Dualism: doctrine according to which the world consists of, or is explicable in terms of, two fundamental substances.

A central and controversial doctrine in philosophy in which reality is conceived as divided into two unbridgeable and incommensurable orders of being – primarily, mind and body, res cogitans and res extensa, the dualism instituted in modern Western philosophy by Descartes. Related forms of dualism have been perpetual in philosophy since the ancients – spirit-matter, man-nature, temporal-eternal, appearance-reality, subjective-objective and reason-emotion.

Source: What is Good? What is Bad? The Value of All Values across Time, Place and Theories’ by John McMurtry, Philosophy and World Problems, Volume I-III, UNESCO in partnership with Encyclopedia of Life Support Systems: Oxford, 2004-11.