There is another expression which must be considered in connexion with the mediaeval doctrine of deification.  This is the intellectus agens, or [Greek:  nous poietikos], which began its long history in Aristotle (De Anima, iii. 5).  Aristotle there distinguishes two forms of Reason, which are related to each other as form and matter.  Reason becomes all things, for the matter of anything is potentially the whole class to which it belongs; but Reason also makes all things, that is to say, it communicates to things those categories by which they become objects of thought.  This higher Reason is separate and impassible ([Greek:  choristos kai amiges kai apathes]); it is eternal and immortal; while the passive reason perishes with the body.  The creative Reason is immanent both in the human mind and in the external world; and thus only is it possible for the mind to know things.  Unfortunately, Aristotle says very little more about his [Greek:  nous poietikos], and does not explain how the two Reasons are related to each other, thereby leaving the problem for his successors to work out.  The most fruitful attempt to form a consistent theory, on an idealistic basis, out of the ambiguous and perhaps irreconcilable statements in the De Anima, was made by Alexander of Aphrodisias (about 200 A.D.), who taught that the Active Reason “is not a part or faculty of our soul, but comes to us from without”—­it is, in fact, identified with the Spirit of God working in us.  Whether Aristotle would have accepted this interpretation of his theory may be doubted; but the commentary of Alexander of Aphrodisias was translated into Arabic, and this view of the Active Reason became the basis of the philosophy of Averroes.  Averroes teaches that it is possible for the passive reason to unite itself with the Active Reason, and that this union may be attained or prepared for by ascetic purification and study.  But he denies that the passive reason is perishable, not wishing entirely to depersonalise man.  Herein he follows, he says, Themistius, whose views he tries to combine with those of Alexander.  Avicenna introduces a celestial hierarchy, in which the higher intelligences shed their light upon the lower, till they reach the Active Reason, which lies nearest to man, “a quo, ut ipse dicit, effluunt species intelligibiles in animas nostras” (Aquinas).  The doctrine of “monopsychism” was, of course, condemned by the Church.  Aquinas makes both the Active and Passive Reason parts of the human soul.  Eckhart, as I have said in the fourth Lecture, at one period of his teaching expressly identifies the “intellectus agens” with the “spark,” in reference to which he says that “here God’s ground is my ground, and my ground God’s ground.”  This doctrine of the Divinity of the ground of the soul is very like the Cabbalistic doctrine of the Neschamah, and the Neoplatonic doctrine of [Greek:  Nous] (cf.  Stoeckl, vol. ii. p. 1007).  Eckhart was condemned for saying, “aliquid est in anima