I define a social norm as a regularity in behavior whose persistence is causally explained by the existence of sanctioning attitudes of participants toward violations—without these sanctions, individuals have motive to violate the norm. I show how a universal precept "When in circumstances S, do action F" can be sustained by the conditional preference of each to conform, given that others do, of a convention, and also reinforced by the sanctions of a norm. I observe that a precept with moral force can be reinforced by a social norm. I then consider constitutive norms and show by means of an example, competitive figure skating, how a type of activity or practice G can have a constitutive norm NG. An ongoing activity in a community is engagement in that practice only if NG is reinforced as a social norm by participants. I apply this to the case of assertion: the speech act type Assertion has a constitutive norm NA, and a practice of making speech acts in a community is one of making assertions only if it is controlled by NA enforced by the sanctions of a social norm.