Social groups cannot be identified with sets of people in the mathematical sense

What are social groups? One debate in the literature concerns the kind of entities that social groups are: collections, classes, sets, fusions, structures, or some other kind of entity. It may seem natural to think of a group as a set of people in the mathematical sense. However, groups can persist through changes in membership, while sets are generally understood as having their members essentially (see Sharvy 1968, Ruben 1985, Uzquiano 2004, Sheehy 2006). Effingham (2010) proposes an account t