Sun-Grounding Social Sciences in Cognitive Sciences36 Paul Thagardperspective of the natural sciences, the idea of mutual constitution is highly puzzling, because constitution in physical systems is a unidirectional, asymmetric part-whole relation. Particles such as protons make up atoms, which make up molecules, which make up cells, which make up tissues, which make up organs, which make up organisms, which make up species. Analogously, in accord with methodological individualism, it would seem that people make up social groups, not vice versa. Can sense be made of the idea that social groups constitute people? Here is the key insight to resolve this seeming conundrum: the actions of groups result from the actions of individuals who think of themselves as members of groups. What makes a group a group is not the sort of physical bonding that makes a group of cells into an organ. Rather, social bonds are largely psychological and arise from the fact that the individuals in the group have mental representations, such as concepts, that mark them as members of the group. The bonding process is not purely psychological, however, as it can also include various kinds of physical interactions that are social, linguistic, or both, such as participating in rituals and legal contracts, or even just making eye contact. These interactions tie people together into groups when they result in mental representations (affective as well as cognitive) through which individuals come to envision themselves as part of the group. Without such envisioning, the group cannot continue to function collectively. For example, by going together to church, school, and work bees, church members reinforce the beliefs and attitudes that mark them as members in contrast to other groups. To take a simpler example, a marriage is not simply a legal arrangement, but is also a social group that depends on the development and maintenance of emotional bonds through ongoing emotional interactions (Gottman, Tyson, Swanson, Swanson, & Murray, 2003). This account does not, however, reduce the social to the psychological, because the psychology of individuals cannot be understood without appreciating the centrality of the social to the self. Many psychologists have observed that group membership and distinctions between in-groups and out-groups are an important part of self-identity (Tajfel, 1974;Brewer & Yuki, 2007). What individuals do is greatly affected by how they think of themselves in relation to ongoing interactions with various groups. Individuals are social in that a person's thinking and behavior depends substantially on representation of and interaction with other people. It is an exaggeration to conclude from such interactions that the social constitutes the individual in the way that individuals constitute groups; for a rigorous analysis of such constitution, see Findlay and Thagard (2011).