DUALISM: In general, any twofold classification that admits of no intermediate degrees; in philosophy, the theory that the facts of the world are to be explained by two independent and eternally coexistent principles, viz., mind and matter (see DESCARTES, RENE); in theology, the view that there are two mutually hostile forces in the world, one the creator of all things good, both in nature and morals, the other the source of all evil and sin.
It has been claimed that all heathen, or at least all polytheistic, religions are of a dualistic character; but this is true only to a limited extent. To be sure, in polytheistic religions there is always the belief in demons. These are the enemies of man, and appear as the personification of disease, death, and all natural phenomena harmful to man (see COMPARATIVE RELIGION, VI., 1, a, § 4). However, though they have a certain influence in the world of nature, they are never supposed to influence the moral order of the world, and so are not responsible for moral evil. Hence, such religions can not be called dualistic in the proper sense of the word. Throughout heathendom there is only one religion that can be said to be dualistic, and that is Zoroastrianism (q.v.). According to the teachings of Zoroaster, there are two personal creative forces in the world: (1) Ahura Mazda, the good spirit, the creator of gods and men and all that is beneficent in nature, and the guardian of the moral order of the world; (2) Angra Mainyu, the evil spirit, the creator of demons and all that is injurious in nature, and the source of all evil and sin. He is the enemy of Ahura Mazda and tries to overthrow the moral order by tempting men to sin, and thus making them his allies. This conflict between the two spirits continues till the end of the world; and this dualism extends through the whole of nature. Everything that exists belongs either to the creation of Ahura Mazda or to that of Angra Mainyu; and only man, by reason of a free will, can choose for himself one master rather than the other, though morally he belongs on the side of Ahura Mazda, his creator. It must be added that this dualism is not perfect in the sense that the two powers are equally matched. With his superior wisdom Ahura Mazda has the advantage from the beginning, and is to triumph over his enemy in the end. Then Angra Mainyu, with all that he created, shall be destroyed, and his followers, after they have been purified by a great world-fire, shall return to their creator. Thus the spirit of goodness reigns supreme in the end, and the dualism is overcome. See GNOSTICISM, § 6.
Bibliography: The literature of specific forms of dualism will be found under CELIBACY, MANICHFANS, NEW MANICHEANS. ZOROASTRIANISM. For further treatment consult the works on the hist. of philo.Rophy,by F. Ueberweg, New York, 1894, J. E. Erdmann, London, 1893, and W. Windelband, ib. 1893. Also KL, iii. 2092-96.