hy·​poth·​e·​sis hī-ˈpä-thə-səs How to pronounce hypothesis (audio)
plural hypotheses hī-ˈpä-thə-ˌsēz How to pronounce hypothesis (audio)
: an assumption or concession made for the sake of argument
: an interpretation of a practical situation or condition taken as the ground for action
: a tentative assumption made in order to draw out and test its logical or empirical consequences
: the antecedent clause of a conditional statement

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The Difference Between Hypothesis and Theory

A hypothesis is an assumption, an idea that is proposed for the sake of argument so that it can be tested to see if it might be true.

In the scientific method, the hypothesis is constructed before any applicable research has been done, apart from a basic background review. You ask a question, read up on what has been studied before, and then form a hypothesis.

A hypothesis is usually tentative; it's an assumption or suggestion made strictly for the objective of being tested.

A theory, in contrast, is a principle that has been formed as an attempt to explain things that have already been substantiated by data. It is used in the names of a number of principles accepted in the scientific community, such as the Big Bang Theory. Because of the rigors of experimentation and control, it is understood to be more likely to be true than a hypothesis is.

In non-scientific use, however, hypothesis and theory are often used interchangeably to mean simply an idea, speculation, or hunch, with theory being the more common choice.

Since this casual use does away with the distinctions upheld by the scientific community, hypothesis and theory are prone to being wrongly interpreted even when they are encountered in scientific contexts—or at least, contexts that allude to scientific study without making the critical distinction that scientists employ when weighing hypotheses and theories.

The most common occurrence is when theory is interpreted—and sometimes even gleefully seized upon—to mean something having less truth value than other scientific principles. (The word law applies to principles so firmly established that they are almost never questioned, such as the law of gravity.)

This mistake is one of projection: since we use theory in general to mean something lightly speculated, then it's implied that scientists must be talking about the same level of uncertainty when they use theory to refer to their well-tested and reasoned principles.

The distinction has come to the forefront particularly on occasions when the content of science curricula in schools has been challenged—notably, when a school board in Georgia put stickers on textbooks stating that evolution was "a theory, not a fact, regarding the origin of living things." As Kenneth R. Miller, a cell biologist at Brown University, has said, a theory "doesn’t mean a hunch or a guess. A theory is a system of explanations that ties together a whole bunch of facts. It not only explains those facts, but predicts what you ought to find from other observations and experiments.”

While theories are never completely infallible, they form the basis of scientific reasoning because, as Miller said "to the best of our ability, we’ve tested them, and they’ve held up."

Choose the Right Synonym for hypothesis

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

Examples of hypothesis in a Sentence

In contrast to Bingham's hypothesis that Machu Picchu was the birthplace of the first Inca and the hearth area of the Inca civilization, current scholars believe that the city was built as a country estate … Roger Balm, Focus On Geography, Spring 2004
Campus veterans marvel at all the poolside apartments that have sprung up since Georgia popped the income cap off its merit awards. Professors are testing their hypothesis that instead of increasing college enrollment, the state's $1.7 billion scholarship program has been a blessing for the automobile industry—since so many families roll the savings into buying new cars. Greg Winter, New York Times, 31 Oct. 2002
Isaac Newton initially argued against a parabolic orbit for the … comet of 1680, preferring the hypothesis of two independent comets, one for the inbound and one for the outbound leg. However, Newton later showed that the orbit of the comet could indeed be fit by a parabola. Daniel C. Boice and Walter Huebner, "Physics and Chemistry of Comets," in Encyclopedia of the Solar System Paul R. Weissman et al., editors1999
As stated, our working hypothesis suggests a straightforward way to look for evidence that would confirm or disconfirm it: can you predict what is omitted and what is included in alphabetic representations? Timothy Shopen and Joseph M. Williams, Standards and Dialects in English, 1980
Other chemists rejected his hypothesis. Their hypothesis is that watching excessive amounts of television reduces a person's ability to concentrate. The results of the experiment did not support his hypothesis.
Recent Examples on the Web In the new study, published Monday in the journal Nature Human Behaviour, researchers examined each of these critiques and found support for the endurance pursuit hypothesis. Will Sullivan, Smithsonian Magazine, 14 May 2024 Advertisement Various scenarios for the odd cemetery have been proposed, including one hypothesis that the bones belong to a group of passing pilgrims killed by giant hailstones during a storm in the ninth century. San Diego Union-Tribune, 7 May 2024 See all Example Sentences for hypothesis 

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'hypothesis.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


Greek, from hypotithenai to put under, suppose, from hypo- + tithenai to put — more at do

First Known Use

1641, in the meaning defined at sense 1a

Time Traveler
The first known use of hypothesis was in 1641

Dictionary Entries Near hypothesis

Cite this Entry

“Hypothesis.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/hypothesis. Accessed 27 May. 2024.

Kids Definition


hy·​poth·​e·​sis hī-ˈpäth-ə-səs How to pronounce hypothesis (audio)
plural hypotheses -ə-ˌsēz How to pronounce hypothesis (audio)
: something not proved but assumed to be true for purposes of argument or further study or investigation

Medical Definition


hy·​poth·​e·​sis hī-ˈpäth-ə-səs How to pronounce hypothesis (audio)
plural hypotheses -ˌsēz How to pronounce hypothesis (audio)
: a proposition tentatively assumed in order to draw out its logical or empirical consequences and test its consistency with facts that are known or may be determined
it appears, then, to be a condition of the most genuinely scientific hypothesis that it be … of such a nature as to be either proved or disproved by comparison with observed factsJ. S. Mill

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