 Social ontology is the study of social entities and properties. But which things are social? How are they distinguished from those that are not social? Not every theory in social ontology needs to make this distinction—but many rely on it. Michael Bratman, for instance, analyzes “shared intentions” of a group in terms of the knowledge and intentions of individual members of the group (Bratman 1993, 2014). His project is designed to remove the mystery behind shared intention by analyzing it in terms of non-social mental states of individual people. More generally, “psychologistic” theories of the social world sharply distinguish the social from the non-social. These theories—descendants of Mill 1843—hold that all social facts are determined by the psychological states of individual people.