Constitution is Identity

In his interesting article Constitution is not Identity (1992) Mark Johnston argues that (in a sense soon to be explained) constitution is distinct from identity. In what follows I dispute Johnston's contention. In this section I explain what is at issue and the main positive argument Johnston gives for his position. In ? II I suggest that an argument for the thesis that constitution is identity (hereafter thesis (CII)) which Johnston describes as especially worthy of respect, is, in fact, even more worthy of respect than he thinks, since his criticisms of it fail. In ? III I emphasize a (surprisingly neglected) argument of David Lewis's for a four-dimensional metaphysic and attempt to bring home the implausibility of maintaining the distinctness of constitution and identity within the context of such a metaphysic (in this section I draw on, and put to my own use, a recent discussion by Peter Simons (1991)). Finally I suggest, in ? IV, that the vagueness of de re modal statements cannot be accommodated satisfactorily within Johnston's position (in this section I am heavily indebted to Christopher Hughes (1986) and Ernest Sosa (1987)). Johnston begins with Gibbard's well-known example (1975) of 'Goliath and Lumpl. Goliath is a statue and Lumpl is the piece of clay from which it is made. Goliath and Lumpl coincide at all times at which either exists. Unless we are prepared to accept that purely material entities of identical material constitution at all times may nonetheless be distinct, we must accept that Goliath and Lumpl are identical. Yet there are modal predicates true of Lumpl which are false of Goliath, and modal predicates true of Goliath which are false of Lumpl. For example, Lumpl might have been squeezed into a ball and not destroyed, which is not true of Goliath. On the other hand, Goliath might have had its arms and calves replaced by new parts and continued to exist, which is not true of Lumpl. Similar examples occur frequently in the literature and they present philosophers with an uncomfortable choice. Thesis (CII), i.e. the thesis that purely material entities of identical material constitution at all times cannot be distinct merely in virtue of differences in modal, dispositional or counterfactual properties, is a very plausible one, but in cases such as that of Goliath and Lumpl it seems to be in conflict with Leibniz's Law. Hence we must either reject (CII) or