James Cornman was a defender of non-reductive materialism when it came to the issue of mind-brain interaction. In other words his analysis of what the ‘mind’ was, was in the end that it was identical with the brain (i.e., material). However, he proposes that this commitment to the mind being identical with the brain does not commit him to making the concession of the reductive materialist, who also admits that the mind is nothing but the brain. In an article of his titled A Nonreductive Identity Thesis about Mind and Body, he writes the following:
What is required for A to be identical with B[?] Following what is known as Leibniz’s Principle of the Identity of Indiscernibles, we can say, somewhat roughly, that A is identical with B if A and B have exactly the same properties; and A is not identical with B if one of them has a property the other one lacks… If A is nothing but B, then A is identical with B. But the converse is false. A can be identical with B, yet not be nothing but B. Identity is a symmetrical relationship. Thus, if A is identical with B, then B is identical with A. But it is false that if A is nothing but B, then B is nothing but A. The latter relationship is nonsymmetrical. Consequently mere identity is not sufficient for the reduction that “nothing but” implies… Consider the following sentences:
- The object that frightened you in the cemetery last night is identical with the gnarled tree behind Jones’ grave.
- The gnarled tree behind Jones’ grave is identical with the object that frightened you in the cemetery last night.
- The object that frightened you last night is nothing but the gnarled tree behind Jones’ grave.
- The gnarled tree behind Jones’ grave is nothing but the object that frightened you last night.
Obviously Cornman’s intention is that we recognize the fourth sentence to be obviously false. Something about this seems rather fishy to me. First, the example is not a great one in part because it is not clear that it is comparing two predicate-bearing substances. Plausibly we can say that there just is no object that frightened us in the cemetery last night, but rather that the event of our being afraid was caused in part by some object. I’m not a fan of the old school empiricist distinction between primary and secondary qualities, but it seems that if anything is a secondary property it would be the predicate ‘frightens people’. Moreover, suppose that by the terms ‘gnarled tree behind Jones’ grave’ and ‘object which frightened you’ we were to think that the same substance was being picked out; then clearly the fourth sentence is true given the Identity of Indiscernibles. Cornman’s suggestion to show us the way towards a nonreductive identity thesis, is smoke and mirrors. It doesn’t help us because his example is a poorly conceived one, and if one rewrites the same sentences by replacing ‘gnarled tree behind Jones’ grave’ with ‘mind’ and replacing ‘object which frightened you’ with ‘brain’, the problem impresses itself clearly on our minds once again.
The mind and the brain are not terms which pick out the same thing such that the mind has all and only those predicates which the brain has, and the brain has all and only those predicates which the mind has. That whole conjunction is simply not true, even on Cornman’s account. Moreover we can press against Cornman that it remains completely unintelligible to say that the mind is identical with the brain (in the materialist’s sense – I am assuming that Cornman is not a Leibnizian phenomenalist with respect to matter), and yet that it is ‘more than’ the brain. If some theory cannot be understood then how can it be accepted?
There may be instances in which some Christians want to speak about two things being identical without being ‘nothing but’. For example, my body, according to Christianity, is identical with me, and thus I am identical with my body, but I am not ‘nothing but’ my body. First we should say that the identity-relation involved here is not necessarily as strong as Leibniz’ identity-relation according to his Principle of the Identity of Indiscernibles. Second, ‘my body’ merely pick’s out the extension of a substance, or else it picks out the substance. If it merely does the former, then the identity relationship is like the relationship of ‘belonging to’ something or other (the extension belongs to the substance, the body belongs to the soul, etc). If it does the latter, then again the identity would be strong enough for Leibniz’ stringent principle.