Few word pairs cause as much second-guessing as principal vs principle, and the confusion makes sense since they sound identical but mean completely different things. Principal usually refers to a person in charge, like a school principal, or something of primary importance. Principle, on the other hand, is a fundamental truth or rule someone lives by. A quick memory trick: "principal" ends in "pal," like the person leading your school. That small detail alone clears up most of the confusion instantly.