Comma Before Which | Rules & Examples
“Which” is a relative pronoun used to introduce a relative clause. Whether you need a comma before “which” depends on which kind of relative clause it introduces:
- You need a comma before “which” when it introduces a nonrestrictive clause: a clause providing extra information that isn’t essential to the sentence’s meaning.
- There’s no comma before “which“ when it introduces a restrictive clause: a clause that couldn’t be removed without changing the sentence’s meaning.
|“Which” introducing a nonrestrictive clause (comma)
|“Which” introducing a restrictive clause (no comma)
|My car, which is a blue Ford Focus, was stolen last week.
|The car which was reported stolen was a blue Ford Focus.
|I can’t wait for Christmas, which is my favourite holiday.
|The subjects which I struggle most with are chemistry and history.
Comma before “which”: Nonrestrictive clause
“Which” is most commonly used to introduce extra information that isn’t essential to the meaning of the sentence. This kind of “which” clause is called a nonrestrictive clause or a nonessential clause. It’s always set off from the rest of the sentence by commas.
You can tell that a “which” clause is nonrestrictive if it can be removed without affecting the basic meaning of the sentence:
- My grandmother’s house, which stands on top of the hill overlooking town, was built over a century ago.
- My grandmother’s house was built over a century ago.
The sentence still makes the same basic statement without the “which” clause. The subject is clear without the extra information, so it’s still obvious what house is being referred to: the one belonging to the speaker’s grandmother. Therefore, the clause must be surrounded by commas.
Note that if the “which” clause appears in the middle of the sentence, you need a comma at the end of the clause as well as at the beginning. Don’t forget the second comma:
- I drank a cup of coffee, which helped to wake me up and went to work.
- I drank a cup of coffee, which helped to wake me up, and went to work.
No comma before “which”: Restrictive clause
“Which” is sometimes used instead to introduce a restrictive clause (or essential clause): a clause that’s necessary to express the sentence’s meaning.
This kind of “which” clause is needed to define what you’re referring to. It can’t be removed without making the sentence’s meaning unclear or much less specific. Restrictive clauses must not be set off by commas.
Check whether a clause is restrictive by seeing what the sentence looks like if you remove it:
- The genre of music which I like best is R&B.
- The genre of music is R&B.
The sentence without the “which” clause no longer makes any clear statement. It’s now unclear what the subject “the genre of music” refers to. What genre of music? So the “which” clause is restrictive and should be written without commas.
Which vs. that
In US English, most style guides recommend using “that” instead of “which” to introduce a restrictive clause. So the example above would become “The genre of music that I like best is R&B.” In UK English, some language authorities give the same recommendation, but it’s largely ignored in practice.
This rule is useful because it more clearly distinguishes restrictive clauses from nonrestrictive clauses. And “that” is never used in nonrestrictive clauses in either version of English (i.e., “My car, that is a blue Ford Focus, was stolen last week” is not grammatically correct), so the distinction is logical.
If you write in US English, you should always follow this rule. It’s optional in UK English, but it tends to be a good idea. It does no harm, usually makes your writing smoother, and avoids confusion about when to add a comma: if you only use “which” nonrestrictively, you’ll always add a comma before it.
- The historical period which fascinates me the most is the Renaissance.
- The historical period that fascinates me the most is the Renaissance.
“Which” in questions
“Which” is also used as a wh-word (specifically, an interrogative pronoun or interrogative determiner) to introduce a question. In a direct question, it appears at the start, so there’s obviously no need for a comma before it, and you also should not add a comma after it.
“Which” is also used in indirect questions – sentences that don’t end in question marks but still implicitly ask a question or refer to a question asked in some other context. Again, no commas should be added before or after “which” in this context.
“Which” after a preposition
“Which” also commonly appears directly after a preposition (e.g., “in which”, “between which”, “with which”). You should never place a comma between the preposition and “which”, and there’s also no need for a comma after “which” in these phrases.
You do have to add commas around the whole “which” clause if it is nonrestrictive. The rules are the same as those described earlier, except that the comma appears before the preposition, not directly before “which”. And, as above, no commas are needed in a restrictive clause.
Is there ever a comma after “which”?
It’s usually wrong to insert a comma after “which”. In most cases, there’s no reason to do so:
- Jane went to the supermarket, which, was just around the corner from her house.
The only context where you should add a comma after “which” is when it’s followed by an interrupter – a phrase that interrupts the sentence to qualify or emphasize some part of the statement. Interrupters should be set off with commas on both sides.
Worksheet: Comma before or after “which”
You can test your knowledge of when you need a comma before or after “which” with the worksheet below. Just add commas wherever you think they’re needed to the example sentences, and then check them against the answers provided.
Other interesting language articles
If you want to know more about commonly confused words, definitions, common mistakes, and differences between US and UK spellings, make sure to check out some of our other language articles with explanations, examples, and quizzes.
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