 A functionalist about the mind might offer (5) as a part of a more comprehensive metaphysical explanation of the nature of pain and its instances. And yet, (5) invokes causation in at least two places. For one thing, the explanans of (5)—i.e., the fact which does the explaining—invokes a type of causal process. In addition, the explanandum of a metaphysical explanation—i.e., the fact to be explained—can invoke causation, as for instance would be the case were one to offer up a metaphysical explanation of causation itself. Thus what makes a metaphysical explanation non-causal is not that the explanans or explanandum are themselves non-causal, but rather that the relationship between them is. For another thing, (5) works at least in part due to the relationship between the functional role of a mental state and its realizer. So if this relationship itself consists in some relationship between the causal powers of a mental state and its realizer (perhaps the former must be a proper subset of the latter; see J. Wilson 1999, Shoemaker 2001), then to that extent, (5) derives its explanatory power from causal facts. But (5) does not derive it solely from these, for presumably the relationship between the causal powers of a mental state and its realizer is not itself a causal one (in the case of Wilson and Shoemaker, it is the is a proper subset of relation).