The Platonic form of realism grew out of a distinction between the real and the phenomenal, which in its turn it tended to accentuate. The visible world of concrete individuals was regarded as phenomenal and transitory: the invisible world of intelligible essences was real and permanent: the one was _genesis_, or “becoming;” the other, _ousia_, or “being.”[557] The distinction played a large part in the later history of Platonism:[558] and whereas in the view of Aristotle the species, or smaller class, as being nearer to the concrete individuals, was more _ousia_ than the genus, or wider class, in the later philosophy, on the contrary, that was _ousia_ in its highest sense which was at the farthest remove from the concrete, and filled the widest sphere, and contained the largest number of other classes in itself: it was the _summum genus_.[559] Hence Plotinus says that in respect of the body we are farthest from _ousia_, but that we partake of it in respect of our soul; and our soul is itself a compound, not pure _ousia_, but _ousia_ with an added difference, and hence not absolutely under our control.[560] Of these two meanings of _ousia_, namely “species” and “genus,” the former expressing the whole essence of a class-name or concept, the latter part of the essence, the former tended to prevail in earlier, the latter in later Greek philosophy. In the one, the knowledge of the _ousia_ was completely unfolded in the definition, so that a definition was itself defined as “a proposition which expresses the _ousia_:”[561] in the latter, it was only in part so unfolded, so that it is necessary for us to know not only the _ousia_ of objects of thought, for example, whether they fall within or without the class “body,” but also the species (εἴδη).[562] But in the one meaning as in the other, the members of the same class, or the sub-classes of the same wider class, were spoken of as _homoousioi_: for example, there was an argument that animals should not be killed for food, on the ground that they belong to the same class as men, their souls being _homoousioi_ with our own:[563] so men are _homoousioi_ with one another, and Abraham washed the feet of the three strangers who came to him, thinking them to be men “of like substance” with himself.[564]