Ethical dualism, also called moral dualism, is the view that good and evil are antagonistic forces that govern the world and are locked in a perpetual conflict.

In relation to the theory of dualism in its broader philosophical and metaphysical sense, it is useful to point out how ethical dualism differs from it or what it adds to it.

Dualism is a theory which interprets any given situation in terms of two contrasting elements, which from a metaphysical point of view comes to imply that reality consists of two fundamental types of existence which cannot be reduced to each other. Examples of metaphysical dualisms are those between spirit and matter, God and the world, or, as theorized by Descartes, between thought and extension.

Ethical dualism, on the other hand, highlights the moral dimension instead or in addition to the metaphysical one, and envisions an inherent situation of conflict between two antagonistic forces, like light and darkness, Good and Evil.

One of the most known and clear-cut interpretations of ethical dualism is the one conceptualized by Zoroastrianism, the ancient Persian religion, which bases its thought on the figure of the prophet Zoroaster (or Zarathustra), who claimed the existence of two original and contrasting principles, Ahura Mazda and Ahriman, respectively representing the forces of Good and Evil. The world is therefore identified as the battleground between these two contrasting entities, also associated with light and darkness.

Each man and woman, for his or her self, select either of the two […] The worst mind shall be for the wrongful, and the best mind shall be for the righteous.

— Yasna 30, 17 Gatha Hymns

Also, in Zoroastrianism, there is no room for reconcilement between the two opposing forces of good and evil: