Theory | Definition of theory by Merriam-Webster

Full Definition of THEORY

1

: the analysis of a set of facts in their relation to one another

2

: abstract thought : speculation

3

: the general or abstract principles of a body of fact, a science, or an art <music theory>

4

a : a belief, policy, or procedure proposed or followed as the basis of action <her method is based on the theory that all children want to learn>

b : an ideal or hypothetical set of facts, principles, or circumstances —often used in the phrase in theory <in theory, we have always advocated freedom for all>

5

: a plausible or scientifically acceptable general principle or body of principles offered to explain phenomena <the wave theory of light>

6

a : a hypothesis assumed for the sake of argument or investigation

b : an unproved assumption : conjecture

c : a body of theorems presenting a concise systematic view of a subject <theory of equations>

See theory defined for English-language learners

See theory defined for kids

Examples of THEORY

The immune surveillance theory of cancer holds that in a way we all do have cancer, that a healthy immune system fights off rogue cells as they appear. —Sallie Tisdale, Harper's, June 2007
The family's theory was that the cheating businessmen somehow framed their brother. —Eliza Griswold, Harper's, September 2006
The theory of the teacher with all these immigrant kids was that if you spoke English loudly enough they would eventually understand. —E. L. Doctorow, Loon Lake, (1979) 1980
While strolling around, we kept the run of the moon all the time, and we still kept an eye on her after we got back to the hotel portico. I had a theory that the gravitation of refraction, being subsidiary to atmospheric compensation, the refrangibility of the earth's surface would emphasize this effect in regions where great mountain ranges occur, and possibly so even-handed impact the odic and idyllic forces together, the one upon the other, as to prevent the moon from rising higher than 12,200 feet above sea-level. This daring theory had been received with frantic scorn by some of my fellow-scientists, and with an eager silence by others. —Mark Twain, A Tramp Abroad, 1880
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Origin of THEORY

Late Latin theoria, from Greek theōria, from theōrein

First Known Use: 1592

Related to THEORY

Synonyms: hypothesis, proposition, supposition, thesis

Synonym Discussion of THEORY

hypothesis, theory, law mean a formula derived by inference from scientific data that explains a principle operating in nature. hypothesis implies insufficient evidence to provide more than a tentative explanation <a hypothesis explaining the extinction of the dinosaurs>. theory implies a greater range of evidence and greater likelihood of truth <the theory of evolution>. law implies a statement of order and relation in nature that has been found to be invariable under the same conditions <the law of gravitation>.

Definition of THEORY for Kids

1

: an idea or opinion that is presented as true <Nobody knows where he went, but each of us has a theory.> <Perhaps they were formulating their own theories about how Cedric had died. — J. K. Rowling, Goblet of Fire>

2

: a general rule offered to explain a scientific phenomenon <the theory of gravity>

3

: the general rules followed in a science or an art <music theory>

Medical Definition of THEORY

1

: the general or abstract principles of a body of fact, a science, or an art <the theory and practice of medicine>

2

: a plausible or scientifically acceptable general principle or body of principles offered to explain natural phenomena <a theory of organic evolution>—see atomic theory, cell theory, germ theory

3

: a working hypothesis that is considered probable based on experimental evidence or factual or conceptual analysis and is accepted as a basis for experimentation

—the·o·ret·i·cal \ˌthē-ə-ˈret-i-kəl, ˌthi(ə)r-ˈet-\ also the·o·ret·ic \-ik\ adjective

—the·o·ret·i·cal·ly \-i-k(ə-)lē\ adverb

Learn More About THEORY

Thesaurus: All synonyms and antonyms for "theory"

Spanish Central: Spanish translation of "theory"

Nglish: Translation of "theory" for Spanish speakers

Britannica English: Translation of "theory" for Arabic speakers

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