Social identity poses one of the most important challenges to rational choice theory, but rational
choice theorists do not hold a common position regarding identity. On the one hand, externalist
rational choice ignores the concept of identity or reduces it to revealed preferences. On the other
hand, internalist rational choice considers identity as a key concept in explaining social action,
because it permits expressive motivations to be included in the models. However, internalist
theorists tend to reduce identity to desire -the desire of a person to express her social being. From an
internalist point of view, that is, from a viewpoint in which not only desires but also beliefs play a
key role in social explanations as mental entities, this paper rejects externalist reductionism and
proposes a redefinition of social identity as a net of beliefs about oneself, beliefs that are indexical,
robust and socially shaped.the First ISA Forum of Sociology. Barcelona, Spain.September 5-8, 200