It’s amazing how many people use these two words incorrectly.
Principal is the name that you give the person who is in charge of an elementary or secondary school. He—or she—is the ‘main one.’ That’s what principal means. So whether you are talking about the administrator in a school or you are trying to point out that something receives the highest consideration, principal is the word you want.
A principle is an essential belief or a guiding rule.
Let’s say the principal’s name is Mr. Jones, and his main concern is the morals of his students. Now communicate that idea using principal and principle. You will use one of the words twice.
The principal’s principal concern was the moral principles of the students.
Let’s agree NOT to use both words in the same sentence, okay? You get the idea . . .