duality

Noun

1. The quality of containing or comprising two often opposed parts or aspects.
   • He was fascinated by the duality of human nature.
   • the moral duality of certain characters
   • Mother Nature's eternal duality, both life-giving and destructive
2. The aggregate of two complementary subclasses or parts.
   • philosophical duality
   • The novel explored the duality of good and evil.
   • that fundamental duality that characterises the life of all animals—hungry or sated
3. The mathematical equivalence of two seemingly different theoretical descriptions of a physical system.
   • wave-particle duality
4. The interchangeability of points and planes.