One property of social relations on which effective norms depend is what I will call closure. In general, one can say that a necessary but not sufficient condition for the emergence of effective norms is action that imposes external effects on others

DEFINE: Introduces 'closure' as a technical condition for effective norms, and distinguishes external effects as a necessary but not sufficient condition. Builds on: "Effective social norms both enable and constrain community action."

Coleman, SocialCapitalCreation-1988, loc. 114