What Does "Principal" Mean?
Principal functions as both an adjective and a noun.
As an adjective, it means "main," "chief," or "most important":
- The principal reason for the delay was a supply chain disruption.
- Her principal concern was the accuracy of the data.
- The principal argument in the report was never fully supported.
- Cost is the principal factor in the decision.
As a noun, it refers to a person in a leading role, or to the main sum of money (in finance):
- The school principal addressed the students at assembly. (head of a school)
- The principals of the firm signed the merger agreement. (leading members)
- Each principal in the negotiation had distinct objectives. (primary party)
- The loan's principal is $150,000; interest is charged on top. (original capital sum)
- She was a principal in the dance company. (leading performer)
What Does "Principle" Mean?
Principle is always a noun. It means a fundamental rule, belief, law, or standard that governs behavior or reasoning.
- The proposal violates a basic principle of fairness.
- He refused to sign on principle. (because of his values)
- The experiment is based on the principle of conservation of energy.
- Good design follows the principle that form should follow function.
- She is a person of strong principles. (moral standards)
- The principles outlined in the agreement must be honored. (foundational rules)
Principle is never an adjective and never refers to a person. If the word could be replaced by "rule," "belief," or "standard," use principle.
Side-by-Side Comparison
| Word | Part of Speech | Meaning |
|---|---|---|
| principal | Adjective, Noun | Main, chief; a leading person; the original capital sum |
| principle | Noun only | A rule, belief, standard, or law |
Memory Tricks
Two approaches work well for keeping these straight:
- A principAL is your pAL. (The school principal is your pal — both end in -al.)
- A principLE is a ruLE. (Both principle and rule end in -le.)
Common Errors
| Incorrect | Correct | Why |
|---|---|---|
| The principle cause of the error was a miscalculation. | The principal cause of the error was a miscalculation. | "Main cause" — needs the adjective principal. |
| She acted on her principals. | She acted on her principles. | Moral standards are principles, not principals. |
| The principal of supply and demand governs pricing. | The principle of supply and demand governs pricing. | An economic rule is a principle. |
| The principle stakeholders in the deal are… | The principal stakeholders in the deal are… | "Main stakeholders" — adjective use requires principal. |
Both Words in the Same Sentence
Because the two words are distinct, they can appear together without contradiction:
- The principal insisted that all students act on the school's core principles.
- The principal investor refused to proceed, citing a principle of ethical sourcing.
"In Principle" and Related Phrases
In principle is a fixed phrase meaning "in theory" or "as a general rule, though the details may differ": The board agreed in principle to the proposal. This phrase always uses principle. Similarly, on principle means "because of a moral stance": He refused on principle.
There is no phrase in principal in standard English usage.
"Principal" in Finance and Law
In financial and legal contexts, principal has specific technical meanings:
- In a loan: the original amount borrowed, separate from interest. After three years, the outstanding principal was $80,000.
- In a legal context: a person on whose behalf an agent acts. The agent cannot bind the principal without written authorization.
- In criminal law: a principal is a primary participant in a crime, as distinct from an accessory.
In all of these technical uses, principle would be wrong.
Frequently Asked Questions
Is "unprincipled" spelled correctly?
Yes. Unprincipled means lacking moral principles — it derives from principle (noun: moral rule) with the prefix un- and the suffix -d. Unprincipled behavior means behavior that violates ethical standards.
Can "principal" be used to mean "principle" in older texts?
In Early Modern English, the two spellings were less consistently differentiated. In contemporary standard English, they are treated as distinct words, and maintaining the distinction is expected in professional and academic writing.
Why do so many people mix up principal and principle?
Because they are homophones — they sound identical in speech. The difference only appears in writing, so readers who primarily consume audio content or type quickly by sound are more likely to conflate them. The "-al" / "-le" memory trick resolves the ambiguity for most contexts.