 Agreement, according to some historical theories, is the source of law, language, and the state (see section  1.1, and   also sections A.1 and  A.2.1 of the supplement).  Agreement still plays a role in contemporary theories of some social phenomena, but that role is typically to ground the obligations associated with phenomena. For instance, according to the “will theory of contract”, contractual obligations are grounded by the intentional choices of each party to be bound to a commitment (see Fried 1981, Barnett 1985). When it comes to setting up social categories, it seems less likely that actual agreements are available to be their metaphysical sources. Instead, even theories that are putatively agreement-based tend to place agreement in a different role. Gauthier 1986, for instance, advances an agreement-based theory of morality. By his account, however, the justification for moral claims is based on what people rationally would agree to: idealized agreements, rather than actual ones, serve as the basis for moral categories.