That vs which
Use which after a comma to add extra information about a thing, never that. Without a comma, both work, though American English prefers that. After a preposition, use which for things and whom for people. For people, use who, or that only without a comma.
A comma before extra details about a thing is your signal to choose which.
that pronoun
Begins a part of a sentence that tells exactly which person or thing you mean.
- The cake that you baked was delicious.
- She is the teacher that helped me pass the test.
which pronoun
After a comma, adds extra information about a thing just mentioned. Without a comma, it can also say exactly which thing you mean.
- Our new car, which is bright red, is easy to find in parking lots.
- The book which I borrowed from you is on the table.
Watch out
- When you say exactly which one you mean, that can point to people or things, though who is more common for people. In these clauses, which points to things, but in questions it can ask about people: Which teacher do you have?The woman that lives next door is a nurse.
- Which also asks questions about a choice from a known group.Which one is yours, the blue car or the gray one?
- After a comma, which can comment on the whole statement before it, not just on one noun.It rained all week, which is why the game was postponed.
Test yourself
The keys blank I lost were in my coat pocket.
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Either. No comma, and it says exactly which keys, so both work. American English usually prefers that here.
My bike, blank is ten years old, still works well.
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which. It comes after a comma and adds extra information about a thing, so use which.
The man blank fixed our roof did a great job.
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that. The man is a person. That works for people, but which is for things.
blank of these two coats is warmer?
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which. This question asks you to choose one from a group, and which asks that kind of question.