"Which" vs "That": The Rule for Extra and Necessary Information
Which vs that — the restrictive vs non-restrictive clause rule, comma usage, and when the choice changes meaning.
The book that I read was excellent.
The book, which I read last week, was excellent.
Both sentences are about a book you read. But the grammar is different — and the difference is about necessity and commas.
A restrictive clause identifies which specific thing you mean. Without it, the sentence loses its meaning.
The car that is parked outside is mine.
Without “that is parked outside,” you don’t know which car. The clause is essential. No commas. Use that (preferred in American English) or which (acceptable in British English).
More examples:
The phone that I bought yesterday stopped working.
Students that study regularly perform better.
The movie that we watched was boring.
- No commas
- Essential to identify the noun
- Use that (AmE preference) or which (BrE)
A non-restrictive clause adds bonus information about something already identified. The clause can be removed without losing the main point.
My car, which is parked outside, needs washing.
You already know which car (my car). The clause “which is parked outside” is just extra information. It must be set off by commas. Always use which — never “that.”
More examples:
My laptop, which cost ₹50,000, is very slow.
The Taj Mahal, which is in Agra, is a UNESCO World Heritage Site.
She gave me her number, which I promptly lost.
- Always uses commas
- Extra, non-essential information
- Always use which (never “that”)
The easiest way to decide:
- Need commas? → Use which.
- No commas? → Use that (or “which” in British English).
Ask yourself: “If I remove this clause, does the sentence still identify the right thing?”
The car that is outside is mine. (Remove the clause → “The car is mine” — which car? Essential → no commas → that)
My car, which is outside, is red. (Remove the clause → “My car is red” — still clear which car. Extra info → commas → which)
- American English: Strict distinction — “that” for restrictive, “which” for non-restrictive.
- British English: “Which” is often used for both types.
For Indian exams, follow the American distinction — it is what most exams test.
There are cases where “that” is required, even in British English:
This is the best movie that I’ve ever seen.
She is the most talented singer that the school has produced.
All that glitters is not gold.
Everything that happened was unexpected.
She was the only person that helped me.
This is the first time that I’ve been here.
He was the very student that the teacher praised.
Incorrect: My laptop, that cost ₹50,000, is slow
Correct: My laptop, which cost ₹50,000, is slow.
Non-restrictive clause (commas) → use “which,” not “that.”
Informal BrE: The phone which I bought yesterday is great.
Formal AmE: The phone that I bought yesterday is great.
Restrictive clause (no commas) → “that” is preferred in American English.
Incorrect: My car which is outside needs washing.
Correct: My car, which is outside, needs washing.
Non-restrictive clauses must be set off by commas.
- The book ___ I borrowed from the library was fascinating.
- My house ___ is near the market is very old.
- The phone ___ I bought last month has stopped working.
- Her new novel ___ was published last week is a bestseller.
- All ___ is needed is patience.
- that — restrictive (no commas, identifies which book)
- which — non-restrictive (commas needed: “My house, which is near the market, is very old”)
- that — restrictive (no commas, identifies which phone)
- which — non-restrictive (commas needed: “Her new novel, which was published last week, is a bestseller”)
- that — after “all,” use “that”
- Restrictive (essential, no commas) → that (or “which” in BrE)
- Non-restrictive (extra info, commas) → which only
- After superlatives, “all,” “every,” “the only” → that
- The comma test: commas → which; no commas → that