Struggling with Words, Part 2: Principal or Principle?

[This is the second in a series of posts on commonly confused words.]

Oh, if I had a dollar for every time I heard that an elementary school teacher taught someone, "You can tell the difference between principal and principle since the principal is your pal."

Not a very helpful tip because when I saw what was due on my first home mortgage statement, I said, "That amount is not my pal." But a capital sum placed at interest is also principal, and so is a chief, or principal, reason for doing something.

So while the following tip might not be as cute as the elementary school teacher's, it is certainly more helpful: principal means chief. Examples:

• The principal (chief of the school) dismissed the students.
• The principals (chiefs of the company) decided to issue an IPO of their company stock.
• The principal (chief) function of the manual is to guide you in using the software program.
• The principal (chief part) of the loan is $400,000.

Then what is principle? A fundamental belief or rule. Examples:

• The right to vote is a principle of democracy.
• She will not compromise her principles. 

So here's a principal principle about error-free writing: when in doubt, look it up.