 Philosophers have taken a different approach to norms. In the literature on norms and conventions, both social constructs are seen as the endogenous product of individuals’ interactions (Lewis 1969; Ullmann-Margalit 1977; Vandershraaf 1995; Bicchieri 2006). Norms are represented as equilibria of games of strategy, and as such they are supported by a cluster of self-fulfilling expectations. Beliefs, expectations, group knowledge and common knowledge have thus become central concepts in the development of a philosophical view of social norms. Paying attention to the role played by expectations in supporting social norms has helped differentiate between social norms, conventions, and descriptive norms: an important distinction often overlooked in the social science accounts, but crucial when we need to diagnose the nature of a pattern of behavior in order to intervene on it.