The semantic basis and morphosyntactic reflexes of Kiowa-Tanoan noun classification are perspicuously captured in a system with three bivalent number features: [±singular], [±augmented], [±group]. Privative analyses of the same facts require, inter alia, features without semantic motivation, syntactic mechanisms that violate Inclusivity, and feature annotation reminiscent of bivalence. The semantic atoms of number are, therefore, bivalent.