Building on Adam Smith’s moral theory, the paper discusses effects of group size on moral standards. The key concepts of Smith’s theory, sympathy and the impartial spectator, provide a basis here fore, as they presuppose a moral community, i.e. a group of people bound together via common experience and values. As this group increases in size, common experience will become scarce, leading to a decrease in the habitual sympathy among its members. Consequently moral communities sharing related impartial spectators will be of limited size. In order to achieve coordination among the members of a polymorphic society, the law regulates which norms should be binding for it. Following Smith, common law seems to bear superior features compared to other legal systems in making use of juries, thereby resembling the internal, moral judgement process. Limits to the application of common law are discussed.