 Social norms, like many other social phenomena, are the unplanned result of individuals’ interaction. It has been argued that social norms ought to be understood as a kind of grammar of social interactions. Like a grammar, a system of norms specifies what is acceptable and what is not in a society or group. And, analogously to a grammar, it is not the product of human design. This view suggests that a study of the conditions under which norms come into being—as opposed to one stressing the functions fulfilled by social norms—is important to understand the differences between social norms and other types of injunction (such as hypothetical imperatives, moral codes, or legal rules).