His world OF ours is a world of opposites. There is light and shade, there is heat and cold, there is good and evil, there is God and the Devil. The dualistic conception of nature has been a neces sary phase in the evolution of human thought. We find the same views of good and evil spirits prevailing among all the peoples of the earth at the very beginning of that stage of their development which, in the phraseology of Tylor, is commonly called Animism. But the principle of unity dominates the development of thought. Man tries to unify his conceptions in a consistent and barmo nions Monism. Accordingly, while the belief in good spirits tended towards the formation Of the doctrine of Monotheism, the belief in evil spirits led naturally to the acceptance of a single supreme evil deity, conceived as embodying all that is bad, destructive, and immoral.