Generations of teachers have tried to drill this one into students’ heads by reminding them, “The principal is your pal.” Many don’t seem convinced. “Principal” is a noun and adjective referring to someone or something which is highest in rank or importance. (In a loan, the principal is the more substantial part of the money, the interest is—or should be—the lesser.) “Principle” is only a noun, and has to do with law or doctrine: “The workers fought hard for the principle of collective bargaining.”
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