The system in theology which explains the existence of evil by assuming two coeternal principles—one good, the other evil. This dualism is the chief characteristic of the religion of Zoroaster, which assigns all that is good to Ahuramazda, (Ormuzd), and all that is evil to Angromainyush (Ahriman; see Zoroastrianism). Against this dualism, which may have some basic elements in Chaldean mythology, the seer of the Exile protests when accentuating the doctrine that the Lord "formed the light and created darkness," that He "is the Maker of peace and the Creator of evil" (Isa. xlv. 7). The verse has found a place in the daily liturgy (see Liturgy), but with the change of the word "ra"' (evil) into "ha-kol" (all), prompted by an aversion to having "evil" directly associated with the name of God (see Ber. 11b; compare Num. R. xi. 16). The same idea occurs in Lam. (iii. 38, Hebr.): "Out of the mouth of the Most High cometh there not evil and good?" No less emphatic are the Rabbis in their opposition to the dualistic views of Parseeism when they teach that both death and the evil desire ("yeẓer ha-ra'") are agencies working for the good (Gen. R. ix.; compare Sanh. 39a, 91b; Shab. 77b; Maimonides' preface to Mishnah commentary; see Sin).
Zeller ("Gesch. der Philosophie," 2d ed., iii. 250) mistakenly ascribes dualistic notions to the Essenes (Hilgenfeld, "Ketzergesch. des Urchristenthums," 1884, p. 109; see Essenes). On the contrary, Philo ("Quod Omnis Probus Liber," § 12) says that according to them "God only produces what is good, and nothing that is evil." They beheld in life only certain contrasts—opposing tendencies of purity and impurity, of good and evil—and, following ancient Chaldean traditions, placed the one to the right (toward the light) and the other to the left (toward the night) (Josephus, "B. J." ii. 8, § 9; "Clementine Homilies," ii. 15, 33; xix. 12; "Recognitiones," iii. 24)—views which are found also among the Gnostics and the Cabalists (see
Among Jewish philosophers Saadia ("Emunot we-De'ot," ii.) takes especial pains to demonstrate the untenability of dualistic definitions of the Godhead. Were there two creators, it must be assumed that only with the help of the other could each create, and that therefore neither is omnipotent. Light and darkness do not prove the contrary, for darkness is only a negation of light (see Saadia). In the Maimonidean system the difficulty of reconciling the existence of evil with God's unity is solved by the assumption that evil is only negative ("Moreh," iii. 8).