The category women is a central analytic category of feminism, but has been very troubled in feminist theory and philosophy. In the background of the troubles with the category women is the metaphoric image of a social category as a set and its exemplars as set members. But the category women cannot be defined as sets are defined, so that is an inappropriate metaphor. A number of feminists and race theorists turn to Wittgenstein, who offers alternative metaphors. This chapter explores the powers and resonances of his metaphors—in the case of "family resemblance," using the work of cognitive psychologists Rosch and Mervis on categories that have prototype structure.