According to Jeffrey Poland, the “basic conviction” of the physicalist is that:
… phenomena occur in nature in virtue of what goes on in the physical domain … My approach will be to frame theses that express the following idea: given that all individual phenomena, all regularities, and all instances of and exceptions to regularities which occur in nature occur in virtue of physical phenomena, there are physically-based explanations of all such phenomena. (Poland , pp. 207–8)
I agree with Poland that this sort of explanatory claim is central to the physicalist idea. In this chapter I explore how we may fill out and clarify that explanatory claim in terms of its modal implications. In particular, I focus on two sufficiency claims to which physicalism is committed. Ultimately, there is no way to replace the explanatory claim with sufficiency claims; nonetheless, there are good reasons to focus on them. They help cash out the demands of physicalism, giving us a better grasp on its content. In so doing, they also put us in a better position to evaluate apparent counterexamples to physicalism, think further about the implications of physicalism for science, and, perhaps most urgently, get clear on what sense there is to be made of so-called naturalization projects. Further, they provide a dialectically useful route to justifying physicalism itself. As I shall argue at the end of this chapter, if they are true, it is overwhelmingly likely that the overarching explanatory claim is true.
Physicalistic Explanation and Sufficiency
In what sense is the physical realm supposed to explain everything else?