Introduction

In this essay my primary focus will be on the why of supervenience, rather than the what. That is, I shall be more concerned with the arguments for supervenience, in particular for the supervenience of the mental on the physical, than with questions of precisely how to formulate the doctrine. Much has been written on the latter topic, but relatively little on the former. I think this is a pity, for it has encouraged the view that the supervenience of the mental on the physical depends on some kind of basic intuition and that those who find physicalism unappealing are therefore free to reject it. I will show that, on the contrary, the doctrine of supervenience is a simple consequence of some evident truths. (Of course, the “why” of supervenience is not entirely irrelevant to the “what”: once we understand the argument for the doctrine, we will be better able to see which versions of it are defensible.)

Once I have laid out the argument for supervenience, it will be helpful to compare it with a related argument for the thesis of physical realization (i.e., in the mind–brain case, the thesis that mental states are always realized by physical states). The relationship between the doctrine of supervenience and the doctrine of physical realization is not always well understood. Distinguishing the reasons for believing these two doctrines will help to clarify their relationship.