The cosmic struggle of good and evil

Zoroastrians affirm a cosmic struggle between good and evil. The supreme God, Ahura Mazda (the Wise Lord), is wholly good and the source of light, truth, and life; opposed to him stands the destructive spirit, Angra Mainyu (Ahriman), the origin of the lie, darkness, and death. The world is the arena of their conflict, in which every person, by their choices, takes a side. The tradition teaches that the struggle is not eternal in its outcome: good is destined to triumph, evil to be overcome, and creation to be renewed at the end (the frashokereti).

The doctrine's central text is Yasna 30.3-4 in the Gathas, where the two primal spirits are described choosing, from the beginning, between life and not-life, good and evil, a passage scholars of Zoroastrianism, including Mary Boyce and R. C. Zaehner, have debated at length over how strictly dualistic to read it. Some interpreters treat Ahura Mazda and Angra Mainyu as two independent, co-original powers, a stronger dualism; others, especially later Zoroastrian theology, read Angra Mainyu as ultimately a lesser, dependent force whose defeat is assured because Ahura Mazda alone is truly uncreated and supreme, a reading that keeps the tradition closer to a qualified monotheism, and the two interpretations continue to divide scholarly and traditional accounts of the religion's basic theological structure.

This ethical dualism gives Zoroastrian belief its strong moral seriousness: because the cosmos is contested, human choices genuinely matter, and each person's thoughts, words, and deeds add to the side of order or of chaos. The teaching, rooted in the Gathas attributed to Zarathushtra and elaborated in the later Avesta, is often noted for its influence on ideas of a final judgement, resurrection, and the victory of good found in later traditions. It distinguishes Zoroastrianism from both strict monism and any dualism in which evil is co-eternal and undefeated, since here the good God prevails.

One historical school within Zoroastrianism itself, Zurvanism, attempted to resolve the tension in the dualist scheme by positing Zurvan, Infinite Time, as a prior unifying principle from which both Ahura Mazda and Angra Mainyu were born as twin offspring, a myth attested in Sasanian-era sources and in reports by later Christian, Manichaean, and Islamic writers describing Zoroastrian belief they encountered. Zurvanism appears to have had real currency, particularly among the Sasanian priesthood, before the mainstream Zoroastrian tradition that survived into the modern period rejected it as heretical, so that the version of the good-evil struggle now taught by Zoroastrian communities represents the position that outlasted, rather than the only position ever held within, the tradition's own history.