We have seen some of the aspects of Pre-Islamic Persian thought; though, owing to our ignorance of the tendencies of Sāssānīde thought, and of the political, social, and intellectual conditions that determined its evolution, we have not been able fully to trace the continuity of ideas. Nations as well as individuals, in their intellectual history, begin with the objective. Although the moral fervour of Zoroaster gave a spiritual tone to his theory of the origin of things, yet the net result of this period of Persian speculation is nothing more than a materialistic dualism. The principle of Unity as a philosophical ground of all that exists, is but dimly perceived at this stage of intellectual evolution in Persia. The controversy among the followers of Zoroaster indicates that the movement towards a monistic conception of the Universe had begun; but we have unfortunately no evidence to make a positive statement concerning the pantheistic tendencies of Pre-Islamic Persian thought. We know that in the 6{th} century A.D., Diogenes, Simplicius and other Neo-Platonic thinkers, were driven by the persecution of Justinian, to take refuge in the court of the tolerant Anūs̱ẖīrwān. This great monarch, moreover, had several works translated for him from Sanskrit and Greek, but we have no historical evidence to show how far these events actually influenced the course of Persian thought. Let us, therefore, pass on to the advent of Islām in Persia, which completely shattered the old order of things, and brought to the thinking mind the new concept of an uncompromising monotheism as well as the Greek dualism of God and matter, as distinguished from the purely Persian dualism of God and Devil. PART II. Greek Dualism. CHAP. II. THE NEO-PLATONIC ARISTOTELIANS OF PERSIA. With the Arab conquest of Persia, a new era begins in the history of Persian thought. But the warlike sons of sandy Arabia whose swords terminated, at Nahāwand, the political independence of this ancient people, could hardly touch the intellectual freedom of the converted Zoroastrian.