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Oliver Leech

Responses to the Doctrine of Mind-Brain Identity


To be in pain is, for example, is to have one's c-fibres, or more likely a-fibres, firing in the central nervous system; to believe that broccoli will kill you is to have one's B(bk)-fibres firing, and so on.
The Blackwell Companion to Philosophy:Chapter 5 'Philosophy of Mind' by William G. Lycan

The theory or doctrine of mind-brain identity, as its name implies, denies the claim of dualists that mind and brain (or consciousness and matter) are distinct substances. The tradition of dualism, whose clear-cut foundations laid by Rene Descartes (1596-1650) were built upon during succeeding centuries, sharply distinguishes between the stuff of consciousness and the stuff of matter. An outline of the position of the dualist will give a context for the identity theory.

To the dualist, mind is immaterial and, furthermore, cannot in any conceivable circumstance be reduced to matter. This irreducibility, to make the point more explicit, is not contingent on the level of progress of scientific investigation; the thoroughgoing dualist denies the possibility, however remote, that neuroscience, however sophisticated in future millennia, might ever discover that states of mind are the same entities as states of the brain. Why is the dualist so confident in his assertion? He argues that the very nature of consciousness is alien to that of matter of which the brain is composed. Material objects can be broken down into their constituents, to molecules, to atoms, to sub-atomic particles; they have mass and volume; they have dimensions (what Descartes called extension) and location. In contrast, mental states have none of these properties: sensations, feelings, thoughts (or any instances of mental states) are not divisible, they cannot be weighed and, occupying no space, have no position in space. Scientific investigation by the rules of its own procedures is limited to the study of the physical, the spatial, the quantifiable, and thus can never come into contact with the non-physical, the mental.

This is the doctrine which the mind-brain identity theory denies and seeks to refute. Its counter-claim is that mind and brain are one and the same entity, in short, that mental states are brain states. Why, then, from this perspective, has the dualist been mistaken? He may have been confused into believing that one thing is two things by the fact that it has two names. For example, while the Morning Star and the Evening Star appear by their different names to denote different things, in fact, astronomical studies reveal them to be the same (in fact, the planet Venus). Water is a different name from H20 but there is no difference at all in the physical substance which both names label. Scientific research has revealed previously hidden identities: that the temperature of a gas is the mean kinetic energy of its molecules; that light is electromagnetic radiation. In a similar way research in neuroscience is expected to show that the sound of a vacuum cleaner, a pang of hunger, the taste of mustard are nothing more or less than the firing of certain neurons.

The identity theory is not concerned to find neural correlations for mental states for brain states are everything that is meant by mental states. When I complain of a pain, then, whether or not I assent to this description, I am in fact referring to the condition of the piece of tissue inside my skull. It is not necessary to be able to pinpoint which part of the brain is involved in this pain or in any of my supposed mental states for the theory to make sense. The detailed mapping of the brain might prove a practical difficulty anyway since it is beyond the powers of neuroscience at 'the moment. The identification of which particular areas of the brain are involved at any particular time is an ongoing task for empirical science. The principle of the mind-brain theory, however, is quite clear: every thought, idea, desire, imagining, memory, sensation is nothing other than a particular electrochemical process in the brain. F-very reference to mental states, therefore, ought in principle to be capable of being paraphrased in the language of material objects and of natural forces.

The attraction of the mind-brain doctrine (or, for that matter, that of any monist ontology) lies in the fact that it avoids the apparent pitfalls of dualism. For dualism, in differentiating so acutely between two mutually exclusive entities, mind and brain, rendered interaction between them inconceivable; if mind and- brain share no properties, by what means, it is asked, do our physical states causally influence our mental states and vice versa? Clearly the advocate of mind-body identity avoids any such problem.


In Shakespeare's play, Twelfth Night, much of the comic confusion derives from mistaken identity. At various times Viola, disguised as a man, is believed to be her brother Sebastian and he is likewise taken to be her. This confusion persists as long as brother and sister are never seen on stage together. But as soon as they stand side be side confusion is at an end. One face, one force, one habit, and two persons is the comment of the onlooking Duke Orsino. There can now no longer be any doubt that the are not one but two and totally separate, Now the identity theorists take mind and brain to be one substance. I suggest that they are making a mistake because of a misunderstanding similar to that of the characters in Twelfth Night and that their mistake might be exposed in a similar way.

Suppose that 1, a convinced identity theorist, am given a brain scan. in an experiment the electrical activity of my brain is to be filmed and transmitted simultaneously on a television screen in front of me. I am, of course, to remain conscious throughout the experiment in which I am required to sip some tea, listen to some music, smell some perfume. As I carry out each activity, I watch the screen; I see areas of my brain light up, different areas for tasting, hearing, smelling. Now as an identity theorist I began the experiment convinced that sensations are nothing other than brain states Oust as for most of Twelfth Night characters see no difference between a woman dressed as a man and a man). But now as, for example, I sniff Chanel No 5, at the very moment when I enjoy its distinctively heady fragrance, I see highlighted on the screen a succession of parts of my brain: the olfactory bulb, the olfactory cortex, then parts of the thalamus and the hippocampus. Now that both mental and brain states are present before me there is no doubting the fact that they are two quite distinct entities. Just as Viola and Sebastian are indubitably not one man but brother and sister, so now I have learned empirically that mind and brain, matter and consciousness are not one but two separate entities.


Implicit in Response A is another rebuttal of the identity theory. I return to the imaginary experiment during which, together with the scientists and doctors who have set it UPI I am able to observe the scan of my brain. Also watching the proceedings on television screens around the world is an unlimited number of people. My brain is totally open to their public scrutiny; anyone can identify and measure precisely the parts of the brain which come into play during my experience of smelling the perfume; they can even count the number of neurons involved if they are so inclined. In theory, (though I might object, putting personal survival above the quest for scientific knowledge) the relevant brain cells could be extracted, then weighed, measured, examined under electron microscopes, despatched to any neurological laboratory in Japan or California, tested under strict clinical conditions. Everyone can have access to my brain parts which if not exactly public property are at least in the public domain.

But, in complete contrast, only I have access to the awareness of the perfume's smell. Its distinctive quality which cannot satisfactorily be expressed in words is felt in a private 'area' to which I alone have the key. Here is the crucial evidence which the identity doctrine cannot accommodate. For two entities to be identical, they must share all properties. The property of being public is possessed by one and the opposite property of being private by the other. Now if the identity doctrine were not implausible and unconvincing in an immediately obvious way then here is proof that it is irrational and spurious.

This is not the only point of significance that emerges from the imaginary experiment. Not only are the scientists and television viewers denied the direct experience that I have, but it is also impossible for them to deduce or even infer from the evidence of the brain scan (or from direct observation of the brain itself) the slightest clue about the nature of my private experience. Brain states and mental states have nothing remotely in common. There are no features about conglomerations of neurons that give the slightest inkling about particular mental states; it is impossible to infer from the closest imaginable study of firing neurons whether they are associated with the taste of cabbage, the hum of the motorway, the sight of a bird's nest or of any other sensations. (This is not to say that a scientist might not infer from the observation of the firing of the visual cortex, for example, that the person tested were having a visual experience. But this is a different case: the inference is drawn from the association of that part of the brain with the reports of earlier experiment volunteers. The scientist would not be drawing a conclusion directly from an observation of the brain.) Far from a relationship of identity between mind and brain, the two are totally and demonstrably alien to each other and yet, strangely, associated in some way as yet to be identified.


The next response is a more fundamental one and addresses presuppositions which underpin the doctrine. First a point about the language used in this area. The term, mind- brain identity, is ambiguous: it might mean

a) that brain is really mind, that there is no brain distinct from the mind or
b) that mind is really brain, that there is no mind distinct form the brain.

Either interpretation fits the notion of identity, the first a consequence of idealism, the second a consequence of materialism. In fact, what seems to be universally meant by mind- brain identity is the second. It is really the brain-only doctrine. The nature of the relationship of mind and brain is usually expressed in terms of how the language of mental events can be accommodated in a system of physical explanations. The reality of the physical which includes the brain is the unquestioned assumption of this approach.

The identity theorists take the existence of the brain as not problematic at all. It is their starting point. Descartes (not to mention Plato, Hume, Russell and other illustrious names) would have demurred at such presumption. And we might well ask, with them, whether the existence of the brain is indeed an indubitable first principle, a fundamental axiom beyond any question and whether the existence of mind, by contrast, is open to doubt, a category mistake, a mishap of language.

Suppose I ask, myself how I have acquired the knowledge that I have a brain. It occurs to me first that it might be possible to live my whole life without any such knowledge. Surely if I had grown up in a scientifically primitive age, I might have lived a full and rich life and never once have had any need for the concept of a brain? My tribe might have inculcated into me a belief that my skull contained a myriad of silent reptiles without any impediment to the quality of my life. In fact, the more I consider the matter the less I am convinced that I have knowledge of a brain. I cannot for certain base any knowledge of it on empirical evidence: 1, have never seen my brain and I have certainly never heard it, smelled it, tasted it or touched it. I have, for sure, seen pictures of a brain and seen and held models of it. In an unreflective way (and without too much concern for that old nuisance called the problem of induction) I might allow that if everyone else has a brain or to be more precise everyone whose skull has been opened — a very small proportion of the population, no doubt — has a brain, then it is likely that I have one too.

There are plenty of ifs and assumptions so far but let them all be granted. I concede that if my head were split open a brain would be revealed. Revealed, yes, but revealed to what? Would the brain be a raw, brute fact? Or would it be in a sense secondary, an interpretation from evidence rather than the actual evidence itself. Surely this revealed brain is a feature of a visual sensation, an appearance within a mental event? Certainly it is not an entity to which I have direct access. It is not itself a first principle but an inference from or mediated through a first principle, consciousness. Furthermore, what is true of the sense-datum of seeing my brain is true of seeing or sensing any material object, namely that the material object appears to us as the content of the sense-datum. Here is the crux of my third objection to the materialists who propound the doctrine of mind-brain identity, that they make a fundamental mistake at the beginning of their investigation. They take the material as their Archimedian point and so build a philosophy of consciousness on a dangerously fragile basis. They try to explain what is thoroughly grounded and certain in terms of what is assumed, and subject to doubt. It is surely closer to reality to commence with mental events as foundational and to worry next whether they coexist with a physical world for it is within mental events that material bodies make their appearance.