Approaches to the study of international politics grounded in ­logics of the social require an idea of the social as political, an idea of social institutions as meaningful entities in the practice of politics apart from their role as institutional constraints on individual political actors. John Ruggie uses the term “social purpose” in this context to link constructivism with late nineteenth- and early twentieth-century Continental social theorists such as Durkheim and Weber. Whether or not one accepts this particular understanding of the social as political, a social constructivist approach requires that one have some equivalent idea. Without such an idea one is left either with purely individualist motivations for political action, or without any source of change in political patterns and structures, which is to say without any politics at all. And even purely individualist motivations for individual action reflect social purpose, to the extent that individual identities and interests are socially constructed.

As I argue below, a common feature of constructivist ideas of the social as political is the concept of a public interest, defined as a set of political goals intersubjectively held within a social group, goals held for the group rather than (or as well as) for the members of the group as individuals. Any group of people whose political identity is, in whole or in part, focused on the group, and who hold common political goals for the group, have a public interest.