# duality

/duˈæɫəti/ (US) · /djuːˈælɪti/ (UK) · CEFR C1 · Noun

Source: https://englishreference.com/word/duality
Updated: 2026-05-08

## Definition

the state of having two different parts or qualities that exist together. It often describes things that have two sides, like light and dark or good and evil.

For teachers: the state of having two distinct, often contrasting or complementary, parts or aspects. In scientific contexts, it refers to the property of a single entity behaving in two different ways depending on the observation.

## Examples

- The novel explores the duality of human nature.
- The architect's design emphasizes the duality of light and shadow to create a sense of depth.
- In quantum mechanics, wave-particle duality suggests that every particle or quantum entity may be described as either a particle or a wave depending on the experimental apparatus used.

## Usage notes

- Uncountable when referring to the abstract concept; countable when referring to specific instances or mathematical relationships.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.