being twofold; a classification into two opposed parts or subclasses; the dichotomy between eastern and western culture

[ Syn: dichotomy ]

(physics) the property of matter and electromagnetic radiation that is characterized by the fact that some properties can be explained best by wave theory and others by particle theory

[ Syn: wave-particle duality ]

(geometry) the interchangeability of the roles of points and planes in the theorems of projective geometry