Dualism

 du·al·ism - noun
noun: dualism; plural noun: dualisms

1. the 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).
noun: Cartesian dualism - 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.

2. the quality or condition of being dual; duality.