Mixing up principle and principal is quite a common error in speech and writing. The two words have shared roots in Latin, and they look very similar and sound the same, but in modern English they are have different meanings and are used for different purposes.
Principle is most often used as a noun, meaning a fundamental basis of a system of belief or thought, e.g., voting is the most important principle in a modern democracy.
Principal is most often used as an adjective, meaning main or most important, e.g., New York is one of the principal cities in the United States.
Both principal and principle have other meanings and contexts that will be discussed below.
Principle Definition
Principle, which is often pluralized to a mass noun as principles, is defined as a fundamental truth that serves as a foundation for a set of beliefs or behaviors. We talk about principles in the sense of rules, guidelines, laws and facts. Principle is always used as a noun. It can have slightly different meanings when presented in different contexts:
An accepted fundamental truth as a basis for belief in a system:
By refusing to hear the testimony of the witness, the judge was accused of ignoring one of the most basic principles of a fair trial.
In modern usage, principle has become a synonym for morals:
He was regarded as a man of principle.
A guiding rule that explains how something works:
Learning the basic principlesof composition help us communicate better.
Principle Examples
Here are some examples of principle used in a sentence
The opportunity to have an education should be one of the fundamental principles guiding human rights law.
He was a man without any principles, seemingly willing to shed his beliefs to suit the occasion.
I disagree with the principles of all religions.
All car engines work on the same set of principles.
The two most important principlesshe lived by were being friendly and being helpful to others.
In Principle
In principle, is a common phrase with two meanings:
In principle can mean that something is theoretically possible, but it probably won’t happen in reality. It is a synonym for in theory.
In principle, the banks could raise interest rates at any time, but they are unlikely to do so this year.
In principle can also mean a general idea or plan, with details yet to be firmly established.
She accepted the details of the investigation in principle, but she had more questions to ask the suspect.
Principal Definition
Unlike principle, principal can be used as both a noun and an adjective. As an adjective it can mean:
The first, main or most important:
Beef is the principalingredient in my favourite casserole recipe.
It can also mean the first sum of money invested in something:
The principal amount invested in the fund should be no less than $100,000.
As a noun, principal can mean the head of a school or other educational institution:
Mrs Brown had been school principalfor over 40 years.
It can also mean the owner or partner of a company:
Robert Kraft, principal of Kraft Group, also owns the New England Patriots.
It can also mean the lead position in a group of actors, musicians, dancers and so on:
As the principal actress in the play, she had her own dressing room.
Principal Examples
Here are some examples of principal used in a sentence:
The principal, Mr Rodgers, was absent from school for a week due to illness.
Cape Town, Johannesburg and Pretoria are the principal cities of South Africa.
Sarah was overjoyed to learn that she would become the orchestra’s principal cellist.
Unfortunately, the principal investment is not exempt from tax relief.
Plastic is the principal cause of ocean pollution.
Are principle and principal related?
As you can probably guess, principle and principal are related words. They have roots in Latin, with principium (meaning source) providing the base for principle, and principalis (meaning first) providing the root for principal. The words are also traced back to the princeps and princip, Latin words meaning first or chief.
