Skip to main content

Principal vs Principle


  • ‘Principal’ (adj) means ‘main; most important’.
  • ‘Principle’ (adj) means ‘a proposition, theorem or idea’.

What’s the difference between ‘principal’ and ‘principle’?

It is easy to misspell and therefore confuse the two, but they are very different in usage and meaning.

  • ‘Principal’ is an adjective, which combines with nouns like ‘objectives’, ‘components’, ‘measures’, or ‘findings’ in academic texts. It is also frequently used in the phrase ‘principal investigator’ (PI), referring to the lead researcher for a project/main holder of a grant.
  • ‘Principle’ is a noun, and is also frequently used in academic texts due to its scholarly meaning (a proposition, theorem or idea).

Writing tip: Want to make sure your writing is accurate and academic-like? Writefull gives you the best language feedback on your texts, plus clever AI widgets to help you write. Install now.

How they’re used

Example sentences with ‘principal’

  • We introduce an algorithm for producing approximate principal components.
  • They are the principal techniques used to understand outer layers of substrates.

Example sentences with ‘principle’

  • The authors were the first to introduce the principle of relativity.
  • Our paper presents an extension of Banach's contraction principle.