 Mumford (1998, chapter 7) endorses this argument when it is construed as an argument against the ‘type-type’ identification of dispositions with their bases that Armstrong defends. But Mumford takes a strategy familiar from the philosophy of mind and maintains that Prior et al.’s argument does not defeat his own ‘token-token’ identification. According to Mumford, although in general dispositions are not identical with their bases, each instance of a disposition is identical with an instance of its causal basis. Anticipating Mumford’s response, Prior (1985) complains that it is not at all clear what can be meant by ‘property instance’ if, as Mumford maintains, an object’s instance of property \(A\) can be the very same thing as its instance of property \(B\), even though property \(A\) is not the same as property \(B\). Even if we grant the intelligibility of such a notion of property instance, however, might not the very same argument from rigid designation show that instances of dispositions cannot be identical with instances of their bases, any more than dispositions themselves can be identical with their bases? Such would seem to be the appropriate lesson to draw from the fact that Kripke’s original version of the argument, aimed against identity theories in philosophy of mind, applies as much to token-token as to type-type versions of the identity theory. Mumford disagrees (p. 157), although he says little to substantiate his disagreement. (See Rives 2005 for another objection to Mumford.)