American English
/ˈθi.ɹi/
2 syllables · Stress the first syllable.
A group of connected ideas that explains how or why something happens, especially in science.
“Theory” is often said in two syllables, “THEE-ree” (/ˈθiɹi/), but you may also hear three syllables, “THEE-uh-ree” (/ˈθiəɹi/).
A group of connected ideas that explains how or why something happens, especially in science.
This theory explains how diseases spread.
Scientists tested the theory with new data.
scientific theory · develop a theory · test a theory · the theory of evolution
a theory about + noun
the theory that + subject + verb
An explanation that someone suggests for an event or situation, but that has not been proved.
My theory is that the dog followed us home.
Her theory about the missing keys was correct.
In everyday English, theory can mean an idea that is not certain. In science, a theory can be strongly supported by evidence.
have a theory · a theory about what happened · a wild theory
have a theory about + noun
my theory is that + subject + verb
The ideas and rules of a subject, studied as knowledge rather than as practical work.
She studied music theory at college.
The course combines theory with practical training.
music theory · economic theory · theory and practice
study the theory of + noun
theory and practice
According to ideas or rules, but not necessarily in real life.
In theory, the plan should work.
An explanation used for now, even though it may change later.
Our working theory is that the leak started in the kitchen.
General ideas and their use in real situations.
The course connects theory and practice.
The plural is theories, not theorys.