A social identity is the portion of an individual’s self-concept derived from perceived membership in a relevant social group. As originally formulated by Henri Tajfel and John Turner in the 1970s and the 1980s, social identity theory introduced the concept of a social identity as a way in which to explain intergroup behaviour.
Social identity theory is best described as a theory that predicts certain intergroup behaviours on the basis of perceived group status differences, the perceived legitimacy and stability of those status differences, and the perceived ability to move from one group to another. This contrasts with occasions where the term “social identity theory” is used to refer to general theorizing about human social selves. Moreover, and although some researchers have treated it as such, social identity theory was never intended to be a general theory of social categorization. It was awareness of the limited scope of social identity theory that led John Turner and colleagues to develop a cousin theory in the form of self-categorization theory, which built on the insights of social identity theory to produce a more general account of self and group processes. The term social identity approach, or social identity perspective, is suggested for describing the joint contributions of both social identity theory and self-categorization theory.
Social identity theory has been criticised for having far greater explanatory power than predictive power. That is, while the relationship between independent variables and the resulting intergroup behaviour may be consistent with the theory in retrospect, that particular outcome is often not that which was predicted at the outset. A rebuttal to this charge is that the theory was never advertised as the definitive answer to understanding intergroup relationships. Instead it is stated that social identity theory must go hand in hand with sufficient understanding of the specific social context under consideration. The latter argument is consistent with the explicit importance that the authors of social identity theory placed on the role of “objective” factors, stating that in any particular situation “the effects of [social identity theory] variables are powerfully determined by the previous social, economic, and political processes”.