Comma Before Which | Correct Use & Examples
The relative pronoun “which” is used to introduce a relative or adjectival clause.
You should put a comma before “which” when it’s used to introduce a nonrestrictive clause—a clause that provides information that is not essential to the meaning of the sentence.
She wore a beautiful necklace, which was a gift from her grandmother.
You don’t need a comma before “which” when it’s used to introduce a restrictive clause—a clause that provides essential information, without which the sentence wouldn’t make sense or would mean something else.
The book which I’m reading is a bestseller.
- If the basic meaning of the sentence doesn’t change, a comma is required (e.g., “The skyscraper is being renovated”).
- If the meaning of the sentence is unclear or less specific, no comma is needed (e.g., “The cat is very friendly”; what cat?).
When to use a comma before which
You need a comma before “which” (and at the end of the clause) when it’s used to introduce a nonrestrictive or nonessential clause.
A clause is nonrestrictive if it provides nonessential information that can be removed without impacting the fundamental meaning of a sentence.
Our car gets good mileage.
The basic meaning of the sentence above is not affected by the omission of the “which” clause. The subject (“our car”) is already clearly identified, so there’s no confusion about what car is being discussed.
This clause is nonrestrictive, so it should be set off from the rest of the sentence with commas. As it appears in the middle of the sentence, commas are needed both before and after the clause.
- The restaurant, which serves Italian food is popular among locals.
- The restaurant, which serves Italian food, is popular among locals.
When you don’t need a comma before “which”
No commas are needed before “which” when it’s used to introduce a restrictive or essential clause that specifies what you are referring to.
A clause is restrictive if it provides essential information. Restrictive clauses can’t be removed without significantly affecting the meaning and clarity of a sentence. They should never be set off with commas.
- The company which I work for has won many awards.
- The company has won many awards.
When the “which” clause is removed, the sentence above is much less specific. It is unclear what company the speaker is referring to. Therefore, the “which” clause is restrictive and no commas should be used.
Which vs that
In US English, style guides generally advise using “that” at the start of a restrictive clause, not “which.”
This rule helps to distinguish nonrestrictive clauses from restrictive clauses. Additionally, “that” should never be used in a nonrestrictive clause (e.g., it’s incorrect to say “The skyscraper, that was built in the 1930s, is being renovated”).
This rule also removes any uncertainty about when to use a comma. If “which” is only used to introduce a nonrestrictive clause, it will always be preceded by a comma.
- The university which I attended is renowned for its engineering program.
- The university that I attended is renowned for its engineering program.
However, as with US English, “that” is never used to introduce a nonrestrictive clause, so the words cannot always be used interchangeably. Following the US English rule in UK English is not necessary, but it does reduce your risk of making a mistake.
You can also use the QuillBot Grammar Checker to check for this and other mistakes.
Using which in questions
“Which” can also be used as a wh-word (i.e., as an interrogative determiner or interrogative pronoun) to ask a question.
When “which” is used at the start of a question, no comma should be used before or after it. You also should not include commas when “which” is used in an indirect question (i.e., a sentence that contains an implicit question or one that describes a question that was asked in another context).
The waiter asked me which wine I preferred.
Aria wondered which bus she should take.
Using which after a preposition
When “which” appears after a preposition (e.g., “of which,” “for which,” “to which”), a comma should never be placed between the preposition and “which.” In these instances, no comma is needed after “which” either.
However, if it is part of a nonrestrictive clause, you should include a comma before and after the clause. In these instances, the comma should not be placed directly before “which.” Instead, it should be placed before the preposition.
If the clause is restrictive, no commas should be included.
The key with which I opened the door is rusty.
When to use a comma after which
A comma should only appear after “which” when it’s followed by an interrupter (i.e., a parenthetical expression that qualifies the statement or adds emphasis). In these instances, a comma should also appear after the interrupter.
John attended the seminar, which, to his surprise, was led by a renowned expert.
Quiz: Comma before or after which
Test your knowledge about when to use a comma before or after “which” with the quiz below. Add commas wherever you think they are needed (some sentences may not need any commas).