In philosophy, any pair of irreducible, mutually heterogeneous principles used to analyze the nature and origins of knowledge (epistemological dualism) or to explain all of reality or some broad aspect of it (metaphysical dualism); also, any theory that employs dualisms.
Examples of epistemological dualisms are subject and object and sensation and sensibilia; examples of metaphysical dualisms are mind and matter, good and evil, and God and world. Dualism is distinguished from monism and pluralism .