Ahura Mazda, Angra Mainyu, and Cosmic Dualism

At the doctrinal core of Zoroastrianism lies a radical cosmic dualism, most explicitly articulated in Yasna 30 of the Gathas, where Zoroaster describes two primordial spirits, twins, who at the beginning chose opposite paths: Spenta Mainyu, the "Bounteous Spirit," identified with or closely associated with Ahura Mazda himself, who chose truth and life, and Angra Mainyu, the "Destructive" or "Hostile Spirit" (later known in Middle Persian as Ahriman), who chose the lie and death. This is not a dualism of two co-equal, co-eternal gods in symmetrical balance, as it is sometimes popularly caricatured; Ahura Mazda is consistently presented in the Gathas as the sole uncreated creator, the source of Spenta Mainyu's goodness, while Angra Mainyu's destructive nature is his own free, culpable choice rather than an independent metaphysical principle equal in status to the divine. The relationship between Ahura Mazda and Angra Mainyu, and how strictly to read Ahura Mazda as author of both spirits, became one of the most contested points in the later history of Zoroastrian theology, producing markedly divergent solutions across different periods and sects.