hy·​poth·​e·​sis | \ hī-ˈpä-thə-səs \
plural hypotheses\ hī-​ˈpä-​thə-​ˌsēz \

Definition of hypothesis

1a : an assumption or concession made for the sake of argument
b : an interpretation of a practical situation or condition taken as the ground for action
2 : a tentative assumption made in order to draw out and test its logical or empirical consequences
3 : the antecedent clause of a conditional statement

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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

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."

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.
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Recent Examples on the Web

Photo: Eric Staudenmaier Dover Street Market’s arrival in Los Angeles will test that hypothesis. Jacob Gallagher, WSJ, "Los Angeles Is a Fashion Wasteland. Can One Store Change That?," 5 Nov. 2018 Still, he and Britta Osthaus, a senior lecturer in the School of Psychology, Politics and Sociology at Canterbury Christ Church University in Britain, set out to test the hypothesis. Laura M. Holson, The Seattle Times, "Your Dog May Be Smart, but She’s Not Exceptional," 8 Oct. 2018 The original hypothesis of the series, which was initially commissioned by the BBC, was that class structure in the U.K. is so strong that a person’s life path would be set at birth. Vogue, "These Are the 66 Best Documentaries of All Time," 8 Aug. 2018 The principal hypothesis is that, for all of its horror, the experience of war can give soldiers a sense of purpose and community that is hard to find in contemporary civilian life. Martin Fritz Huber, Outside Online, "'Leave No Trace' Is Brutally Honest About Rewilding," 28 June 2018 The study was intended to test the hypothesis that one drink a day is better for one’s heart than none, among other benefits of moderate drinking. Roni Caryn Rabin, New York Times, "It Was Supposed to Be an Unbiased Study of Drinking. They Wanted to Call It ‘Cheers.’," 18 June 2018 With the fembot, the team can manipulate the visual signals the robot is giving to signal interest or non-interest, in order to test that hypothesis. Matt Simon, WIRED, "Why Scientists Turned This Taxidermy Bird Into a Robot," 1 June 2018 The collective-gravity hypothesis isn't a silver bullet, however. Nola Taylor Redd, Space.com, "No Need for Planet Nine? Small Objects' Gravity Could Explain Weird Orbits," 5 June 2018 Boland’s hypothesis is that the culprit in canines is exposure to outdoor air pollution — fine air particulates, including dust and pollen — early in a puppy’s development. Stacey Burling, Philly.com, "Penn study: Summer puppies more prone to heart disease," 21 May 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'hypothesis.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of hypothesis

1641, in the meaning defined at sense 1a

History and Etymology for hypothesis

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

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Last Updated

16 Jan 2019

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Time Traveler for hypothesis

The first known use of hypothesis was in 1641

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More Definitions for hypothesis



English Language Learners Definition of hypothesis

: an idea or theory that is not proven but that leads to further study or discussion


hy·​poth·​e·​sis | \ hī-ˈpä-thə-səs \
plural hypotheses\ -​ə-​ˌsēz \

Kids Definition of hypothesis

: something not proved but assumed to be true for purposes of argument or further study or investigation


hy·​poth·​e·​sis | \ hī-ˈpäth-ə-səs \
plural hypotheses\ -​ˌsēz \

Medical Definition of hypothesis

: 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 facts— J. S. Mill

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