1. Is it logically possible that some or all 'mental' events are identical with physical events occuring in someones brain, or that mental states are identical with physical brain states? This is the core of the 'mind-brain identity' controversy.
2. I would first like to consider a number of hypotheses, none of them obviously self contradictory or incompatible with its fellows, which together would constitute those conditions under which we should feel most strongly the plausibility of such an identification. This will perhaps help us to see whether the mind-brain identity theorem is coherent. The advocates of the mind-brain identity theorem have held the identity to be a case of contingent identity, which would be true if some sort of materialist doctrine were true. The hypotheses below amount to a very strong doctrine of materialist-determinism, they are probably every one of them false.
3. Materialism is an ontology. It asserts that fundamentally only matter exists (perhaps more plausibly mass/energy, I shall count a mass energy ontology as materialist). Every ontology goes hand in hand with a theory of meaning. In so far as a statement has factual or descriptive content it must be by referring to things which do or can exist, so for the materialist a statement which cannot be understood as saying something about matter must have no factual content. If there is some language which is capable of expressing all propositions about matter, then this language has a special status in a materialist scheme; any statement in any language whatever either has no factual content, or is equivalent in factual content to some statement in this special language. This amounts to a sort of translatability, not one preserving meaning, but preserving rather, descriptive content.
4. The first two hypotheses in our strong materialist position are:
| 1. | Only matter (or perhaps mass/energy) exists. |
| 2. | There is a language (materialist language) which can be used only to make statements about matter, and which is capable of expressing any coherent proposition about matter. |
5. Now if we define 'factual content' of a proposition as what it says about matter then every statement which has any factual content is equivalent in factual content to some statement in materialist language. If hypothesis 1 is true then surely this definition of factual content is sensible, for nothing sensible can be said of what does not and cannot exist. If we apply this to statements about mental states or events we have to conclude that every such statement is equivalent in factual content to some statement in materialist language. From here it is, at least superficially, a small step to some sort of mind/brain identity position, for surely, if to say in the language appropriate to mental happenings something of the form 'p occurred' is equivalent in factual content to some statement in materialist language of the form 'q occurred', where 'p' would be some mental event and 'q' some physical event (or rather, material), then in some sense p and q must be the same event.
6. Having outlined somewhat crudely a route to some mind/brain identity theory I shall now look back at some of the holes in the argument to see what additional hypotheses are necessary to tie it together. The identification of the mental and the physical is provoked primarily by the conflict between the materialist ontology, and the belief that statements about mental events are significant and have genuine descriptive content. The identification is only necessary if we are not prepared to discard either one of these two beliefs. What is required then to strengthen the scheme is further support for these beliefs.
7. In order to make the materialist ontology, and hence its associated theory of meaning (or rather, 'descriptive content') more credible I propose the following hypotheses:
| 3. | Every conscious experience is correlated with a certain material state of affairs. |
| 4. | Time is distinct from space in such a way as to make it sensible to speak of 'the state of the universe at time t1' (this contradicts the theory of relativity due to Einstein but would nevertheless seem to be logically possible. |
| 5. | The number of states of the universe is denumerable (the number of possible states, that is) if we confine ourselves to the material aspects of such states only. |
| 6. | Given the state of the universe at time t there is an effective procedure for computing the state of the universe at any subsequent time. |
| 7. | The correlation asserted to exist in hypothesis 3 is such that distinct conscious experiences are always correlated with distinct material happenings. |
8. Hypotheses 4,5, and 6 give us together the materialist-deterministic scheme I spoke of. I include 4 because to formulate a deterministic scheme in a universe where simultaneity is not a coherent relationship between events poses problems which I would rather sidestep for present purposes. The denumerability of states of the universe is a necessary condition of these states being finitely representable, which in turn is a necessary condition of there being an effective procedure for computing the state of the universe at some time given the state at some preceding time. The correlations referred to in hypotheses 3 and 7 are correlations between events or states of affairs, not correlations between statements about such things.
9. The purpose of these hypotheses is to render, as strongly as possible, all things explicable in terms of the materialist scheme. Two things which might cast doubt upon the materialist ontology, and which these hypotheses were intended to exclude were:
| a) | The possibility that those things of which we are directly aware do not fit into the materialist scheme. This would be the case if two distinct mental states were found to be correlated with the same material state. Clearly if we can distinguish between states of affairs which the materialist sees as identical then there must be something other than matter to account for the distinction. |
| b) | The possibility that by supposing immaterial entities to exist we can give a more satisfactory account of the relationships between our experiences. Even if the present material state of the universe is sufficient to establish precisely the mental state of every individual in that universe, it does not follow that it is enough to establish future material states of the universe, and hence future mental states of individuals. It may therefore fail to represent a completely satisfactory account of our experience. If the state of the universe (material part) at time t1 were identical with that at some other time t2, and yet the state one second after t1 differed from that one second after t2, then we would have reason to doubt that knowing the material state of the universe we know all that there is to be known (about the state at a given time). So long as the materialist account remained inadequate in such a way there would be the possibility that a more complete account of the way our experiences follow one on the next could be obtained by supposing that other things than the material exist. By introducing immaterial things we might be able to distinguish states of the universe which were materially indistinguishable, and hence account for the differing subsequent states of the universe. Now from the hypotheses I have put forward it follows logically that if the material state of the universe at t1 is identical with that at t2 the the state at any given time after t1 is identical with that the same amount of time after t2. It is therefore difficult to see how invoking the immaterial could better explain out experiences and the way in which they succeed one another. |
10. (I must concede here that hypothesis no.6 is not explicit enough on this matter. It would be better reading:
| 6. | There is an effective procedure for computing the state of the universe at time t plus n seconds given only the state at time t, and the value of n. (not given the value of t) |
11. The deterministic universe which I have outlined so far is not a causal universe, or at least not necessarily one. A completely causally determinate universe need not necessarily satisfy any of the hypotheses I have so far put forward (though it might satisfy all of them), but it must satisfy certain other conditions. The additional conditions for causal determinism arise from the need for spatio-temporal contiguity of cause and effect. To support the mind/brain identity thesis a causally deterministic scheme is not necessary as far as I can see, and so I shall not attempt to formulate more precisely the conditions necessary for a deterministic model to be causal. Some additional hypotheses concerning location are necessary however in order to enhance the identification of mind and matter into an identification of mond and brain.
12. It is worth noting just how loose the framework which I have put forward is. In presenting the deterministic aspects of the framework I made no reference to location whatever, except to say that the space and time are to be quite distinct. The only requirement was that knowing the state of the entire universe at some time is enough to enable us to establish the entire state of the universe at a subsequent time. This does not entail, for example, that knowing the state of any small region of the universe enables us to make any prediction whatever.
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written early 1975, edited into HTML 1997/4/23 last modified 1998/04/01