Meaning of THEORY in English

theo ‧ ry S2 W1 AC /ˈθɪəri $ ˈθiːəri/ BrE AmE noun ( plural theories )

[ Word Family: noun : ↑ theorist , ↑ theory , ↑ theorem , theoretician; verb : ↑ theorize ; adverb : ↑ theoretically ; adjective : ↑ theoretical ]

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

1 . [countable] 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] 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.

3 . 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 OPP in practice :

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.

• • •


■ verbs

▪ come up with/develop a theory

These birds helped Darwin develop his theory of natural selection.

▪ test a theory

Researchers gave workers a questionnaire to test that theory.

▪ prove a theory

No evidence emerged to prove either theory.

▪ support a theory

Modern research strongly supports this theory.

▪ disprove a theory ( also refute a theory formal ) (=show that it is wrong)

Later experiments seemed to disprove the theory.

▪ discredit a theory (=make people stop believing in it)

These latest findings discredit his entire theory.


▪ a scientific theory

Scientific theories can be tested experimentally.

▪ an economic theory

His economic theory assumes that both labour and capital are perfectly mobile.

▪ a conspiracy theory (=a theory that an event was the result of secret plan made by two or more people)

A variety of conspiracy theories question the official account of President Kennedy’s assassination.

▪ a pet theory (=a personal theory that you strongly believe)

Each of them had his pet theory on what had caused the uprising.

■ phrases

▪ the theory of evolution/relativity etc

According to the theory of relativity, nothing can travel faster than light.

Longman Dictionary of Contemporary English.      Longman - Словарь современного английского языка.