This paper deals with a genuinely sociological issue in the light of feminist epistemology: it studies the category of "woman" as a means of classifying people according to gender. Discussing the gender theories advanced by C. Delphy and I. M. Young, it first emphasizes, with J. Widmer, that gender is actually incapable of determining social relations. Based on H. Sacks's studies, it also shows how important it is to (a) distinguish between woman as an "empirical individual" and woman as a "class of people" and (b) take into account the ordinary practices of categorization. These two principles are the necessary conditions for developing a complete and strong sociology that treats sex categories as topics of inquiry rather than as resources for conducting it. Afterwards, the paper discusses J. Butler's poststructuralist philosophy of gender. This theory, with the notion of performance, offers an adequate approach to gender identities inasmuch as they are conceived as phenomena emerging from action. Confronted with H. Garfinkel's ethnomethodology of gender, it would appear, however, that Butler's performance thesis does not allow one to take into account sex categories that are in use due to a poor conception of the scripted nature  of the social world. On the other hand, the accomplishment thesis of gender supported by H. Garfinkel is unable to conceive of "doing again" in any other way than "doing the same." Through an analysis of a few everyday life situations, the paper finally seeks to implement a praxeological sociology of sex categories that escapes this twofold aporia.