Principal vs Principle: How to Tell Them Apart
Principal means main, or names a head of school. A principle is a rule or belief.
The principal reason. A matter of principle.
The test that settles it
The principal is your pal — and that is also the spelling for the main one.
“the ___ cause” → the main one, so principal.
“moral ___” → beliefs, so principles.
Only principle is exclusively a noun. If the word is describing something, it is principal.
Principal: main, or a head
An adjective meaning chief or most important. As a noun it means the head of a school or college, a lead performer, or the original sum of a loan.
The principal objection is cost.
She was appointed principal.
Interest is charged on the principal.
Swap in main. If it works, principal.
Principle: a rule or belief
A noun only. A fundamental truth, a rule of conduct, or a scientific law. It cannot describe anything.
The principle of equal treatment.
He resigned on a principle.
The principles of thermodynamics.
Swap in rule. If it works, principle.
Side by side
| Principal | Principle |
|---|---|
| Main, or a head | A rule or belief |
| Adjective and noun | Noun only |
| Ends -pal | Ends -ple, like rule |
| The principal issue | A matter of principle |
The exceptions
The phrase meaning in theory takes the rule word: we agree in principle. There is no such phrase as in principal.
The original amount of a debt, as opposed to the interest on it, is the principal — because it is the main sum.
Where people get it wrong
| Incorrect | Correct | Why |
|---|---|---|
| a man of high principals | a man of high principles | Beliefs. |
| the principle reason | the principal reason | The main one. |
| We agree in principal. | We agree in principle. | In theory. |
| She met the school principle. | She met the school principal. | The person. |
Practice — choose the right word, then check yourself.
- Cost was the ___ factor.
- It goes against my ___.
- The ___ addressed the assembly.
- They accepted the plan in ___.
- Repayments reduce the ___.
Show the answers
1. principal 2. principles 3. principal 4. principle 5. principal
Frequently asked
What is the quickest test?
Ask whether the word is describing a noun. If it is, only principal can do that job.
Is principled a word?
Yes — and it is built on the rule word: a principled objection means one grounded in belief.
More words people confuse
