For example, a utilitarian (someone who prescribes maximizing expected human welfare) might partially justify keeping a promise on the grounds that there is a social norm in favor of promise keeping. The utilitarian is perfectly free to appeal to the fact that people generally keep their promises and expect others to do so as well. Part of his reason for keeping a promise may be that there is a general practice, moreover, a social norm, in its favor. Ultimately, however, he will appeal to the expected difference an action makes to human welfare. Social norms may figure into this calculation as relevant empirical facts. The sort of justifications I wish to examine here are not of this kind. There is no background moral theory that buttresses the appeal to a social norm. The norm alone is thought to be enough of a justification for the actions we are considering.