n. [ Cf. F. dualisme. ] State of being dual or twofold; a twofold division; any system which is founded on a double principle, or a twofold distinction; as: (a) (Philos.) A view of man as constituted of two original and independent elements, as matter and spirit. (Theol.) (b) A system which accepts two gods, or two original principles, one good and the other evil. (c) The doctrine that all mankind are divided by the arbitrary decree of God, and in his eternal foreknowledge, into two classes, the elect and the reprobate. (d) (Physiol.) The theory that each cerebral hemisphere acts independently of the other. [ 1913 Webster ]

An inevitable dualism bisects nature, so that each thing is a half, and suggests another thing to make it whole. Emerson. [ 1913 Webster ]