Comma Before Which | Correct Use & Examples

Commas updated on  January 5, 2024 4 min read
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.

Examples: Comma before “which” introducing a nonrestrictive clause
The skyscraper, which was built in the 1930s, is being renovated.
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.

Examples: “Which” introducing a restrictive clause
The cat which lives next door is very friendly.
The book which I’m reading is a bestseller.

Tip
If you’re unsure whether a comma is needed before “which,” try omitting the “which” clause from the sentence:
  • 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.

Example: Nonrestrictive “which” clause
Our car, which we bought last year, gets good mileage.
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.

Example: Comma before and after “which” 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.

Example: Restrictive “which” clause
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.

Example: Which vs that
The university which I attended is renowned for its engineering program.
The university that I attended is renowned for its engineering program.

Note
In UK English, “that” is the most common way to introduce restrictive clauses, but “which” is also considered an acceptable option and is generally used in more formal contexts.

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).

Examples: Using “which” in direct and indirect questions
Which hotel do you want to stay at?
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.

Examples: “Which” after a preposition
The local football team, of which he is the captain, won the championship last year.
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.

Examples: “Which” followed by an interrupter
Mark watched a movie, which, incidentally, was filmed in his hometown.
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).
Do you want to know more about commas, parts of speech, email, or other language topics? Check out some of our other language articles full of examples and quizzes.


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Comma before or after but

Noun clauses

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Comma before too

Predicate nominative

Affective vs effective

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Eoghan Ryan

Eoghan has taught university English courses on effective research and writing. He is particularly interested in language, poetry, and storytelling.

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