When two words sound alike, and when they’re not words we use on a daily basis, confusion is inevitable. Such is the case with ‘principal’ and ‘principle’.
But these terms each have specific uses, so you won’t want to mix them up in your written work.
Principal (Most Important)
The main use of ‘principal’ is as an adjective meaning ‘most important’:
The principal aim of the project is to locate the end of a rainbow.
(Photo: Wing-Chi Poon/wikimedia)
But it can also be used as a noun, usually to describe the chief or head of something. The head of a school or college, for example, is sometimes called the ‘principal’ (especially in the USA):
As school principal, Ms Harkness was responsible for hundreds of children.
It can also apply to the lead actor in a play or the lead instrumentalist in an orchestra.
‘Principal’ also has technical uses in legal settings, such as identifying the main person responsible for a crime (as compared to an ‘accessory’, who assists in a crime). Make sure to check the legal uses of this term if you’re writing about law, as they can be quite specific.
Principle (A Fundamental Law or Belief)
‘Principle’ is always a noun. One use is to refer to a fundamental rule or law:
The principles of quantum physics suggest that rainbows are impossible.
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(Image: Varsha Y S/wikimedia)
Another meaning of ‘principle’ is ‘an accepted rule of conduct’, particularly a moral rule:
As a woman of principle, Ms Harkness promotes learning for all.
This is also why we say we believe something ‘in principle’ if we agree with the general idea (even if there are reasons for not acting on the belief in practice).
Principal or Principle?
‘Principle’ is always a noun, whereas ‘principal’ can be either a noun or an adjective. So if you’re describing something as the most important or first of something, the word you’ll need is ‘principal’.
And if you keep in mind that ‘principal’ is an adjective meaning ‘most important’, you can use this as a reminder that it’s also a word to describe the main or most significant person in a group.
After that, it should be easy to recall that a ‘principle’ is a rule, law or guideline. Remember:
Principal = Most important (adjective) or head/chief (noun)
Principle = Rule or law (noun)