From the true God, the eternal Absolute, proceeds the _nous_, a term which has been variously rendered as Reason, Intellect, Intelligence, or Spirit, this last being the term which Dr. Inge regards as the best expression (Inge: _Plotinus._ ii. p. 38), and this _nous_ is fairly equivalent to the Philonic and Christian _Logos_. An external emanation is necessitated in order that the First Cause may remain unchanged which would not be the case if it had once not been a source and then had become the source of emanation; there can be no “becoming” in the First Cause. The emanation is of the same nature as its cause, but is projected into the world of phenomena. It is self-existent, eternal, and perfect, and comprehends within itself the “spirit world,” the objects of abstract reason, the whole of the reality which lies behind the world of phenomena; the things perceived are only the shadows of these real ones. It perceives, not as seeking and finding, but as already possessing (id. 5. 1. 4.), and the things perceived are not separate or external but as included and apprehended by immediate intuition (id. 5. 2. 2.) From the _nous_ proceeds the _psyche_, the principle of life and motion, the world soul which is in the universe and which is shared by every living creature. It also knows, but only through the processes of reasoning, by means of separating, distributing, and combining the data obtained by sense perception, so that it corresponds in function to the “common sense” of Aristotle, whilst the _nous_ shows the functions which are attributed to it by Aristotle and has the character which Alexander reads into Aristotle. The work of Plotinus was continued by his pupil Porphyry (d. 300 A.D.) who taught at Rome, and is chiefly noteworthy as the one who completed the fusion of Platonic and Aristotelian elements in the neo-Platonic system, and especially as introducing the scientific methods of Aristotle. Plotinus had criticized adversely the Aristotelian categories (_Enn._ vi.), but Porphyry and all the later neo-Platonists returned to Aristotle. Indeed, he is best known to posterity as the author of the _Isagoge_, long current as the regular introduction to the logical Organon of Aristotle. Then came _Jamblichus_ (d. 330), the pupil of Porphyry who used neo-Platonism as the basis of a pagan theology; and finally Proklus (d. 485) its last great pagan adherent who was even more definitely a theologian.