Abstract
The majority of contemporary philosophers of mind are physicalists. The majority of physicalists, however, are non-reductive physicalists. As nonreductive physicalists, these philosophers hold that a system's mental properties are different from a system's physical properties, that is, they hold that the sum total of mental facts about some system is a different set of facts than the sum total of physical facts about the same system. As physicalists, however, these nonreductivists hold that mental facts are nonetheless determined by physical facts, that is, they subscribe to the supervenience thesis, i.e., the thesis that no mental differences can obtain without physical differences obtaining. In this paper I take up the issue of how best to understand the notion of supervenience, especially in the light of recent advances in the neurosciences