Brewer, M.B., (1991) The social self – On being the same and different at the same time. Personality and Social Psychology Bulletin. 17(5): 475-482.
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Brewer's Distinctiveness Theory argues that the composition of an individual's social identity necessitates a trade-off between the needs for assimilation and the need for differentiation. This is in contrast to previous models of social identity who assumed that individuals aim at maintaining some balanced level of similarity with other people on a unidimensional similarity/dissimilarity scale.
The key implications of the theory lay in its dynamic aspects, as it is argued that individuals continuously take corrective actions to maintain an optimal compromise between the two needs. For instance, a person feeling too unique might achieve more assimilation by joining a group and making comparisons with ingroup members (and finding similarities). Alternatively, a member of a large overly inclusive group might try achieve distinctiveness by making inter-group comparisons. Such actions are undertaken until the individual reaches an equilibrium, that is when his/her needs for assimilation and differentiation are equally activated.
As pointed out by Brewer (1999) in later work, this has implications for the study of prejudice and intergroup processes as one can ask if "ingroup preference and loyalty can exist without spawning outgroup fear or hostility" (p. 434).
Brewer, M.B. 1999. Psychology of Prejudice: Ingroup Love or Outgroup hate? Journal of Social Issues, 55, 429-444.
Hogg, M.A., Terry, D.J. & White, K.M. 1995. A tale of two theories: A Critical comparison of identity theory with social identity theory. Social Psychology Quarterly, 58, 255-269.