In-groups acquire definition only through comparison and contrast with out-groups

Evidence

This form of depersonalization occurs in a comparative context between in-groups and out-groups. That is, the categorization of the self as a group member is more likely to occur insofar as the perceived differences between in-group members are less than the perceived differences between in-group and out-group members. Accordingly, social identity theory posits that in-groups cannot be defined in isolation from out-groups, but rather that they gain their definition from comparisons and contrasts to out-groups. Because the self is defined at the level of the in-group, value is derived from maximizing positive distinctiveness between in-groups and out-groups. Thus, intergroup status differentials and one’s group having higher status are critical. — Roderick M. Kramer, Geoffrey J. Leonardelli, Robert W. Livingston, Social Cognition, Social Identity, and…, 1608

Categorization

• corroborated: 2 independent passages support this claim — Roderick M. Kramer, Geoffrey J. Leonardelli, Robert W. Livingston, Social Cognition, Social Identity, and…, 1608