seem to have been most complete in Pythagoras. The philosophic living together was its basis. Instruction was oral. Learning was effected by the collision of mind with mind, by objection and answer. It was the Socratic principle inherited from these schools that nothing passed muster for knowledge which did not stand the test of cross-examination:(406) but an unchangeable text was utterly unsuited, according to Plato, to debate the question under treatment in such fashion, while on the other hand the mind of the reader was passive in receiving the impression which it conveyed. On neither side therefore did the conditions of knowledge exist, but this was reached under the circumstances of personal intercourse above mentioned, and might be recalled in the written form to the minds of those who had thus first attained it. Down to the end of Greek philosophy the same conception as to the method of teaching prevailed. Ammonius Sakkas, the founder of Neoplatonism, delivered his doctrine only by word of mouth, which his chief disciples, Erennius, Origines, and Plotinus, engaged not to make public.(407) It was when one of them, Erennius, had broken this promise, that another, Plotinus, after delivering lectures at Rome, wrote down his philosophy; but his scheme was to carry it out by collecting his disciples together in one city, and thus realising Plato’s republic. CHAPTER XIV. THE CHRISTIAN CHURCH AND THE GREEK PHILOSOPHY. PART II. The mind of the next great teacher who arose in Greece after Plato presented an almost complete contrast to that of the master under whom he had so long studied. Aristotle’s power consisted in a parallel development of two forces which do not often coexist.(408) He joined together a rare degree of consistent philosophic thinking with an equally rare degree of accurate observation. This double faculty is shown in what he effected. He made the sciences of logic, ethics, and psychology: he built up those of natural history and politics with the wealth of knowledge which his experience had accumulated.(409) Thus his analytic and synthetic genius embraced the whole range of human knowledge then existing. As Plato threw his vivid fancy and imagination and his religious temper into everything which concerned the human spirit, so Aristotle fixed his gaze upon nature, which with him in all its manifestations was the ultimate fact. As Plato rose from the single being to his conception of the true, the good, the beautiful, of which the Idea to him was everything, so Aristotle, steadfastly discarding his master’s doctrine of Ideas, took his stand on the single being, examining it with the closest observation and the subtlest thought, and the knowledge thus conveyed to him is everything. Plato’s conception of God is that of the great world-former, orderer, and ruler: Aristotle’s conception of God is that of a pure intelligence, without power, an eternal, ever-active, endless, incorporeal substance,