That, Which, or Who?

If you are referring to people, use who instead of that:

Correct: John Smith, the book editor who corrected all the mistakes in the 97,000 word book, received a nice mention in the author’s acknowledgements.

Incorrect: John Smith, the book editor that corrected all the mistakes in the 97,000 word book, received a nice mention in the author’s acknowledgements.

Use that instead of which with restrictive clauses.

Correct: This is the rule that people that people break most often.
Incorrect: This is the rule which people break most often.

Use which instead of that for non-restrictive clauses.

Correct: This is the correct rule, which many people overlook.
Incorrect: This is the correct rule, that many people overlook.

Quick tip: If a comma seems appropriate in the sentence, “which” is likely the correct word to use.

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