Do you compliment someone or complement them? Both could be right. These two words are often confused or typoed into each other. I added them to my checklist in PerfectIt a couple of years ago after seeing them mixed up in three manuscripts by three different authors in one week.
Both words can be used as nouns or verbs, and they have similar adjective forms (complimentary and complementary) as well.
A compliment is an expression of praise, respect, or greetings. The plural is compliments, which can also refer to something that’s given away for free.
- She complimented the detailers on how clean her car was.
- He sends his compliments.
- The owner sent a bottle of wine, compliments of the house.
A complement is something that goes well with or completes something else, or the number of things or people to fill something.
- The ship sailed with a full complement.
- Liberal arts courses should be required in order to complement a technical education.
Complement also has many similar senses in math and science. For example:
- The complement system in the body refers to proteins produced by the liver as part of the immune system.
- The angle B that can be added to another angle A to make up a 90-degree angle is the complement of A.
- Given a subset A of set B, the complement is the subset of B containing items not in A.
- The negation of a logical statement is its complement.
There are times when ambiguity may make the choice not completely clear:
- The waiter presented a bottle of complimentary wine for their meal.
Is the wine free, in which case the sentence is correct (though “complimentary bottle of wine” may work better)? Or does it go well with the food, in which case it should be complementary? Situations like this call for an editor’s comment, complemented with some complimentary suggested rewordings.
References
- Merriam-Webster Unabridged entries for complement and compliment.
- Oxford English Dictionary entries for complement and compliment.
- Complement System – Physiopedia