Dualism

Dualism is a family of views that explain a domain or phenomenon through a fundamental division into two principles, substances or aspects regarded as irreducible to one another. It is usually contrasted with monism, which rejects any basic division, and with forms of pluralism that admit more than two principles.

The term comes from the Latin for two and entered philosophical vocabulary in the eighteenth century, although its use is older. Thomas Hyde is credited with applying it in a theological sense to Persian religion, and Pierre Bayle used it in 1697 for Manichaeism, which opposes Good and Evil without reconciliation. Christian Wolff later applied it to philosophy in 1734 to describe Descartes's system, which separates extended matter, including the body, from thinking substance, the mind or soul.

Dualist ideas take many forms. In religion, Zoroastrianism posits a divine principle of good and another of evil, and Manichaeism identifies light and spirit with good and darkness and matter with evil. In philosophy, Plato contrasts the eternal, unchanging world of Forms with the changing, perishable sensible world. In Chinese thought, yin and yang are understood as opposed yet complementary forces. In the modern period, Descartes's mind–body dualism became a central topic of the philosophy of mind.

Dualisms often stress separation and sometimes antagonism between their terms, but the word is also used broadly for theories in which the two sides are correlated or complementary. This raises a logical problem: once two principles have been distinguished, one must explain how they relate. Much later thought has tried to refute or avoid dualism. Augustine, a former Manichaean, argued that evil is a privation of good rather than a positive principle, while Thomas Aquinas stressed the role of matter in human nature and knowledge.

Today dualism remains alive in debates about consciousness, ethics and theology, although in the philosophy of mind materialist monism gained ground during the twentieth century.