Common mistakes
Principle or principal: rules, people, and spelling
Sign in to savePrinciple and principal sound alike, but their meanings point in different directions. One is an idea or rule. The other can name a person, the most important thing, or an amount of money.
Choose principle or principal by deciding whether the sentence means a rule or belief, a leading person or thing, or an original amount of money.
Read and practice
Read the examples and try the written questions in this guide. Listening recordings are not available for this lesson yet.
Try the written questions
principle / principal /ˈprɪnsəpəl/ /ˈprɪnsəpəl/
The short answer
A principle is a rule or belief, as in a matter of principle. A principal is a leading person or thing, such as a school principal or the principal reason. In finance, principal is the original amount of money before interest.
The principal explained that fairness is an important principle at the school.
Why it works: The principal is the school leader; principle is the rule or value being discussed.
5 more examples
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Honesty is a principle that guides her work.
The sentence names a belief or standard.
Not this:Honesty is
a principalthat guides her work. What changes: A principal is not a belief or standard, so this spelling does not fit. -
The school principal welcomed the new students.
Principal names the person who leads the school.
Not this:The
school principlewelcomed the new students. What changes: A principle cannot welcome students because it is an idea, not a person. -
Safety was the principal reason for the delay.
Principal means most important in this phrase.
Not this:Safety was the
principle reasonfor the delay. What changes: The phrase needs an adjective meaning main, so principal is correct. -
Each monthly payment reduced the principal on the loan.
In finance, principal is the original amount borrowed, separate from interest.
Not this:Each monthly payment reduced
the principleon the loan. What changes: A payment reduces money owed, not an abstract rule. -
They disagreed on principle, even though the plan was cheap.
The phrase means because of a belief about what is right or fair.
Not this:They disagreed
on principal, even though the plan was cheap. What changes: On principal is not the usual expression for acting from a belief.
Read the full guide
Ask what the word names. If it names an idea that guides behavior, write principle. If it names a leader, the main item, or an original sum of money, write principal.
Use principle for an idea or rule
A principle is a rule, belief, or basic idea. It often appears in discussions of behavior, law, science, and work. If the word could mean a standard that guides a choice, use principle.
She would not share the private details because of a principle about trust.
The word names the belief about trust. It does not name a person or a main item.
Use principal for a leading person
A principal can be the person in charge of a school. It can also refer to a leading person in an organization or agreement. The meaning is a role held by a person.
The principal asked parents to arrive before the presentation.
A school principle might be a rule at the school, but it cannot be the person who asked parents to arrive.
Use principal for the main thing
Before a noun, principal can mean main or most important. This use often appears with words such as reason, concern, route, and aim.
Cost was the principal concern during the meeting.
Does the sentence mean a belief about cost, or the most important concern?
It means the most important concern, so principal is the right spelling.
Recognize principal in money language
In finance, principal is the original amount of money in a loan or investment. Interest is an extra amount paid or earned in relation to that principal.
The borrower paid interest as well as part of the principal.
This is a money meaning. A principle is never the amount borrowed.
Use on principle for a belief
The phrase on principle means because of a belief about what is right, fair, or acceptable. It does not mean because of a school leader or an important person.
He returned the extra change on principle.
What guided his action in this sentence?
A belief about honesty guided it, so the sentence needs principle.
Before you go
Remember this
Use principle for a rule, belief, or basic idea. Use principal for a leader, the main person or thing, or the original amount of money. Look for the meaning before you rely on the sound.
Practice with the written examples
You can practice with the written questions in the Learn tab. Each answer includes an explanation.
Try the written questionsListening test not available yet
This lesson does not have the recordings needed for a listening test. Use the written questions in the guide to check your understanding.
Try the written questionsQuestions about "Principle or principal: rules, people, and spelling"
What is the main difference between principle and principal?
Principle means a rule, belief, or basic idea. Principal can mean a leading person, the most important thing, or the original amount of money in a loan. In Honesty is a principle that guides her work, the word names a belief.
Honesty is a principle that guides her work.
Is the head of a school a principal or a principle?
The person who leads a school is a principal. In The school principal welcomed the new students, principal names a person. A school principle would be a rule or value, not the school leader.
Honesty is a principal that guides her work.
When does principal mean most important?
Principal means most important when it comes before a noun such as reason, concern, route, or aim. In Safety was the principal reason for the delay, it identifies the main reason.
The school principal welcomed the new students.
What does principal mean in a loan?
In a loan, principal is the original amount borrowed or still owed before interest. Each monthly payment reduced the principal on the loan uses the word in this financial sense.
The school principle welcomed the new students.
What does on principle mean?
On principle means because of a belief about what is right, fair, or acceptable. They disagreed on principle, even though the plan was cheap shows that the disagreement came from a belief.
Safety was the principal reason for the delay.