plural noun
Groups of connected ideas that explain how or why something happens, especially in science.
These theories explain how stars are formed.
Scientists compare theories with evidence.
American English
How to pronounce theories
nounB2Very common word
THEEreez
/ˈθi.ɹiz/
2 syllables · Stress the first syllable.
Form of theory
Groups of connected ideas that explain how or why something happens, especially in science.
What to listen for
“Theories” is commonly pronounced with three syllables (/ˈθi.ɚ.iz/) or with a shorter two-syllable form (/ˈθi.ɹiz/). Both are common in American English.
Three-syllable form/ˈθi.ɚ.iz/
Shorter two-syllable form/ˈθi.ɹiz/
Also heard/ˈθi.ɹiz/
Meanings & examples
plural noun
Explanations that people suggest for events or situations but that have not been proved.
Several theories about the accident are being investigated.
Her theories about the missing money changed over time.
plural noun
The ideas and rules of a subject, studied as knowledge rather than as practical work.
Different theories of learning are taught in the course.
These theories are useful, but practice is also important.
Useful expressions
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.
Related words & forms
The plural is theories, not theorys.