“Principal” and “principle” sound exactly the same, but they mean very different things. “Principal” usually refers to the head of a school, or to something that is the most important or main, while “principle” is a rule, belief, or basic truth. A quick shortcut: the principal is your pal, and a principle is a rule. Mix-ups between homophones like these are hard to spot because both words are spelled correctly, which is exactly the kind of slip TypoGuard is built to catch in context.
What “Principal” Means
“Principal” can be a noun or an adjective, and it has several related meanings:
- The head of a school: “The principal welcomed the new students.”
- Main or most important (adjective): “Cost was the principal reason for the delay.”
- The original amount of money in a loan or investment: “Your payment covers both principal and interest.”
- A leading performer or key person: “She is a principal dancer with the company.”
What “Principle” Means
“Principle” is only ever a noun. It means a rule, a basic truth, or a standard of behavior:
- “Honesty is a core principle of good business.”
- “He refused to lie on principle.”
- “The principle of gravity explains why objects fall.”
An Easy Memory Trick
There are two simple ways to remember the difference. First, the principal is your pal: the head of a school is a person, and “principal” contains the word “pal.” Second, “principle” ends in “-le,” just like “rule,” and a principle is a kind of rule.
Principal in Money Matters
In finance, “principal” always means the original sum of money, before interest is added. If you borrow 10,000 dollars, the principal is 10,000 dollars, and the interest is the extra cost of borrowing it. “Principle” never refers to money, so a sentence about loans, mortgages, or savings should always use “principal.”
Common Phrases to Know
- in principle (in theory, or in general agreement)
- on principle (because of a firm belief)
- as a matter of principle
- guiding principles
- principal reason
- principal investigator
- principal photography
- principal and interest
Learn More From a University Source
If you want a second opinion, Washington State University’s Common Errors in English Usage includes a helpful entry on principal and principle. It describes “principal” as a noun and adjective for someone or something highest in rank or importance, which matches the school and “main reason” uses above.
Examples in Context
- Correct: “The principal announced a new schedule.”
- Incorrect: “The principle announced a new schedule.”
- Correct: “It’s a matter of principle for me.”
- Incorrect: “It’s a matter of principal for me.”
- Correct: “The principal reason for the change was safety.”
Frequently Asked Questions
Is it “principal” or “principle” for the head of a school? It is always “principal.”
Is “principle” ever an adjective? No. “Principle” is only a noun. If you need an adjective meaning “main,” use “principal.”
What does “in principle” mean? It means in theory or in general agreement, even if the details still need to be worked out.
What is the plural of each word? “Principals” and “principles.”
Homophone Mix-Ups That Spellcheck Misses
Because “principal” and “principle” are both real words, a basic spellchecker will never flag the wrong one. A grammar checker Chrome extension like TypoGuard’s free grammar checker reads the sentence in context and catches homophone mistakes like this in real time, before your email, essay, or report goes out.
Want to catch these mix-ups automatically? Install TypoGuard for free and write with confidence.
