Dualism, or Manichæism, the doctrine that there are two opposite and independently existing principles which go to constitute every concrete thing throughout the universe, such as a principle of good and a principle of evil, light and darkness, life and death, spirit and matter, ideal and real, yea and nay, God and Devil, Christ and Antichrist, Ormuzd and Ahriman.
Definition taken from The Nuttall Encyclopædia, edited by the Reverend James Wood (1907)
Dryden, John * Du Barry, Countess