1the division of something conceptually into two opposed or contrasted aspects, or the state of being so divided:a dualism between man and nature Philosophy a theory or system of thought that regards a domain of reality in terms of two independent principles, especially mind and matter ( Cartesian dualism). Compare with idealism, materialism, and monism. the religious doctrine that the universe contains opposed powers of good and evil, especially seen as balanced equals. in Christian theology, the heresy that in the incarnate Christ there were two coexisting persons, human and divine. 2the quality or condition of being dual; duality.