Geiger, in his "Civilisation of Eastern Iranians in Ancient Times", points out that Zoroaster inherited two fundamental principles from his Aryan ancestry.--(1) There is law in Nature. (2) There is conflict in Nature. It is the observation of law and conflict in the vast panorama of being that constitutes the philosophical foundation of his system. The problem before him was to reconcile the existence of evil with the eternal goodness of God. His predecessors worshipped a plurality of good spirits all of which he reduced to a unity and called it Ahuramazda. On the other hand he reduced all the powers of evil to a similar unity and called it Druj-Ahriman. Thus by a process of unification he arrived at two fundamental principles which, as Haug shows, he looked upon not as two independent activities, but as two parts or rather aspects of the same Primary Being. Dr. Haug, therefore, holds that the Prophet of ancient Iran was theologically a monotheist and philosophically a dualist.[4:1] But to maintain that there are "twin"[4:2] spirits--creators of reality and nonreality--and at the same time to hold that these two spirits are united in the Supreme Being,[4:3] is virtually to say that the principle of evil constitutes a part of the very essence of God; and the conflict between good and evil is nothing more than the struggle of God against Himself. There is, therefore, an inherent weakness in his attempt to reconcile theological monotheism with philosophical dualism, and the result was a schism among the prophet's followers. The Zendiks[4:4] whom Dr. Haug calls heretics, but who were, I believe, decidedly more consistent than their opponents, maintained the independence of the two original spirits from each other, while the Magi upheld their unity. The upholders of unity endeavoured, in various ways, to meet the Zendiks; but the very fact that they tried different phrases and expressions to express the unity of the "Primal Twins", indicates dissatisfaction with their own philosophical explanations, and the strength of their opponent's position. S̱ẖahrastānī[5:1] describes briefly the different explanations of the Magi. The Zarwānians look upon Light and Darkness as the sons of Infinite Time. The Kiyūmarṯẖiyya hold that the original principle was Light which was afraid of a hostile power, and it was this thought of an adversary mixed with fear that led to the birth of Darkness. Another branch of Zarwānians maintain that the original principle doubted concerning something and this doubt produced Ahriman. Ibn Ḥazm[5:2] speaks of another sect who explained the principle of Darkness as the obscuration of a part of the fundamental principle of Light itself. [4:1] Essays, p. 303. [4:2] "In the beginning there was a pair of twins, two spirits, each of a peculiar activity". Yas. XXX. 1. [4:3] "The more beneficial of my spirits has produced, by speaking it, the whole rightful creation". Yas. XIX. 9.