Manicheism, as represented by the Cathari and Albigenses, was a strong power in St Thomas's time. After a prevalence of more than a thousand years, it is entirely dead in the West. As the plague takes the place of other sicknesses, so Materialism has killed Manicheism. In old times, Matter baffled Mind; and Mind was tempted to pronounce Matter evil. Now the empire of Mind over Matter is consolidated and daily spreading; and Mind is apt to fall in love with its creature, Matter, to identify itself with it, and finally to worship it. There is a strand of Manicheism in those two lost causes, Calvinism and Puritanism.
Of God and His Creatures: 4.56