Non-reductive physicalists hold that mental properties are realized by physical properties. The realization relation is typically taken to be a metaphysical necessitation relation. Here, I explore how the metaphysical necessitation feature of realization can be explained by what is known as "the subset view" of realization. The subset view holds that the causal powers that are associated with a realized property are a proper subset of the causal powers that are associated with the realizer property. I argue that the said explanation of the metaphysical necessitation feature requires a careful treatment of the relationship between properties and causal powers.
***Non-reductive physicalism is typically understood as the view that mental properties are realized by physical properties. What counts as a case of realization is widely disputed.1 According to a commonly-held view, realization is a relation between two properties, the realizer property P and the realized property Q, whereby something's having P somehow brings about its having Q. Surely, "brings about the instantiation of" is a predicate that can pick out many relations. What is distinctive about realization, according to the standard picture, is that such bringing-about is supposed to hold non-contingently and synchronically: If P realizes Q, then, as a matter of metaphysical necessity, if x is a bearer of P at a time t, then x is also a bearer of Q at t.On this understanding, if physicalism is true, insofar as x is a bearer of a physical realizer of a mental property M, there isn't anything that needs to be added to the intrinsic properties of x to make it the case that x has M. Thanks to taking realization as a metaphysical necessitation relation, we can easily distinguish a realization-based version of non-reductive physicalism from some non-physicalist views which also hold that mental property instances are brought about by physical property instances where such bringing-about holds only contingently.2 It 1 See Baysan (2015) for discussion of different accounts of realization.2 Noordhof (2003) persuasively argues for a related claim. As an example of such non-physicalist views, consider the view that phenomenal mental properties supervene nomologically, but not metaphysically, on physical properties (Chalmers 1996).