 We have been assuming that supervenience physicalism is distinct from type physicalism. But it is worth noting that, there are ways to understand supervenience according to which this difference is less obvious. The reason for this has to do with questions concerning the logical (or Boolean) closure of the set of physical properties — if P, Q and R are physical properties, which of the various logical permutations of P, Q and R are likewise physical properties? On some assumptions concerning closure and supervenience, supervenience physicalism (construed as a necessary truth) entails type physicalism; on other assumptions, it doesn’t. But the problem is that the assumptions themselves are difficult to interpret and evaluate, and so the issue remains a difficult one. It is not necessary for our purposes to settle the question concerning closure here. (For further discussion of these issues see Kim 1993, Bacon 1990, Van Cleve 1990, Stalnaker 1996.)