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

Example Sentences

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 Yet Treasury Secretary Janet Yellen is turning this bedrock principle on its head by writing a global tax code with the help of European bureaucrats that would redound to the benefit of Beijing. Aharon Friedman, WSJ, 8 Mar. 2023 And if Putin is allowed to establish this principle, then Xi Jinping is observing this and will be encouraged. CBS News, 1 Mar. 2023 Good leaders don't let their teams forget this simple principle. Expert Panel®, Forbes, 6 Feb. 2023 Vladimir Putin has violated this principle more than any leader alive today. Matthew Continetti, National Review, 24 Dec. 2022 Does this information preservation principle imply that all information was already in existence in the big bang singularity? Scientific American, 12 Dec. 2022 But the trouble was how far ChatGPT insisted on extending this noncomparison principle. Jacob Stern, The Atlantic, 8 Dec. 2022 But the other principle, which Kagan presents as a necessary corollary, routinely corrupts the first with its aggrandizing nationalism and violent warmongering. Samuel Moyn, The New Republic, 14 Feb. 2023 Telegram and its cofounder and CEO, Pavel Durov, have built the platform’s reputation on one core principle: untrammeled free speech. Vivienne Walt, Fortune, 31 Jan. 2023 See More

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

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 22 Mar. 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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