ABSTRACT
This chapter highlights results from a program of research testing the motivational properties of the needs for inclusion and differentiation that underlie the optimal distinctiveness model of social identity and the collective self. The findings across different measures of in-group identification and solidarity supported our basic assumption that inclusion and differentiation are separable social motives, in that temporary deprivation of either need engages active efforts to satisfy the need and restore equilibrium. Further, although activating inclusion or differentiation involve opposite types of threat to optimal social identity, either one engages similar mechanisms that serve to restore optimal in-group distinctiveness and inclusiveness. At a more abstract level, these research findings support our general theory that opposing motives underlie a regulatory self-system designed to maintain the individual's connection to social groups that meet basic needs for security and cooperative interdependence with others.
