From the Latin dualis meaning “containing two”; the belief that the universe has a double nature, and that therefore “the real” is either of two kinds of, or controlled by, two powers. The opposite of this, monism, from the Greek monos, “sole,” is the doctrine that everything is of the same fundamental kind. The term “dualism” has been applied to oppositions in many subjects, therefore the use here of the plural “dualisms.” In fact dualism can be said to be the dominant trope of Western culture.
Two ancient Greek philosophers, Parmenides and Heraclitus, were monists. Parmenides advanced a monism based on Being, describing motion of change as unreal, while Heraclitus advanced a monism based on Becoming, seeing nothing as static everything in flux and change as the eternal law of things. The teachings of these two philosophers are important because Plato (427-347 B.C.E.), in seeking to join the two together, produced his metaphysical dualism.