Contemporary physicalists typically reject two opposing positions concerning the relation between physical and psychological properties: Cartesian dualism and reductive physicalism. In doing so, they embrace some kind of nonreductive physicalism entailing that psychological properties depend on, but are irreducible to, physical properties. This essay assesses the viability of such nonreductive physicalism. In particular, it examines whether nonreductive physicalism can, with help from certain nonreductive supervenience relations, steer a clear course between Cartesian dualism and reductive physicalism. We shall see that the course is far from clear, owing to complications facing a physicalist account of the pertinent notion of dependence. Physicalist psychofunctionalism in particular, we shall contend, raises serious problems for current conceptions of nonreductive mind-body supervenience relations, owing to its requiring relatively local causal mechanisms for the occurrence of psychological properties. Let us begin with sketches of the two positions nonreductive physicalists aim to avoid: dualism and reductionism.

Dualism and Independence

Cartesian dualism affirms the ontological independence of the psychological from the physical, in a sense to be specified. Cartesian substance dualism implies that psychological substances (e.g., thinking individuals) do not depend ontologically on physical substances or properties. Cartesian property dualism implies that psychological properties – psychological features that can be exemplified by individuals – do not depend ontologically on physical substances or properties. Cartesians, following Aristotle, might distinguish substances and properties roughly as follows: properties are predicable of things and are multiply realizable, but substances are individuals that are not thus predicable or realizable.