Abstract

Jackson says that the form of physicalism that I recommend, with certain emendations he believes are necessary, turns out to be none other than the “Australian” type-type identity theory of J.J.C. Smart and others. About this, too, I have no serious disagreement, although Jackson’s claim appears to depend, at least in part, on a certain chosen reading of the texts involved. In fact, one point of similarity may be worth noting. As I take it, one special feature of the “Australian” type identity theory is the claim that mental-physical identities are contingent, not necessary. Suppose M has a single physical realizer, P. On my account, the statement that M = P is not metaphysically or logically necessary. It is contingent since the statement that P realizes M is contingent. This is so because for P to realize M is for it to fulfill the causal specification that defines M, and what causal relations P actually enters into is a question that depends on the laws prevailing in a given world. Thus, P may be a realizer of M in this world but perhaps not in another in which different laws hold; in some worlds M may have no realizers at all. None of this is in violation of the idea that identities are necessary. For, according to me, if M has realizers, M is a functional property defined by a causal specification. This means that “M” is not a rigid designator, though it is, as we might call it, “nomologically rigid” or “semi-rigid”.