Definition of principle in English:


Line breaks: prin|ciple
Pronunciation: /ˈprɪnsɪp(ə)l


  • 1A fundamental truth or proposition that serves as the foundation for a system of belief or behaviour or for a chain of reasoning: the basic principles of justice
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    • And yet, of course, our principles of fairness and justice must be upheld.
    • Although its application was inevitably uneven, the Code Napoléon was intended to serve as a universal set of principles founded on reason.
    • Following the enlightenment principle of truth through reason alone, it was thought that history cannot be determined until theology has been removed.
    truth, proposition, concept, idea, theory, postulate; assumption, basis, fundamental, essence, essential; philosophy
  • 1.1 (usually principles) A rule or belief governing one’s behaviour: struggling to be true to their own principles [mass noun]: she resigned over a matter of principle
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    • If you can forsake your fundamental principles for any reason then you are not the kind of person who can take the country forward.
    • Rarely have I encountered anyone as passionate and determined in his principles as Donald Bruce, a true patriot and a man who led a remarkable life.
    • There are three key defining experiences in my life that form the foundation of my principles and beliefs.
  • 1.2 [mass noun] Morally correct behaviour and attitudes: a man of principle
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    • It seems that in situations such as this, politics become incompatible with conscience, principle, decency and self-respect.
    • How in one walk of life a person can have such a rigid sense of right and wrong - and in another he can operate with a total disregard for principle, integrity and fair play.
    • But he's clearly a man of principle and unbending honesty - who, at times, can be cruelly insensitive, as when he tells a man he has casually examined that he has a tumour.
  • 2A general scientific theorem or law that has numerous special applications across a wide field.
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    • Physics has a big advantage here, since the ability to derive interesting conclusions from general principles comes earlier in physics than in other sciences.
    • Guitar pickups work by the principles of magnetic induction.
    • One line of evidence for the holographic principle comes from black hole physics.
  • 2.1A natural law forming the basis for the construction or working of a machine: these machines all operate on the same general principle
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    • Yet, that was the age of levers and pulleys, and machines based on mechanical principles were being used as analog computers in many different ways.
    • The principles underlying steam power, machine tools, and mass production were less familiar, hence less transparent.
    • However, back then, explanations that were given to the general public regarding the actual principle of the flying machine appeared to be quite vague.
  • 3A fundamental source or basis of something: the first principle of all things was water
  • 3.1A fundamental quality determining the nature of something: the combination of male and female principles
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    • Just as the male and female principles complement each other, our views of history also much combine to give a holistic view of the past.
    • As sun and moon represent the male and female principles, once again we see the potential for a happy union between you.
    • Holding the rapt attention of the audience, the duo exemplified the concept of the male and female principles working in harmony and balance in the Universe, unique to Hindu mythology.
  • 3.2 [with adjective] Chemistry An active or characteristic constituent of a substance, obtained by simple analysis or separation: the active principle of Spanish fly
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    • Various studies on the active principles of the manchineel tree have shown tigliane phorbol esters to be the likely cause of the severe reactions.
    • The pungency of pepper is due to the active principles it contains - the volatile oil, piperine, and resin.
    • The active principles were identified as baicalein from the first and methyl gallate from the last two plants.


in principle

As a general idea or plan, although the details are not yet established: the government agreed in principle to a peace plan that included a ceasefire
More example sentences
  • The plan was accepted in principle but the details for it were not.
  • Councillors agreed to the scheme in principle, with the detail being delegated to planning officers.
  • The town council says it supports the plan in principle, but says there could be problems finding a suitable location.
Used to indicate that although something is theoretically possible, in reality it may not actually happen: in principle, the banks are entitled to withdraw these loans when necessary
More example sentences
  • The first test here should be whether infinite computing power is, in principle, even possible.
  • Although having a smoke free environment seems good in principle, how would it be enforced?
  • However, he sees no reason to believe that a machine cannot, in principle, do the things humans can do.
in theory, theoretically, on paper, in an ideal world; French en principe

on principle

Because of or in order to demonstrate one’s adherence to a particular belief: he refused, on principle, to pay the fine
More example sentences
  • I have never been in a limo in my life and would refuse to do so on principle.
  • Pittman said he later spoke to an employee who apologized and asked him to keep his subscription, but he quit on principle.
  • But I wouldn't go in there now on principle, even if you paid me.


late Middle English: from Old French, from Latin principium 'source', principia (plural) 'foundations', from princeps, princip- 'first, chief'.


The words principle and principal are pronounced in the same way but they do not have the same meaning. Principle is normally used as a noun meaning ‘a fundamental basis of a system of thought or belief’, as in this is one of the basic principles of democracy . Principal, on the other hand, is normally an adjective meaning ‘main or most important’, as in one of the country’s principal cities . Principal can also be a noun, where it is used to refer to the most senior or most important person in an organization or other group: the deputy principal .

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