hypothesis
noun
Christian ThorsbergStephanie WeaverArthur Conan Doyle
Usage of Theory and Hypothesis
While hypothesis and theory are both commonly used in non-technical contexts to mean "idea" or "hunch," the words function differently in the sciences. Hypothesis technically refers to an assumption that is proposed expressly so that it can be tested to see if it might be true. Theory refers to a principle that has been formed as an attempt to explain things that have already been substantiated by data; because of the rigors of experimentation and control, a theory is understood to be much more likely to be true than a hypothesis is, and is in fact relied upon for further scientific investigations. For this reason, it is an error to assert that a scientific theory is nothing more than conjecture.
Did you know?
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
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., editors, 1999
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.
Mrigakshi Dixit, Interesting Engineering, 4 Nov. 2025
The idea is referred to as the dual-exposure hypothesis, and Hill noted that it’s supported by decades of research, including from the LEAP trial.
—Meg Tirrell, CNN Money, 3 Nov. 2025
Physicist Gabriele Greco got in on the debate with a hypothesis of his own.
—Regina G. Barber, NPR, 31 Oct. 2025
Capturing a moment under specific conditions can help validate a hypothesis or guide mission changes.
—Suzanne Wright, USA Today, 29 Oct. 2025
See All Example Sentences for hypothesis
Cite this Entry
“Hypothesis.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/hypothesis. Accessed 11 Nov. 2025.
Copy CitationKids Definition
hypothesis
noun
Medical Definition
hypothesis
noun
J. S. Mill
Share