The shortest answer to the question about what kind of unification is present in the totality lies in a direct reference to the phenomena. And here we truly are concerned with ultimate facts. But we are not thereby relieved of the task of considering this kind of combination more carefully, in order to bring into relief its characteristic differences from other kinds, especially since false characterizations and confusions of it with other species of relations have been an all too common occurrence. To this end we shall test a series of possible theories, some of which have actually been advanced. Each of these theories characterizes the collective unification in a different way and, in relation thereto, seeks also to explain in a different way the origin of the concepts multiplicity and number.