and that they represent intentional mental states in the form of sentences in what Fodor called the language of thought.
To extend the computer analogy, the language of thought is like the binary machine code understood by the hardware. It exists between the hardware and software as a way of representing the machine's states in a form, or syntax, that is understandable for humans, and that can be translated into more human-readable languages. Thus my forming a belief that "it is cold" is a matter of my body 'feeling' the cold, forming a belief that it is cold in a sentence in the language of thought that acquires an appropriate functional role, and then possibly translating this belief into the English language, "it is cold".
The language of thought is a system of representation, and is said by its proponents to be the only way that we can possibly understand how a mind that is understood as a higher level entity could systematically correspond with bodily functions, hence the term "commonsense". It provides both semantic (substance) and syntactic (form) parallels between thoughts and "human language" sentences (e.g. English, French, etc.) that cannot otherwise be posited.
The language provides us with a semantic engine, a tool that can interpret the syntax of thoughts and of human languages without regards to their semantics (substance/meaning) and represent them in an appropriate fashion, retaining the semantics in the same way that a programming language might manipulate data based purely on the syntax of the code, without needing to know the content of that data. This semantic engine needn't understand the information it processes - it is intelligent in the sense that it performs operations or functions - but it contributes to an understanding in the mind, in that it enables the higher level entity to work with representations of bodily matters and with beliefs in a common syntax. John Searle, by means of an analogy called The Chinese Room, proposed that the mind shouldn't be thought of as understanding its functions any more than a computer might understand its own functions; this suggests that a machine might be understood to be as intelligent and conscious as a human, with immense consequences for our understanding of consciousness, in particular related to the Turing test. As such his views have generally been thought of as begging the question, and worked around or refuted by many RTM functionalists.
A further question arises related to the semantically neutral syntax of the language of thought, and that is this: what gives sentences in the language of thought their meaning? If we are to stick to the computing analogy, then in code an object could equally refer to, for example, a banana or an apple, thanks to its semantic neutrality. But at some point in the language of thought a particular symbol (object) must have a meaning, it must take on semantics. The RTM assumes that symbols do not have intrinsic meanings, and that their meaning depends upon how they are deployed, but that suggests that symbols in our language of thought only have meanings insofar as we assign them meanings, which, if true, means that the language of thought cannot explain how we can have meaningful thoughts, since the assignment of meanings presupposes meaningful thought.
If meaning is neither intrinsic nor interpretively assigned by the thinker, where does it enter this picture of the mind? The only answer, though liberal, is to posit that symbols owe their semantics to their relation to the mind's surroundings, e.g. a symbol 'banana' takes on meaning when it relates to a banana the thinker has come across. Thoughts, therefore, are the composition of symbols in the language of thought and their relation to the external world.
According to Noam Chomsky, if language is both productive and creative, then it can have no theoretical limit, and therefore neither can thought. This is a startling syntactic parallel, suggesting that our 'hardwired' langugage of thought adapts and evolves within us, and with the species' evolution. But if this is the case, then by our late age we must each have quantitatively different languages of thought that we each attempt translate into our native tongues. How then do we communicate so well, if our mental representations of our surroundings can be so qualitatively different? I would move to suggest that the differences in our languages of thought are in fact slight when compared to the unity between people's languages, and that these differences manifest themselves in subtle qualitative differences in our representations of our surroundings, different enough to allow for conflict of opinion and misunderstandings but similar enough to allow for common reference points. Perhaps this evolution of languages of thought also relates to culture, and cultural relativism?
This raises a further question of native tongues; could the language of thought in fact be English, Spanish, Latin, or any other 'human language'? fodor thought not, that it ought to be labelled mentalese, a universal language of thought. Chomsky agreed that it must be universal, since different cultures with no contact share such commonalities in their behaviour and mental functionality that they must share a common mental frame of reference.
The RTM can help us understand learning and understanding. Concept learning can be understood as involving operations of hypotheses, testing, representing test results and forming conclusions. This process is most naturally performed and described with language, which suggests that there is nothing more to learning and understanding than our commonsense perception of the processes. When we hypothesise, we are forming connections between mental sentences, creating structures from objects that can then be tested against surroundings, and so on. As we learn and understand, different mental objects take on different functional states in the process.
Objection: Need the language of thought be a language? Can it not be comprised of other kinds of data structures, for example images? Since we take in information in many different forms (visual, aural, sensual, etc.) doesn't it make sense that our minds process each form of input in a different way, and stores and represents these processes and states in different ways? It is possible that all data is broken down into linguistic structures, just as computers break down all data, be it music, art or writing, down into text-based data and ultimately into binary code, but these structures no longer have obvious linguistic qualities. We could only understand the language of thought therefore as something similar or analogous to binary machine code, which universalises all data for computers.
It certainly seems more sensible to posit a linguistic mental system than a visual or aural one; to represent all data visually, the mind would need to be able to break down all information into a common visual 'format' that could not be confused with any immediate visual data, e.g. it would need to break down the sentence "hello there", the noise of a cat's meow and Monet's water lillies into one single system of visual representation that didn't resemble some raw visual data we might otherwise see in the world. Though it would be possible, it is harder to imagine than a language that can do that, and to come up with such a visual sytem of representation we would most likely naturally use language of some form (even be it mathematics) to work it out, suggesting that intuitively we turn to language for sophisticated manipulation of data.
According to followers of Wittgenstein, there are many more objections to the RTM:
Objection 1: Thoughts are neither simple nor complex; they cannot be broken down in the same way as sentences
Objection 2: Thinking isn't a process; talking and using sentences are
Objection 3: Thoughts can be entirely instantiated in an instant; sentences take time to use
Objection 4: Talking is a form of behaviour; thinking isn't
Broadly speaking, they contend that Fodor and his followers misrepresent thoughts and language, falsely asserting similarities. Followers of RTM reply that thoughts do take time, for example when surfacing from the unconscious, or when being formed as the mind learns of new ideas and forms new mental connections that can over time be understood as one thought.
Tropisms also pose a problem for functionalists in general and therefore also followers of the RTM. A tropism is a being whose behaviour is genetic, or hardwired, with no flexibility and no thought, but that, in terms of its behaviour and all other publically observable phenomena, appears intelligent. The distinguishing difference between a conscious being and a tropism, or unconscious being, seems to be the ability to process new information and adapt. Fodor suggested that to be conscious, a being must have the ability to represent states of affairs and to act upon these representations. This answer reinforces the importance of representation in the understanding of our mind.
Finally, one can ask: even if the RTM is correct, how can we ever know of the language of thought that underlies all human language that we can actually study? It would be a matter of reverse engineering a code based on human behaviour and the goings on in the brain, either a daunting or an impossible task.
Donald Davidson wanted to resolve what he saw as a conflict in all materialist philosophies of mind, and in particular with identity theory, in the idea that mental phenomena have a causal role, and yet physical science has no need to refer to the mental. The problem stems from three plausible principles:
1) The Principle of Mental Causation: At least some mental events interact causally (directly or otherwise) with physical events
2) The Principle of the Nomological Character of Causality: Where there's causality, there must be strict laws
3) The principle of the Anomalism of the Mental: There are no strict laws on the basis of which mental events can be predicted and explained.
(1) and (2) seem to imply that some mental events can be predicted and explained on the basis of laws. (3) explicitly denies this. Davidson accepts all three and tries to show they are compatible. To this end, he presents a version of the identity theory which shows how the three principles can be reconciled, anomalous monism. It is 'monism' because it entails that there is only one kind of thing, the physical. However, it's not a type-identity theory. Anomalous monism postulates token event identity without psychophysical laws.
From the three principles above, Davidson categorises three possible positions in the philosophy of mind:
Nomological monism - there are correlating laws between the mental and the physical, but they both come under one category (either entirely mental or entirely physical)
Nomological dualism - there are correlating laws between the mental and the physical, and both are ontologically distinct
Anomalous monism - there are no correlating laws, and not everything can be explained in terms of the physical; but at the same time all events are physical
Davidson's new position allows him to avoid the reductionist problems associated with token-token identity theory whilst sticking to a strictly materialist conception of the mind. It allows him his next move, which is to insist that causality and identity are relations between events themselves, and that the study of the mind is the study of mental events, themselves purely physical but not explicable in terms of the physical. This allows him to avoid a further problem of identity theory that is intentionality, for all mental events cannot be understood purely in terms of their physical nature since one also needs to understand how these events stand in relation to each other and their surrounding circumstances.
Davidson holds that events can be described in different ways, and that events can only be related to one another given a specific description. Causality between mental events therefore need not be explicable in physical terms, and in fact Davidson denies that this is possible. So for example, if I have just read a book by Graham Greene I might reach up to the bookshelf to find another Greene novel; those two events are causally related and can explained by a strict law relating mental events, but there is no physical law that can link the brain states at the time of each event, nor of the physical events themselves.
This denial of psycho-physical laws stretches so far as for Davidson to assert that general principles of rational discourse associated with the physical sciences, e.g. coherence and consistency, need not apply to discourse of mental events, such that although correlations between the mental and the physical can be shown, they needn't be able to form strict laws of the kinds we associate with the physical sciences.
Davidson is thus saying that the mental supervenes on the physical, in that the mental is dependent upon the physical without, in linguistic terms, being strictly identical with the physical. That is to say that there cannot be two identical physical events with two different associated mental events, nor that a mental event cannot occur without a correlative physical event, but that an event might occur in the brain that cannot be explained satisfactorily in physical terms and that requires explanation of the mental event. That one set of events or facts, A, supervenes on another set, B, doesn't entail that A-events can be reduced to B-events, either by law or by definition. All it means is that the latter kind of facts fix or determine facts of the former kind.
Daniel Dennett advocated an approach that seems similar to Davidson's, in that they both attempt to resolve the problem of reductionism within the materialist tradition, and that they both disagree with Fodor. Unlike Davidson, however, Dennett advocates an extremely weak, or liberal, interpretation of intelligence, ascribing it to almost anything that we usually ascribe beliefs and desires to, even if those may appear to be linguistic, e.g. metaphors.
Dennett says that to be defined as intelligent, i.e. to have a mind, it must simply be useful for us to regard it as having a mind. So where in language we refer to things as though they act upon beliefs and desires, we should consider them to have minds, since it is useful in explaining their and our behaviour that way. For example, if a cat believes that some chicken is a good meal and it is hungry then the cat will eat the chicken. It is useful to ascribe a mind to the cat, and regardless of whether or not we think that cat might actually have the physical and mental faculties to process such mental states, we should consider it intelligent.
This instrumental kind of intentionality, according to which we understand minds by their relation to the things they have beliefs and desires about, has some far reaching consequences that Dennett is quite comfortable with. It means, for example, that we must consider plants to have minds, since it is useful for us to talk of a tree growing roots because it believes that water can be found at greater depths and wants water to grow. Similarly, a printer has a mind since, when the "Low ink light flashes", it believes the printer is running low on ink and wants you to know. One would say in response that here we speak metaphorically, imposing a set of antrocentrist linguistic concepts upon our surrounding world to make it more understandable. But Dennett disagrees, and insists that ascriptions of minds to all of these things is no more metaphorical than it is to ascribe beliefs and desires to human beings.
Dennett's ascriptivism lies somewhere in between two opposing positions:
"in the head realism" says that brains may be analogous to common man-made computational devices, e.g. audio cassettes aren't normally understandable, but given the correct hardware they are.