The tendencies which were at work in Philo were also leavening Greek thought outside Jewish circles and all schools of philosophy show a growing definiteness in their assertion of One God eternal and invariable, as the source and First Cause of the universe. It is a recognition of the principal of uniformity in nature and of the necessity of accounting for the cause of this uniformity. The Gnostic sects, which were of philosophical origin, simply show the definite acceptance of this First Cause and, having accepted it as on a plane far removed above imperfection and variation, suggest intermediary emanations as explaining the production of an imperfect and variable universe from a primary source which is itself perfect and unchanging. The descriptive accounts of the successive emanations, each less perfect than that from which it proceeds, which ultimately produced the world in which we perceive phenomena, are different in different Gnostic systems, often crude enough and grotesque in our eyes, and frequently drawing from Christianity or Judaism or some other of the oriental religions which were then attracting the attention of the Roman world. But these details are of minor importance. All Gnostic theories bear witness to the belief that there is a First Cause, absolutely real, perfect, eternal, and far removed above this world of time and space, and that some emanation or emanations must have intervened to connect the resultant world, such as we know it, with this sublime Cause: and such belief indicates in crude form a general conviction which was getting hold of all current thought in the early centuries of the Christian era. Complementary to this was the psychological teaching represented by the Aristotelian commentator Alexander of Aphrodisias who taught at Athens, A.D. 198-211. His extant works include commentaries on the first book of the Analytica Priora, on the Topica, Meteorology, _de sensu_, the first five books of the Metaphysics and an abridgment of the other books of the Metaphysics, as well as treatises on the soul, etc. Over and over again his treatise on the soul and his commentaries are translated into Arabic, paraphrased, and made the subject of further commentaries, until it seems that his psychology is the very nucleus of all Arabic philosophy, and it is this which forms the main point of the Arabic influence on Latin scholasticism. It becomes indeed absolutely essential that we understand the Alexandrian interpretation of the Aristotelian psychology if we are to follow the oriental development of Greek science.