Short answer: Use that for information the sentence needs to identify something (no commas). Use which for extra information you could remove (with commas).
This is the rule taught by most American style guides. British usage is looser, and you will see which used in both places.
Restrictive vs. nonrestrictive clauses
| Type | Word | Commas? | Example |
|---|---|---|---|
| Restrictive (essential) | that | No | The car that hit me was red. |
| Nonrestrictive (extra) | which | Yes | My car, which is red, needs a wash. |
The deletion test: remove the clause. If the sentence still identifies the same thing, the clause is extra, so use , which. If removing it changes the meaning, use that.
- The car that hit me was red. Without “that hit me” you no longer know which car, so the clause is essential.
- My car, which is red, needs a wash. You already know which car it is, so “which is red” is extra.
Other rules
- Never put a comma before that in a restrictive clause: write The book that I read, not The book, that I read.
- Which comes after a preposition: the house in which I grew up.
- Use who for people: The woman who called is my aunt. (Not “the woman that called,” in formal writing.)
Common mistakes
- The tools, that you need, are in the garage. Remove the commas and use that.
- My laptop that I bought last year stopped working. If you have only one laptop, use , which with commas.
Take the that vs. which quiz
1.The book ___ is on the table belongs to me.
2.My laptop, ___ I bought last year, stopped working.
3.Which sentence is punctuated correctly?
4.Which sentence contains a nonrestrictive clause?
5.She works for a company ___ makes software.
6.The report, ___ was 50 pages long, covered every detail.
7.This is the road ___ leads to the lake.
8.In which sentence can you delete the clause without changing the meaning of the main sentence?
9.The meeting, ___ was scheduled for noon, was canceled.
10.In formal American writing, which sentence is preferred?
Frequently asked questions
What is the difference between that and which?
Use that for essential information with no commas. Use which for extra information with commas.
Can I use which instead of that?
In British English, often yes. Most American style guides prefer that for essential clauses, so use that in US writing.
Do I put a comma before which?
Yes, when which begins an extra (nonrestrictive) clause. Do not put a comma before that in an essential clause.
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