state of being dual or twofold; a twofold division; any system which is founded on a double principle, or a twofold distinction-a view of man as constituted of two original and independent elements, as matter and spirit.-a system which accepts two gods, or two original principles, one good and the other evil.-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.-the theory that each cerebral hemisphere acts independently of the other.