Hume's account of how conventions establish artificial virtues is an integral part of his attempt to naturalize mo-rality. His argument would be a failure if conventions were irreducibly normative. Hume's conventions, though, are not norms but acts of agreement that establish norms. Their basis is men's sense of interest and their ability to communicate it. No norm or rule can guarantee the success of this communication. The analysis of promises brings this to light, since no rule about forms of words can any more secure that a promise is made, if not backed by the communication of intentions.