What does complementarity mean?
Complementarity names the condition in which two things that are distinctly different nevertheless complete one another, each supplying precisely what the other lacks. It is most familiar as a general term for well-matched pairings — complementary skills in a team, complementary roles in a partnership — where difference is not an obstacle but the very source of strength. The word also has weightier technical lives: in physics, Niels Bohr's principle of complementarity holds that phenomena like light require mutually exclusive descriptions, as wave or particle, neither alone sufficient for a full picture; in molecular biology, it describes the base-pairing that gives DNA its double-stranded structure. Derived from the Latin 'complementum' via 'complementary', the noun carries formal, intellectual connotations and appears chiefly in academic and professional writing. Its enduring appeal lies in a quietly optimistic idea: that wholeness often comes not from sameness but from difference rightly joined.
nounThe state or principle of two things being different but mutually completing each other, so that together they form a whole or supply what the other lacks.
- A relationship in which two distinct things differ but each supplies what the other lacks, forming a functional whole (e.g. skills, roles, partners).
- In physics: Niels Bohr's principle that objects such as light or electrons have mutually exclusive properties (wave-like and particle-like) that must be described by separate, incompatible experimental frameworks, both being necessary for a complete account.
- In genetics/biochemistry: the specific pairing relationship between structures, such as complementary bases in DNA (A with T, C with G).
"Their partnership worked because of a genuine complementarity: she brought technical rigour, he brought commercial instinct."
"The success of the venture rested on the complementarity of its two founders' skills."
"Bohr's principle of complementarity holds that light behaves as either a wave or a particle depending on how it is observed."
The plural is rare and mainly found in academic writing discussing multiple instances of complementary relationships across contexts.
"The study compared the complementarities between trade partners across several regions."
Physicist Niels Bohr argued that light is both a wave and a particle — two contradictory pictures that can never be seen at once, yet are both needed to describe reality. He called this 'complementarity', and it reshaped how science thinks about truth itself.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of complementarity
Complementarity derives from the Latin 'complementum', meaning 'that which completes or fills up', itself from 'complere' ('to fill up, complete'). English first adopted the related adjective 'complementary' in the seventeenth century, and the abstract noun 'complementarity' emerged later, gaining particular prominence in the twentieth century through Niels Bohr's quantum-mechanical principle. It shares its root with 'complete', 'completion', and 'complement'.
Related word forms
How complementarity is actually used
A formal, largely academic word, common in scientific, philosophical, and sociological writing; rare in casual conversation. In physics it carries a precise technical meaning tied to Bohr's interpretation of quantum mechanics, which should not be conflated with the everyday sense of things 'fitting well together'.
Easily confused with complementarity
"Complimentary" means expressing praise or given free of charge, while "complementary" means completing or combining well with something else.