  In addition to having substances as parts, groups have them as members. On McTaggart’s view, parthood is not sufficient for membership. Although the parthood relation is transitive, the membership relation is not. According to McTaggart, whenever there are some substances, they also form a group, and whenever there are some groups they too from a group. Although there is a universal substance, no group contains all the other groups. Finally, no group contains itself as a part. McTaggart appears to have an iterative conception of the group-theoretic hierarchy, although he denies that there are groups with only one or fewer members.