 Realization is primarily taken to be a relationship between properties, though derivative notions of property instance realization and state of affairs realization have been defined. We will focus on property realization. There is more than one use of the term ‘property realization’ in literature. Perhaps the leading use is the one found in the literature on the functionalist theory of mind. (See, e.g., Block 1980; Melnyk 2003, 2006). On the functional view of realization, one property F realizes another G just in case F occupies (or fills or plays) the causal role associated with G, ‘the G-role’—that is, just in case instances of F have the kinds of causes and kinds of effects that comprise the G-role. Thus, for instance, a neural property will realize pain just in case it has the kinds of causes and effects that comprise the pain-role. (According to analytical functionalism, the pain-role is the causal role that folk psychology associates with pain; according to psychofunctionalism, it is the causal role that scientific psychology associates with pain.) If more than one property plays the G-role, then G is multiply realizable. (See the entry on   multiple realizability.)  