The problem of group and sub-group can be approached either descriptively or genetically. If we take the former angle, we see every large group divided indefinitely into small, conflicting, overlapping, and infinitely various sub-groups. Much of the complexity of our society consists in this overlapping, by which the individual belongs to many groups at once, so that his mind cannot attain complete unity, and none of his groups can possess him wholly. A man belongs to a family, a city, a profession, a church, a school alumni body, a nation and an international peace society. In addition, he may join a labor union, a chamber of commerce, or a half dozen fraternal orders. His mind is a perfect maze of group attitudes; he shifts from one group to another as interests or contiguity impel him. In the same way, a large group such as a political party includes members from different sections of the country, different economic strata, different churches, and so on. The group mind, as a category in this situation, is purely a functional unity, which works in and through its individual members and through its smaller groups of individuals in exactly the same way. I quote Dr. Singer: [38]“My world is highly organized—groups within groups, and groups within these,” for that is the scientific, realistic view of the social world. Various classifications of groups have been devised by students of the problem, useful for their different purposes. Cooley speaks of primary and secondary groups, those in which men and women are born and grow, and the larger integrations into which the smaller, more natural groups enter. Miller prefers [39]“Vertical and horizontal groups,” the former being the natural divisions which include all classes, such as the nation; the latter a caste or class grouping. Hayes calls them personal and impersonal groups, apparently meaning much the same as Professor Cooley by the terms primary and secondary. Probably the most useful mode of classification is the genetic, beginning with the family, and then expanding according to the particular situation in view—in the primitive group to the clan, tribe and confederacy; in the civilized to the school, the interest group, the religious affiliation, the political nation, the international ideals and bonds of union. Whatever be the more or less arbitrary mode of classification, we see that, except for the supposititious primitive horde, groups are never single nor simple. They resemble rather the physical organism or the mind of the individual, either of which is necessarily complex. Group minds exist and grow by progressive integration of the lesser into the greater, from the individual up to the greatest possible bodies of human beings.