 A function may figure into the ontology of a social kind K in any of several ways. The simplest is for K to be defined by a causal role R that its instances perform. In that case, K is a “causal role kind”. Take, for instance, the role serving to minimize the role of family in selecting a mate. Alternatively, certain social categories may better be understood as realizers of functional roles. A realizer-kind is often defined in terms of process or physical characteristics, where things that have those characteristics normally perform a role (see Block 1980, McLaughlin 2006).