 Rawls conceives of promises not as sui generis moral actions, but as essentially institutional artifacts, and thus promissory obligations as institutional obligations, grounded in the same manner as all such obligations. These institutions are comprised of sets of rules that prescribe and proscribe certain sorts of behavior for the participants in the institution. The dicta of the rules are the contents of moral obligations. Rawls in turn grounds institutional obligations in what he calls the principle of fairness.