Longman Dictionary of Contemporary English homepage


Date: 1500-1600
Language: Late Latin
Origin: theoria, from Greek, from theorein 'to look at'


theo‧ry S2 W1 plural theories
1 [countable]HP an idea or set of ideas that is intended to explain something about life or the world, especially an idea that has not yet been proved to be true [↪ theoretical]
theory about/on
different theories about how the brain works
theory of
Darwin's theory of evolution
theory that
the theory that light is made up of waves
2 [uncountable]H general principles and ideas about a subject:
Freudian theory has had a great influence on psychology.
political/economic/literary etc theory
I'm taking a course on political theory.

in theory

something that is true in theory is supposed to be true, but might not really be true or might not be what will really happen:
In theory, everyone will have to pay the new tax.
4 [countable] an idea or opinion that someone thinks is true but for which they have no proof
theory that
Detectives are working on a theory that he knew his murderer.
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