I saw an interview with an agent who said she was tired to getting query letters saying someone has written a “fictional novel.” All novels are fiction. Otherwise, it’s a memoir or autobiography or some other kind of non-fiction. I’ve also heard this mistake from people who should know better. Here are two pairs that often get mixed up:
Principle/principal:
A principle is a fundamental law of truth or tenet. (His principles wouldn’t allow him to go along with bribery.)
Principal means the foremost (His principal concern is making money) or the head of a school, or a lead actor, or (in law) a person who authorizes another to represent him or her.
Complements/compliments:
“Complements” is a verb that means completes or makes perfect something else. (They make a great couple because his sense of humor complements her serious nature.)
Compliments relates to praise (She got several compliments on her new dress, He compliments everybody) or to give a present (He sent the flowers with his compliments).
Complimentary champagne is free. Complementary medicine is a useful counterpart to traditional medicine (although some people disagree).