 Views about the relation between dispositions and their causal bases mirror views about the relation between mental and physical properties. Armstrong, Martin &amp; Place (1996) and Mackie (1973, 1977) defend a ‘type-identity theory’ according to which any disposition is identical with its causal basis. Mumford (1998) defends a ‘token-identity theory’ according to which any instance of a disposition is identical with an instance of its causal basis. Prior—together with Pargetter and Jackson—defends a ‘functionalist theory’ according to which a disposition is a second-order property of having some causal basis or other. There are other views too, but we will confine discussion here to the three mentioned above.