 Functionalism about properties of a given sort is the view that such properties are functional in nature. For example: Functionalism about the mental is the view that mental properties are functional. Intuitively, a functional property is a property whose nature, essence or significance is fully captured by a description of the role it plays within a system. Versions of functionalism can be distinguished with respect to the sort of role they attribute to functional properties and the sorts of resources required to specify those roles. The relevant roles might be specified solely in terms of causal input-output relations. Alternatively, they can be conceived of in terms of relationally defined computational states (computational functionalism), or in terms of goal-directed interactions (teleological functionalism) (cf. Block forthcoming; Lycan 1987; Van Gulick 1980; Sober 1990).