Among the ancient Greek philosophers we find “matter” (ὕλη) identified with “vacuum” or “empty space” (το κενόν) and this again with “nothingness” or non-being (τὸ μη νὀ). Now the concept of evil is the concept of something negative—a privation of goodness, of being or reality. Thus the notion of evil came to be associated with the notion of matter. But the latter notion is not really negative: it is that of a formless, chaotic, disorderly material. When, therefore, the Manicheans attributed a positive reality to evil—conceiving it as the principle of all disorder, strife, discord—they naturally regarded all matter as the expression of the Evil Principle, in opposition to soul or spirit as the expression of the Good Principle. The Manichean philosophy of Evil, a product of the early Christian centuries, has been perhaps the most notable alternative or rival system encountered by the theistic philosophy of Evil; for, notwithstanding the fantastic character of its conceptions Manicheism has reappeared and reasserted itself repeatedly in after ages, notably in the Middle Ages. Its prevalence has probably been due partly to the concreteness of its conceptions and partly to a certain analogy which they bear towards the conception of Satan and the fallen angels in Christian theology. In both cases there is the idea of conflict, strife, active and irreconcilable opposition, between the powers of good and the powers of evil. But there the analogy ends. While in Christian theology the powers of evil are presented as essentially subject to the Divine Omnipotence, in Manicheism the _Evil Principle_, the _Summum Malum_, is presented as a supreme, self-existent principle, essentially independent of, as well as antagonistic to, the Divine Being, the _Summum Bonum_. Since there is evil in the world, and since good cannot be the cause of evil—so the Manicheans argue—there must be an essentially Evil First Principle which is the primary source of all the evil in the universe, just as there is an essentially Good First Principle which is the source of all its good. Everything in the world—and especially man himself, composed of matter and spirit—is the expression and the theatre of the essential conflict which is being ever waged between the Good and the Evil Principle. Everywhere throughout the universe we find this dualism: between spirit and matter, light and darkness, order and disorder, etc.