There are two problems concerning the implications of certain forms of supervenience that I wish to discuss. The problems are connected in that their resolution depends on deciding what sort of enterprise we are engaged in when we approach the problems. Supervenience can be formulated and discussed as a purely logical set of formulas, which are indeed quite engaging in their own right. On the other hand, much of the interest in supervenience has been generated by its apparent usefulness in understanding certain philosophically perplexing realms of life, for example, mentality and morality. These two conceptions of supervenience can come into conflict with one another, as we will see. The conflicts provide the opportunity to assess our motivations.

The First Problem

Suppose we accept supervenience in the form of the Quinean slogan “No difference without a physical difference,” or, as Davidson puts it for one particular case, “There cannot be two events alike in all physical respects but differing in some mental respects.” Does it follow from this that there are principles, that is, universal generalizations, in which sufficient conditions are given in physical (or subvening) terms for the presence of certain supervening qualities?

It might seem as though there obviously are such principles. Consider some mental state that I am now in, say one of anxiety. By our assumption, no one can be nonanxious without also differing from me in some physical way.