duality

American  

[doo-al-i-tee, dyoo-] / duˈæl ɪ ti, dyu- /

noun

1. a dual state or quality.

2. Mathematics. a symmetry within a mathematical system such that a theorem remains valid if certain objects, relations, or operations are interchanged, as the interchange of points and lines in a plane in projective geometry.

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duality British  

/ djuːˈælɪtɪ /

noun

1. the state or quality of being two or in two parts; dichotomy

2. physics the principle that a wave-particle duality exists in microphysics in which wave theory and corpuscular theory are complementary. The propagation of electromagnetic radiation is analysed using wave theory but its interaction with matter is described in terms of photons. The condition of particles such as electrons, neutrons, and atoms is described in terms of de Broglie waves

3. geometry the interchangeability of the roles of the point and the plane in statements and theorems in projective geometry

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Other Word Forms

• nonduality noun

Etymology

Origin of duality

1350–1400; Middle English dualitie < Late Latin duālitās. See dual, -ity

Explanation

As hinted at by the word "dual" within it, duality refers to having two parts, often with opposite meanings, like the duality of good and evil. If there are two sides to a coin, metaphorically speaking, there's a duality. Peace and war, love and hate, up and down, and black and white are dualities. Another term for a duality is a dichotomy. Duality has technical meanings in geometry and physics. In geometry, duality refers to how points and planes have interchangeable roles in projective geometry. In physics, duality is the property of matter and electromagnetic radiation to be understood best through wave theory or particle theory.

Example Sentences

Despite the uncertainty about its interpretation, wave-particle duality lies at the core of quantum mechanics.

From Science Daily • Mar. 10, 2026

"I'm a person of cultural duality," he told Associated Press.

From BBC • Feb. 14, 2026

It addresses issues of duality and the uncertainty of her standing in society as both a woman and an immigrant.

From Los Angeles Times • Feb. 9, 2026

Halloween, for all its associations with extremes of terror, is also bound up in the cozy innocence of childhood memories, and to my mind, few movies fit that duality better than “The Fog.”

From The Wall Street Journal • Oct. 29, 2025

In fact, they had encountered the same wave-particle duality of light that was confounding their elders in physics.

From "Big Science" by Michael Hiltzik

Related Words

• artifice
• chicanery
• deceit
• dishonesty
• falsehood
• hypocrisy