State of being dual or twofold; a twofold division; any system which is founded on a double principle, or a twofold distinction
- The condition of being double; duality.
- Philosophy The view that the world consists of or is explicable as two fundamental entities, such as mind and matter.
- Psychology The view that the mind and body function separately, without interchange.
- Theology The concept that the world is ruled by the antagonistic forces of good and evil.
- Theology The concept that humans have two basic natures, the physical and the spiritual.