Definition of theory
1 : a plausible or scientifically acceptable general principle or body of principles offered to explain phenomena the wave theory of light
2a : 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 learnb : 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
4 : the general or abstract principles of a body of fact, a science, or an art music theory
5 : abstract thought : speculation
6 : the analysis of a set of facts in their relation to one another
Examples of theory in a Sentence
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
a widely accepted scientific theory
Her method is based on the theory that all children want to learn.
There are a number of different theories about the cause of the disease.
She proposed a theory of her own.
Investigators rejected the theory that the death was accidental.
There is no evidence to support such a theory.
He is a specialist in film theory and criticism.
Recent Examples of theory from the Web
One popular theory holds that using turn signals is a sign of weakness.
According to Trump’s budget proposal, the funding would come from $200 billion in tax breaks over nine years that would then — in theory — leverage $1 trillion worth of construction.
At the onset of a recovery, builders target high-end home buyers, who are less likely to be constrained by poor credit, according to a theory advanced by Robert Dietz, chief economist at the National Association of Home Builders.
The theory was that boomers who had spent their productive years investing for retirement would now be liquidating their stock holdings either to live on or to protect their next eggs by shifting into bonds.
Laland is a high-profile advocate for the idea of niche construction, a term from evolutionary theory that encompasses burrows, beaver dams and nests of birds and termites.
McEnermy, the chairman of the airport authority, said Wilson's foray into airport authority dealings had a hint of conspiracy theory to it.
Similar rock formations on other continents in the Southern Hemisphere helped strengthen early theories of continental drift.
Conspiracy theories bubble up on sites like 4chan and Reddit suggesting that the DNC killed Rich.
These example sentences are selected automatically from various online news sources to reflect current usage of the word 'theory'. Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.
Two related, yet distinct, meanings of theory
There are many shades of meaning to the word theory. Most of these are used without difficulty, and we understand, based on the context in which they are found, what the intended meaning is. For instance, when we speak of music theory we understand it to be in reference to the underlying principles of the composition of music, and not in reference to some speculation about those principles.
However, there are two senses of theory which are sometimes troublesome. These are the senses which are defined as “a plausible or scientifically acceptable general principle or body of principles offered to explain phenomena” and “an unproven assumption; conjecture.” The second of these is occasionally misapplied in cases where the former is meant, as when a particular scientific theory is derided as "just a theory," implying that it is no more than speculation or conjecture. One may certainly disagree with scientists regarding their theories, but it is an inaccurate interpretation of language to regard their use of the word as implying a tentative hypothesis; the scientific use of theory is quite different than the speculative use of the word.
Origin and Etymology of theory
Late Latin theoria, from Greek theōria, from theōrein
First Known Use: 1592
Synonym Discussion of theory
THEORY Defined for English Language Learners
Definition of theory for English Language Learners
: an idea or set of ideas that is intended to explain facts or events
: an idea that is suggested or presented as possibly true but that is not known or proven to be true
: the general principles or ideas that relate to a particular subject
THEORY Defined for Kids
Definition of theory for Students
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
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
Seen and Heard
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