At the end of Chapter 4 we started to move away from issues in naturalized epistemology and began to ask questions about ontology. We entertained questions concerning the existence of unobservable entities, numbers and possible worlds, among other things. In this chapter and Chapter 6 we ask: is there such a thing as naturalized metaphysics? Is there a description of how the world is in very general terms that should be endorsed by a naturalist?

Physicalism as naturalism

For many naturalists the answer to this question is straightforward. Naturalism is synonymous with another “–ism” – physicalism. Physicalism is the naturalistic successor to the materialism of Democritus and Hobbes. Physicalists have learned from science that there is more to the world than the atoms and the void. There are fields and forces and superpositions of state too. Good naturalists as they are, physicalists let scientists fill in the details concerning exactly what there is. Once the scientists have figured out what the fundamental physical constituents of the world are, then the content of physicalism can be stated very simply. According to physicalists, everything is or is in some appropriate way dependent upon the physical. (We'll worry later about what “in some appropriate way dependent upon the physical” might mean.)

We need to ask two questions. The first concerns the justification of physicalism. What is it about the claims of physicalism that demand assent? The answer for a naturalist must be that our best science supports this metaphysical view.