Originally published in 1956, this book provides a clear, scholarly, introduction to the main tenets of Zoroastrian dualism presented largely in the words of the Zoroastrian texts themselves. The book demonstrates the essential reasonableness of Zoroastrian dualism, which is the dualism of a good and an evil spirit, and to show what the means in everyday life and how it is philosophically justified. There are chapters on cosmology, the relation of man to God, the nature of religion, ethics, sacraments and sacrifice, the soul's fate at death and eschatology.