Principal vs. Principle | Definition & Examples

Principle and principal are pronounced the same but have different meanings.

  • Principal can be used as a noun to refer to a person in authority, the perpetrator of a crime, or the capital sum of a loan. It can also be used as an adjective to mean “most important” or “primary.”
  • Principle is a noun used to refer to a scientific, moral, or legal rule or standard.
Examples: Principal in a sentence Examples: Principle in a sentence
The principal of the school is very strict when it comes to attendance. Chris refused to pay the extra shipping costs on principle.
The principal finding of the study is questionable. Isaac Newton uncovered the principles of gravity and motion.

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Principal as a noun

Principal can be used as a noun to refer to a person in authority, especially in a school but also in other contexts such as businesses.

Examples: Principal to mean person in authority
After twenty years of being a teacher, Kelly became the school principal.

It can also refer to someone who is responsible for a crime.

Example: Principal to refer to a perpetrator of a crime
There was no evidence to suggest that the young man was a principal in the robbery.

Principal can also be used in financial contexts to refer to the capital sum of a loan.

Example: Principal to refer to a loan
Melissa was happy with the principal, but she wished the interest rate weren’t so high.

Principal as an adjective

Principal can be used as an adjective to mean “primary” or “most important.” It can also be used to refer to an original sum of money.

Examples: Principal as an adjective
The principal aim of the mission was to test Saturn’s atmosphere.

The principal amount was two thousand dollars.

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Principle is a noun

Principle is a noun used to refer to a legal, natural, or scientific rule or standard. It can also be used to refer to a general or personal moral standard.

Examples: Principle in a sentence
The principle of human rights is central to the idea of democracy.

As a matter of principle, the politician refused to accept campaign funding from big businesses.

Principle can only ever be used as a noun (the associated adjective is “principled,” meaning “based on principle”).

In principle or in principal

In principle is a common expression meaning “in theory.” It’s used to refer to a plan or idea, the details of which have not been established. “In principal” is never correct.

Examples: In principle in a sentence
Anna’s supervisor agreed in principle to the thesis topic, but they wanted to see a detailed plan before they officially agreed.

Worksheet: Principal vs. principle

You can test your understanding of the difference between “principle” and “principal” with the worksheet below. Fill in either “principle” or “principal” in each sentence.

  1. As he was responsible for the damage to the car, Hector said that he would pay for it out of _________.
  2. Because Dan was misbehaving, the teacher sent him to see the _________.
  3. Each week, June saved her wages and paid off a part of the _________.
  4. The _________ cause of the accident was that someone had spilled water on the floor.
  5. In _________, the investor agreed with the business idea.
  1. As he was responsible for the damage to the car, Hector said that he would pay for it out of principle.
    • “Principle” is a noun used to refer to a rule or standard. In this instance, “principle” is used to refer to a personal standard.
  1. Because Dan was misbehaving, the teacher sent him to see the principal.
    • “Principal” can be used as a noun to refer to a person of authority in a school or business.
  1. Each week, June saved her wages and paid off a part of the principal.
    • “Principal” is used here to refer to the capital sum of a loan.
  1. The principal cause of the accident was that someone had spilled water on the floor.
    • “Principal” can be used as an adjective to mean “primary” or “most important.”
  1. In principle, the investor agreed with the business idea.
    • Here, “principle” is used to complete the expression “in principle,” meaning “in theory.”

    Other interesting language articles

    If you want to know more about commonly confused words, definitions, and differences between US and UK spellings, make sure to check out some of our other language articles with explanations, examples, and quizzes.

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    Eoghan Ryan

    Eoghan has a lot of experience with theses and dissertations at bachelor's, MA, and PhD level. He has taught university English courses, helping students to improve their research and writing.