When do I use "that" versus "which"?

Use that for information the sentence needs. Use which for an aside you could remove.

Do you put a comma before "which"?

Usually yes — which introduces extra information, and that kind of clause takes commas on both sides.

Quick answer Canonicalizes to That vs. Which

Is it "the book that I read" or "the book which I read"?

Q: Is it "the book that I read" or "the book which I read"?

In edited American English, "the book that I read." Which sounds natural in British English. American usage reserves that for essential clauses and which for asides. "The book that I read" identifies which book — essential. British usage is more relaxed and often uses which in both slots. Either is grammatical; pick one and be consistent.

i · AnswerOne line, no lecture

In edited American English, "the book that I read." Which sounds natural in British English.

ii · A little moreWhy this is the one to keep

American usage reserves that for essential clauses and which for asides. "The book that I read" identifies which book — essential. British usage is more relaxed and often uses which in both slots. Either is grammatical; pick one and be consistent.

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