Principal is a noun or an adjective: the head of a school, a main person, a sum of money, or simply "main". Principle is only a noun: a rule, a belief, or a basic truth. If you can replace the word with main, write principal.
Words that sound the same or are spelled almost the same can be very confusing, and people often have a hard time deciding which one to use. Principle and principal are a good example. They have completely different meanings, but they sound identical. So how can you tell which one to use? Here is the best way to make that decision.
They are called homophones
English has many words that sound alike. Words like these are called homophones. For many students and writers, they cause headaches and lead to mistakes. Right, rite, and write, or to, too, and two, are just a few of a long list. (The difference between homonyms, homophones, and homographs explains the terms.) Luckily, there are some tricks that help you remember which one to choose.
Using principal
Principal is both a noun and an adjective, so which meaning it has depends on how it is used.
As a noun, principal most often means the head of a school or of another organization:
The principal of my high school is Mr. Evans.
As an adjective, principal means the same as main, chief, primary, or leading:
The principal suspect in the armed robbery was caught 2 days ago.
Vegetables are the principal ingredients in most soups.
Tourism is the principal source of income on the island.
In the last sentence, principal modifies the word source: it says that tourism is the main source of the island's income.
One use of principal that often causes problems is its meaning in finance: the original sum of money that was lent or invested, as opposed to the interest on it.
The banker told me that the payments would be applied to the interest first, and then to the principal.
He was worried about his money, but the bond will repay its principal amount when it matures.
Using principle
Principle is a bit easier to use, because unlike principal, which is both a noun and an adjective, principle is only a noun. It usually means a belief or a moral rule that helps you tell right from wrong:
Although many questioned his motives, Hector stuck to his principles.
Some people lie, but others believe it is against their principles to fib.
Principle also means a basic rule, law, or truth that something is based on, or the idea behind it:
Once you understand the principles behind calculus, it becomes a lot easier.
In principle, the investment was a great idea.
Here is one sentence that uses the words correctly, to help you remember them:
Stand next to your principal, as you hold fast to your principles regarding these principal rules.
Keep this in mind
With homophones, it is all a matter of practice and of remembering the rules. Two tricks help you tell principal and principle apart:
- The principal of your school is your pal: princi-PAL ends in pal.
- A principle is a rule: princip-LE and ru-LE both end in le.
And when you need an adjective, it is always principal, because principle is never an adjective. If main fits in its place, principal is right.
For more help with tricky words and rules, read who or whom and six important grammar rules you need to know.