Here Plotinus avowedly follows the teaching of Plato, who, in the _Timaeus_, describes Being or Substance as composed by mingling the indivisible and unchanging with the divisible and corporeal principle.[448] And, although there is no express reference, we know that in placing soul between the two, he was equally following Plato. It is otherwise in the next essay, which undertakes to give a more explicit analysis of psychical phenomena.[449] The soul, we are told, consists, like external objects, of two elements related to one another as Form and Matter. These are reason and sense. The office of the former is, primarily, to enlighten and control the latter. Plato had already pointed to such a distinction; but Aristotle was the first to work it out clearly, and to make it the hinge of his whole system. It is, accordingly, under the guidance of Aristotle that Plotinus proceeds in what he has next to say. Just as there is a soul of the world corresponding to our soul, so also, he argues, there must be a universal objective Reason outside and above the world. In speaking of this Reason, we shall, for clearness’ sake, in general call it by its Greek name, Nous. Nous, according to Aristotle, is the faculty by which we apprehend abstract ideas; it is self-thinking thought; and, as such, it is the prime mover of Nature. Plotinus adopts the first two positions unreservedly, and the third to a certain extent; while he brings all three into combination with the Platonic theory of ideas. It had always been an insuperable difficulty in the way of Plato’s teaching that it necessitated, or seemed to necessitate, the unintelligible notion of ideas existing without any mind to think them. For a disciple of Aristotle, the difficulty ceases to exist if the archetypal essences assumed by Plato are conceived as residing in an eternal Nous. But, on the other hand, how are we to reconcile such an accommodation with Aristotle’s principle, that the Supreme Intelligence can think nothing but itself? Simply by generalising from the same master’s doctrine that the human Nous is identical with the ideas which it contemplates. Thought and its object are everywhere one. Thus, according to Plotinus, the absolute Nous embraces the totality of archetypes or forms which we see reflected and embodied in the material universe. In thinking them, it thinks itself, not passing from one to the other as in discursive reasoning, nor bringing them into existence by the act of thought, but apprehending them as simultaneously present realities.