That vs Which: When to Use Each
I used to guess. I'd write a sentence, pause at "that" or "which," pick one that sounded right, and move on. Turns out there's an actual rule — and once you learn it, you stop guessing forever.
The Core Distinction: Restrictive vs Non-Restrictive
The difference between "that" and "which" comes down to whether the clause is essential to the meaning of the sentence.
"That" introduces a restrictive clause — a clause you can't remove without changing the sentence's meaning. No commas.
"Which" introduces a non-restrictive clause — a clause that adds extra information but can be removed without changing the core meaning. Always set off with commas.
Here's the clearest example pair in the English language:
Restrictive (that, no commas): My car that has a sunroof gets terrible gas mileage.
This sentence implies I own multiple cars. The clause "that has a sunroof" tells you which car I'm talking about. If you remove it — My car gets terrible gas mileage — the meaning changes. You no longer know which car.
Non-restrictive (which, commas): My car, which has a sunroof, gets terrible gas mileage.
This sentence implies I own one car. The clause "which has a sunroof" is bonus information. If you remove it — My car gets terrible gas mileage — the core meaning stays intact. You still know which car: my only car.
The Comma Rule
Here's the shortcut: "That" never takes commas. "Which" (in this usage) always takes commas.
If you see commas around the clause, use "which." If there are no commas, use "that." This rule works in American English about 98% of the time.
- The report that I submitted yesterday has an error. (No commas — "that" — specifies which report)
- The quarterly report, which I submitted yesterday, has an error. (Commas — "which" — adds a side note about the report)
- Recipes that call for fresh herbs taste better. (No commas — restricts to a subset of recipes)
- Her grandmother's recipes, which she keeps in a worn binder, are legendary. (Commas — extra detail about the recipes)
The Removal Test
Not sure which one to use? Try this: Remove the clause and see if the sentence's fundamental meaning changes.
Test 1: Laptops ____ have SSD drives boot faster.
Remove the clause: Laptops boot faster. Does the meaning change? Yes — not all laptops boot faster, only those with SSDs. The clause is essential. Use that: Laptops that have SSD drives boot faster.
Test 2: My laptop, ____ has an SSD drive, boots fast.
Remove the clause: My laptop boots fast. Does the meaning change? No — the SSD detail is extra information. The clause is non-essential. Use which: My laptop, which has an SSD drive, boots fast.
American vs British English
Here's where it gets interesting. The "that = restrictive, which = non-restrictive" rule is solidly American. British English is looser.
In British English, "which" can be used for restrictive clauses too. A British writer might say "The book which I borrowed from you was excellent" — and that's considered fine. An American editor would change that to "The book that I borrowed from you was excellent."
However, even in British English, "that" is never used for non-restrictive clauses. Nobody writes "My mother, that lives in Toronto, is visiting." That sounds wrong to everyone.
If you're writing for an international audience, stick with the American rule. It's clearer, and it's never wrong — even in the UK. British readers will understand you perfectly; they just might think you're being a bit formal.
Real-World Examples, Fixed
Wrong: The policy which affects remote workers was updated last week.
Fixed: The policy that affects remote workers was updated last week. (Assuming there are multiple policies and this clause identifies which one.)
Wrong: The new policy, that affects all remote workers, was updated last week.
Fixed: The new policy, which affects all remote workers, was updated last week. (Commas signal non-restrictive — must use "which.")
Wrong: I finally deleted the app, that was draining my battery.
Fixed: I finally deleted the app that was draining my battery. (No comma — restrictive — "that.")
When You Can Skip Both
Sometimes you can drop "that" entirely. When "that" is the object of the restrictive clause, it's optional:
- The coffee that I ordered is cold.
- The coffee I ordered is cold. (Same meaning, slightly smoother.)
But when "that" is the subject of the clause, you can't drop it:
- The coffee that spilled on my keyboard ruined my morning.
- The coffee spilled on my keyboard ruined my morning. (This means something different — now "spilled" is the main verb, not part of a relative clause.)
For a deeper dive on sentence structure issues like this, check our guide to dangling modifiers. And if you want to catch that/which errors automatically, paste your text into our grammar checker — it flags these instantly, along with its vs it's confusion and semicolon mistakes.
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