Principal and principle end with different letters and do different jobs. Principal, with -al, means main or chief. It is also the noun for the head of a school and, in finance, for the original sum of a loan.
Principle, with -le, is always a noun. It means a rule, a belief or a basic law: a moral principle, the principle of gravity, in principle.
The classic memory line is "the principal is your pal". A principle is a rule, and both words stay in their places. This page gives the meanings, eight examples and 15 questions.
What each word means
principal
principal (adjective and noun): main, chief, the head of a school, or the original sum of a loan. "The principal reason." "The school principal."
principle
principle (noun): a rule, a belief or a basic law. "Honesty is a principle." "The principle of gravity."
The rule
Principal means main or first
- As an adjective: the principal reason, the principal entrance, the principal character.
- As a noun for a person: the principal of a school, or a business partner in a company.
- In finance: the principal is the original amount of a loan, before interest.
- It can also mean a leading performer in an orchestra or a play.
Principle is a rule
- A moral belief: "She has strong principles."
- A basic scientific or logical law: "the principle of gravity", "the principle of least effort".
- A rule for behaviour: "I refuse on principle."
- In principle means in theory or in general: "In principle, I agree."
The pal and rule test
- The principal is your pal: the head of the school, spelled with -al.
- A principle is a rule: both words end in -le, and a rule is not a person.
- Put the or an adjective in front of the word. A person or a main thing takes principal.
- If the word means a belief or a law, it is principle, and it never describes a noun as an adjective.
Traps in writing
- In principle, not in principal, means in theory.
- On principle, not on principal, means because of a belief.
- A man of principle has strong beliefs. A principal is a school head or a sum of money.
- Principal is both an adjective and a noun. Principle is only a noun, so it never stands before another noun.
How to remember
The trick: The principal is your pal (the head of the school). A principle is a rule. Principal can also mean main; principle never does.
Examples
- The principal reason for the delay was the weather.Principal is an adjective meaning main.
- The school principal spoke to the students.The head of a school is the principal, a person.
- Honesty is an important principle.Principle is a belief or rule, so the -le spelling is correct.
- In principle, I agree with the plan.In principle is a fixed phrase meaning in theory.
- She refused on principle.On principle means because of a belief.
- The principal amount of the loan is £10,000.In finance, the original sum is the principal.
- We learned the principle of gravity at school.A scientific law is a principle.
- The main and principal entrance is on the left.Principal is an adjective here, close in meaning to main.
Common mistakes
- Wrong: The school principle called my parents. Right: The school principal called my parents.
- The head of a school is the principal, a person, with -al.
- Wrong: He is a man of principal. Right: He is a man of principle.
- A belief or rule is a principle, with -le.
- Wrong: In principal, the idea is good. Right: In principle, the idea is good.
- In principle is the fixed phrase meaning in theory.
- Wrong: The principal of gravity is easy to see. Right: The principle of gravity is easy to see.
- A scientific law is a principle, not a main thing.
- Wrong: She stuck to her principals. Right: She stuck to her principles.
- Beliefs are principles, spelled with -le.
Practice drill
Answer all 15 questions. Each answer is marked at once, and the rule is explained under the question.
The ___ reason for the delay was the weather.
Show answer and explanation
Answer: A. principal The adjective meaning main is principal with -al.
The school ___ spoke to the students.
Show answer and explanation
Answer: B. principal The head of a school is the principal, a person.
Honesty is an important ___.
Show answer and explanation
Answer: C. principle A belief is a principle with -le.
In ___, I agree with the plan.
Show answer and explanation
Answer: D. principle In principle is the fixed phrase meaning in theory.
She refused on ___.
Show answer and explanation
Answer: A. principle On principle means because of a belief.
The ___ amount of the loan is £10,000.
Show answer and explanation
Answer: B. principal In finance, the original sum is the principal with -al.
We learned the ___ of gravity at school.
Show answer and explanation
Answer: C. principle A scientific law is a principle with -le.
The main and ___ entrance is on the left.
Show answer and explanation
Answer: D. principal Principal is the adjective meaning main.
He is a man of ___.
Show answer and explanation
Answer: A. principle A man of principle has strong beliefs.
The ___ character in the novel is a teacher.
Show answer and explanation
Answer: B. principal The main character is described with the adjective principal.
She would never lie, on ___.
Show answer and explanation
Answer: C. principle On principle shows the action follows a belief.
The meeting went ahead in ___ but not in detail.
Show answer and explanation
Answer: D. principle In principle means in general or in theory.
The bank asked for the ___ back.
Show answer and explanation
Answer: A. principal The original sum of a loan is the principal with -al.
His argument is based on a sound ___.
Show answer and explanation
Answer: B. principle A basic rule or law is a principle with -le.
The ___ dancers led the performance.
Show answer and explanation
Answer: C. principal The leading performers are the principals, with -al.
Questions learners ask
Is principal ever a noun for money?
Yes. In finance, the principal is the original amount borrowed, before interest is added. The word is a noun here, but it keeps the -al spelling because it means the main sum.
What does in principle mean?
In principle means in theory or in general, if the conditions are right: "In principle, we support the plan, but we need to see the cost." It does not mean the plan is certain to happen.
How can I remember the two spellings?
Use the pal line for the person: the principal is your pal. Use the rule line for the idea: a principle is a rule, and both words end in -le. If the word means main or a person or a sum of money, use -al.
More confusing words
Make vs do
Make creates a result you can point at. Do performs a job or activity, often a routine one. The fixed phrases decide the rest.
Bring vs take
Bring moves something here, to the speaker or the shared place. Take moves something there, away from the speaker.
Hear vs listen
Hear is what reaches your ears without trying. Listen means you pay attention to the sound on purpose.
Browse all the confusing word pairs or take the free A1 to C2 level test to find your starting point.