In this article we explore the positive use of "social identity" in order to explain certain instances of social action. We attempt to isolate its explanatory power alongside the two great motivational mechanisms of the sociological tradition: interests and instrumental rationality, on the one hand; and values, norms and practical reason, on the other. We discover an ample sphere for a reductionist strategy where identity is and must be translated to the language of either interests and preferences or norms and values with which the individual identifies himself. Nevertheless, in the final part of this paper we also explore the possibility and circumstances of the appearance of reasons of identity proper as independent and irreducible agency factors.