prin·​ci·​ple ˈprin(t)-s(ə-)pəl How to pronounce principle (audio)
: a comprehensive and fundamental law, doctrine, or assumption
: a rule or code of conduct
: habitual devotion to right principles
a man of principle
: the laws or facts of nature underlying the working of an artificial device
: a primary source : origin
: an underlying faculty or endowment
such principles of human nature as greed and curiosity
: an ingredient (such as a chemical) that exhibits or imparts a characteristic quality
capitalized Christian Science : a divine principle : god
Principle vs. Principal: Usage Guide

Evidence of confusion between principle and principal can be found even in publications overseen by professional editors. To keep these words straight, remember that principle functions only as a noun, and in its most common uses refers to a basic rule or law, as in

a guiding principle


a matter of principle.

If you are looking for an adjective form of this word, you must use principled, as in

taking a principled stand.

Principal functions as both a noun and an adjective. The noun has various meanings referring to someone with controlling authority

the school principal

or in a leading position

the ballet's two principals

, but also has meanings relating to finance, law, and architecture. As an adjective, principal typically means "most important," as in

the principal reason.

in principle
: with respect to fundamentals
prepared to accept the proposition in principle

Examples of principle in a Sentence

Urban guerrilla warfare was futile against a thermonuclear superstate that would stop at nothing to defend the profit principle. Philip Roth, American Pastoral, 1997
Better, of course, to take a higher road, operate on the principle of service and see if things don't turn out better … Richard Ford, Independence Day, 1995
Pointlessness was life's principle, and it spread its sadness. Arthur Miller, Timebends, 1987
His investment strategy is based on the principle that the stock market offers the best returns for long-term investors. the basic principles of hydraulics
Recent Examples on the Web Today, marked by the urgent need for global cooperation and solidarity, both at home and abroad, these principles are more crucial than ever to confront the formidable challenges of our time and usher in peace and prosperity for future generations. Michael Sheldrick, Forbes, 30 Nov. 2023 Numerous excerpts of the book, including in Fortune, have portrayed a climate where, for instance, former Attorney General James Comey would investigate, including through several mock trials, the violated principle of an employee not bringing in bagels as promised. Will Daniel, Fortune, 29 Nov. 2023 But the most current laws modeled after these ancient principles are often traced back to two famous names: Sierra Club founder John Muir and U.S. Forest Service founder Gifford Pinchot. John Muir was a naturalist and writer who cofounded the Sierra Club in his later years. Katie Hill, Outdoor Life, 29 Nov. 2023 This practice is based on a principle known as material reciprocity, which means that broadcast and performance revenues are only paid out to countries that apply the same rights. Richard Smirke, Billboard, 28 Nov. 2023 The education system stressed principles of antifascism. Rebecca Mead, The New Yorker, 27 Nov. 2023 Ruffini has long admired the principles of Japanese design, having also partnered with Hiroshi Fujiwara, Comme des Garçons and Junya Watanabe. Laura Hawkins, Vogue, 27 Nov. 2023 When simple imitation fell short, the stagers went deeper, explaining the principles behind Bausch’s movement style. Marina Harss, New York Times, 25 Nov. 2023 The working principle behind a thermoelectric generator is the Seebeck effect, which describes how a material develops a voltage difference in response to a temperature differential across it. Sid Assawaworrarit, IEEE Spectrum, 25 Nov. 2023 See More

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

Word History


Middle English, from Middle French principe, principle, from Old French, from Latin principium beginning, from princip-, princeps initiator — more at prince

First Known Use

14th century, in the meaning defined at sense 1a

Time Traveler
The first known use of principle was in the 14th century

Dictionary Entries Near principle

Cite this Entry

“Principle.” Dictionary, Merriam-Webster, Accessed 6 Dec. 2023.

Kids Definition


prin·​ci·​ple ˈprin(t)-s(ə-)pəl How to pronounce principle (audio)
: a general or basic truth on which other truths or theories can be based
scientific principles
: a rule of conduct
a person of high principles
: a law or fact of nature which makes possible the working of a machine or device
the principle of magnetism
the principle of the lever

Medical Definition


prin·​ci·​ple ˈprin(t)-sə-pəl How to pronounce principle (audio)
: a comprehensive and fundamental law, doctrine, or assumption
: an ingredient (as a chemical) that exhibits or imparts a characteristic quality
the active principle of a drug

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