  Naturalism in metaphysics has been on the ascendancy for some time, though it is often somewhat difficult to ascertain exactly what the position amounts to. Metaphysical naturalists claim that there are only natural properties, in some good sense of the term ‘natural’. Usually naturalism is taken to rule out at least the existence of supernatural entities or properties. And one standard way that naturalists have defended their position has been to reduce seemingly mysterious properties or objects which might appear to be non-natural to more familiar purportedly natural properties. That is, they have tried to show that these objects or entities are nothing over and above some set of natural properties or objects appropriately arranged. One strategy is to identify seemingly suspect properties with natural properties, either via connecting definitions or through synthetic identities. In this way the seemingly suspect properties can be allowed into the naturalist’s ontology without undermining the commitment to naturalism. Many naturalists have taken this approach to moral properties (Firth 1952; Railton 1986; Boyd 1988).