 Thus far we have examined accounts of social norms that take for granted that a particular norm exists in a population. However, for a full account of social norms, we must answer two questions related to the dynamics of norms. First, we must ask how a norm can emerge. Norms require a set of corresponding beliefs and expectations to support them, and so there must be an account of how these arise. Second, we must investigate the conditions under which a norm is stable under some competitive pressure from other norms. Sometimes, multiple candidate norms vie for dominance in a population. Even if one norm has come to dominate the population, new norms can try to “invade” the existing norm’s population of adherents.