Forthcoming In Byrne and Thomson (eds.) Content and Modality: Themes from the Philosophy of Robert Stalnaker

2. The first of our trio, physicalism, is the thesis that, not necessarily but as a matter of fact, everything is physical. This thesis stands in need of clarification. For one thing, we need to be told what it is to be physical. This is a difficult and somewhat neglected question, but I want to set it aside. A rough and ready understanding will do for present purposes. Another aspect of the thesis requiring clarification is the sense in which it pertains to everything. There are a number of proposals about how to explain this, but here it is sufficient to identify physicalism as the thesis that the physical truths entail (in the sense of necessitate) all the truths, and so all the psychological truths. If this is physicalism, and if it is true, then it is contingent, i.e. true not necessarily but as a matter of fact. For it is contingent which truths are the physical and psychological truths at any given world. If the physical truths concern only extension in space and time, and the psychological truths concern ectoplasm, the physical truths will not entail the psychological. On the other hand, if the physical truths are as multifarious and complex as those that (we assume) obtain in our world, and if the psychological truths concern experiences more or less as they are construed by folk psychology, physicalism might be true. Physicalism is if true contingent, but there is nevertheless a necessary truth lurking in the shadows that is important for our purposes to bring out. For suppose that