Abstract

Contemporary materialism labors under two serious difficulties: the problem of formulation and the problem of justification. It remains unclear just what physicalism says or why one should believe it. I propose an explicit formulation and provide a sustained argument for that specific thesis. The overall thesis I defend may be roughly stated thus: every nonphysical particular and lawful fact in the actual world is to be explained by reference to the purely physical in such a way as to imply that they are nothing over and above the physical facts, where the purely physical facts include the particular physical facts, the laws of physics, and the completeness of physics. This explanatory claim implies two dialectically key theses which may be roughly expressed as the following. First, any possible world physically indiscernible from the actual one which abides by the laws of physics is indiscernible from the actual one in all respects. Second, any actual law of nature is entailed by the laws of physics, their completeness, and actual particular matters of physical fact. This is a very strict sort of physicalism, one that probably deserves the name "reductionism." ;The core argument turns on the notion of a physically detectable property, that is, a property such that whether it is instantiated can make a difference to physical effects, where this "making a difference" is a causal notion. Given the completeness of physics--the claim, roughly, that every physical event has a sufficient physical cause--all physically detectable properties are plausibly derivative on purely physical properties and laws in such a way as to imply the physicalist thesis described above. I argue that being physically detectable in the relevant way is linked to empirical knowability so that any property instance we could be justified in positing is physically detectable and hence swept up in these considerations. The detectability considerations allied with the completeness of physics provides both the supervenience thesis about particular facts and the law entailment thesis. Together, these make the overarching explanatory claim--that the nonphysical realm is nothing over and above the physical--extremely plausible