Covenants without Swords: Group Identity, Norms, and Communications in Social Dilemmas

In one-shot social dilemma experiments, cooperation rates dramatically increase if subjects are allowed to communicate before making a choice. There are two possible explanations for this 'communication effect'. One is that communication enhances group identity, the other is that communication elicits social norms. This article discusses both views and argues in favor of a norm-based explanation.