theory
Pluraltheories
- 1An idea that explains why something happens or how something works, often one that has not been proved.
Like a guess you make before you know the real answer.
I have a theory about why the cat keeps hiding under the bed.
My theory is that he simply forgot about the meeting.
UsageSay I have a theory that... or a theory about something.
Similarhypothesis, idea, notion, explanation, guess
- 2A well-tested explanation that fits the known facts and correctly predicts new ones.
Like a map that has been checked so many times you trust it to guide you somewhere new.
Scientists accepted the theory after many experiments supported it.
A good theory can predict things we have not seen yet.
Similarexplanation, model
Note
- 3The ideas, rules, and methods behind a subject, skill, or game, rather than actually doing it.
Like learning the rules of a game before you actually play it.
She knows the theory of music but rarely plays an instrument.
Learning the theory comes before practicing the actual steps.
UsageSay music theory, or theory and practice.
Oppositepractice
Note
- 4A branch of study that tries to fully describe one kind of thing.
Like a whole subject built just to understand one type of thing.
Graph theory is the math of points joined by lines.
Mathematicians built a whole theory to explain these shapes.
UsageSay number theory, with no a or the.
Note
Less common meanings
- 5In logic, a set of basic rules and everything that can be proved from them.
Like a game where you set a few starting rules, then list everything those rules allow.
A theory in logic starts with a few rules we accept as true.
Mathematicians showed that the theory contained no contradictions.
Note
- 6The act of thinking deeply or reflecting on something.
Note
Practice
Can you tell the meanings of theory apart? Answer 3 quick questions from this page, or write your own sentence and AI will check it.
Origin
It comes from a Greek word meaning "contemplation" or "looking at" something, which passed through Latin and French into English.
Checked 1 Nov 2026 · 3 facts
- Theory ultimately comes from Ancient Greek θεωρία, meaning contemplation. fr.wiktionary.org
- The Greek source word also meant looking at something. en.wikipedia.org
- The word passed through Latin and French into English. en.wiktionary.org