Social identity theory
Part of who we are comes from the groups we belong to.
What it means
A theory holding that people derive part of their self-concept and self-esteem from membership in social groups, and are therefore motivated to see their in-groups as positively distinct from out-groups. Three processes are central: social categorization (sorting people into groups), social identification (adopting the group as part of the self), and social comparison (evaluating one's group against others). Because positive group distinctiveness bolsters self-esteem, even arbitrary, minimal group assignments produce in-group favoritism in resource allocation. The theory explains discrimination, intergroup conflict, conformity to group norms, and collective action without requiring material self-interest. It is one of the most generative frameworks in social psychology and the parent of self-categorization theory.
Examples
In the minimal-group experiments, people assigned to meaningless groups by a coin flip still allocated more rewards to their own group.
Supporters say 'we won' after a match they watched from the sofa and 'they lost' after a defeat. The club's standing is doing real work in their own self-esteem.
Weeks after a reorganisation, two teams in the same company are guarding information from each other, though nobody's bonus depends on it. The new labels alone were enough.
First described in Tajfel & Turner (1979).