 Opposing the identity of dispositions with their causal bases, Prior et al. present arguments for what they call the ‘Distinctness Thesis’. One of them is the argument from rigid designation, which we have just discussed. Another springs from the possibility of multiple realization of dispositions. Different fragile objects, for example, have different causal bases—some are fragile in virtue of their irregular atomic structure, some are fragile in virtue of their weak intermolecular bonding. This seems to serve as evidence for the Distinctness Thesis. Why? If dispositions were identified with their causal bases, we will end up having to say that diverse causal bases of fragility are identical to each other. But they are, ex hypothesi, distinct from each other. And so Prior et al. argue that the multiple realizability of dispositions provides a reductio basis for the Distinctness Thesis.