Complement vs Compliment: which is correct?

Complete versus praise

Complement, with an e in the middle, is about completing. A complement is something that completes, perfects, or goes well with something else, making a satisfying whole. A scarf can complement a coat, a sauce can complement a dish, two people's skills can complement each other. The word also means a complete set or full quantity, as in a full complement of crew, meaning the whole required number. Whenever the idea is completing or pairing well to make a whole, the word is complement.

Compliment, with an i, is about praise. A compliment is a polite expression of admiration: she gave me a compliment on my work. As a verb, to compliment someone is to praise them: he complimented the chef. The plural compliments also appears in set phrases like compliments of the season or with our compliments, meaning best wishes or something given free as a courtesy. Whenever the idea is praise or a courteous gesture, the word is compliment.

The spelling clue that always works

The reliable mnemonic is built into the words. Complement and complete both contain ple and, crucially, the same e: complEment completes. If the thing is finishing or perfecting something else, choose the e spelling, complement. This single link, e for complete, resolves the pair instantly and is the trick most editors actually use.

For the i spelling, a common hook is that compliment and I like it both lean on the i sound, and a compliment is something you like to receive. Another is that you give a complIment, and praise is something that makes someone feel good, with the i standing in for the warm I of personal feeling. Either works, but the complement-completes-with-an-e link is the load-bearing one; once you have that, compliment is simply the other spelling, the praise.

Examples on both sides

Complement (completes or pairs well): the blue trim complements the grey walls; this wine complements the cheese beautifully; her analytical strengths complement his creative ones; the ship sailed with a full complement of officers; a side salad is the perfect complement to the main course. Each is about completing a whole or matching well.

Compliment (praise or courtesy): thank you for the compliment; he is quick to compliment good work; the review was full of compliments; please accept this dessert with our compliments; she blushed at the unexpected compliment. Each is about praise or a gracious gesture.

Notice the derived words follow the split too. Complementary means completing or matching, as in complementary colours or complementary skills. Complimentary means either praising (complimentary remarks) or free of charge (a complimentary breakfast). The free-of-charge sense flows naturally from the courtesy meaning of compliment: something given with the host's compliments. Keeping the root meanings straight keeps the adjectives straight as well.

Putting it into practice

When you proofread, ask one question at each occurrence: is this about completing or matching, or about praise? Completing means complement, the e spelling tied to complete. Praise or a free courtesy means compliment, the i spelling. Because the two meanings are quite different, the question almost answers itself once you pause to ask it.

Pay attention to the adjective forms, which are where careful writers slip. A complimentary copy of a book is a free one (courtesy), while complementary therapies are ones that complete or accompany conventional treatment. If you mean free, you want the i; if you mean completing, you want the e. Spell-check will not flag a swap because both spellings are valid, so the complete-with-an-e link has to live in your head. Run the quiz above, which mixes the completing sense, the full-set sense, and the praise sense, until the right vowel is automatic.