Do you always need a comma before which

Here are the general rules for when to use a comma with which:

• Place a comma before which if it is introducing a nonrestrictive phrase.
• Do not place a comma before which if it is part of a prepositional phrase like “in which.”
• Do not place a comma before which if it introduces an indirect question.

Nonrestrictive Phrases

Nonrestrictive phrases add extra, nonessential information about a noun phrase that was already mentioned in the sentence.

Celena’s new refrigerator, which is less than a week old, has started making a buzzing sound.

In this sentence, which introduces a nonrestrictive phrase. So, you need a comma both before which and at the end of the nonrestrictive phrase. This is a nonrestrictive phrase because you can take it out of the sentence, and the meaning doesn’t change.

Celena’s new refrigerator has started making a buzzing sound. 

Restrictive phrases can’t be taken out of the sentence without changing the meaning. Usually, restrictive phrases are introduced by that instead of which.

Refrigerators that Celena buys always seem to have problems.

The highlighted phrase is restrictive. If you take it out of the sentence, the meaning changes: Refrigerators always seem to have problems. You’re not talking about refrigerators in general; you’re specifically talking about the refrigerators that Celena buys. That means the phrase is restrictive and does not need commas. 

Examples of sentences that need a comma before which:

My new shoes, which were quite expensive, hurt my feet.

Her nonprofit organization, which she’d dreamed of for years, is finally starting.

Sally picked up the bag, which had fallen on the floor.

Prepositional Phrases with Which

Don’t add a comma before which if it is part of a prepositional phrase like of which, in which, or on which.

I watched three movies, the shortest of which lasted one hour. 

The box in which the gift arrived was full of holes.

The premise on which the book was based was far-fetched. 

Using Which in Questions

Do not add a comma before which if it introduces a question. 

She asked Paul which bus she should take.

Related: For more punctuation knowledge, check out our”Punctuation Pointers” section here!

Do you know when to use a comma before which — and when not to? 

Right.

That’s why you’re here. You’ve seen the word “which” used with and without commas.

And, chances are, you’ve also seen commas in places they shouldn’t be. 

You don’t need that confusion in your life.

And once you get through this post, you won’t have it.

You’ll know exactly when to put a comma with which. 

And you’ll be able to explain it to others like a seasoned pro.

The Quick and Dirty Rules on Commas Before “Which”

If you’re looking for a short answer to the question, “When do you put a comma before which?” the following rules sum it up nicely: 

• Yes to the comma — when “which” introduces a non-restrictive or defining clause;
• No to the comma — when “which” introduces a restrictive or defining clause;
• No to the comma — when “which” is part of a prepositional phrase;
• No to the comma — when “which” is part of an indirect question. 

When to Use A Comma Before “Which” 

So, the answer is “Yes” (to the comma) when the sentence as a whole could take or leave the (non-restrictive) clause set off with “which.” 

The comma is there to set it off as extraneous to the meaning of the larger sentence. 

Take out the non-restrictive (or non-defining) clause, and the meaning of the sentence stays the same. It may not communicate as much, but it still makes the same point. 

Examples: 

• Her car, which is the black compact SUV out front, is in dire need of a wash. 
• His job, which he’s had since 2016, is the best one he’s had so far.
• Her dog, which is now five years old, will always choose footwear over kibble. 

If you remove the “which” clause, the sentence still says the same thing; the meaning doesn’t change. 

• Her car is (still) in dire need of a wash.
• His job is (still) the best one he’s had so far. 
• Her dog will (still) always choose footwear over kibble. 

The extra information, since it’s not essential to the sentence’s meaning, feels more like an interruption — a break or pause in the flow of the sentence. It’s there to provide extra information. 

If it helps, you can tell yourself, “When ‘which’ has just gotta be ‘extra,’ you introduce it with a comma.” (Because comma rhymes with drama.)

When is there NOT a comma before which?

So, now that we’ve covered the ONE case with “which” that calls for a comma, let’s cover the cases where you’ll leave the comma out. 

Here’s a  quick refresher: 

• No → when “which” introduces a restrictive / defining clause; 
• No → when “which” is part of a prepositional phrase; 
• No → when “which” introduces an indirect question in a sentence

And now, for some examples, let’s start with restrictive clauses. They’re called “restrictive” because they restrict the scope of a sentence to the content introduced by the “which” clause. By doing so, they directly impact the meaning of the sentence. 

The “which” in these situations can be replaced with “that” (and often is). It can also be left out completely. In fact, the sentence often sounds better without either one. 

Examples of which with restrictive clauses: 

• “The apartment which/that she rents has a washer and dryer and walk-in closets” or “The apartment she rents has a washer…. “
• “The books which/that she keeps by her bed are her reading choices for this month” or “The books she keeps by her bed are her reading choices…. “ 
• “The cat which/that she adopted last month has torn her curtains to shreds” or “The cat she adopted last month has torn her curtains to shreds.” 

Next up are situations where “which” is part of a prepositional phrase used to avoid ending a sentence with a preposition. 

So, while you probably won’t hear them much in spoken English, using constructions like the following will make your favorite grammar purist very happy:

• On which
• In which
• Over which
• Beyond which
• With which
• Below which
• Above which
• For which
• By which

We could go on. Just take a preposition and add “which” and you can probably think of some examples like the following: 

Examples of which with prepositional phrases: 

• “The closet in which she found her coat also revealed something she never wanted to see.” 
• “Little did he know, the hook on which he rested his hat had just been painted.” 
• “The town from which she comes has a population of 123. Or it did until she left.” 
• “The name by which he’s been known actually belongs to his neighbor of two years ago, who hasn’t been heard from since.” 
• “The tools with which she fixed the car belonged to the gas station owner.” 

Finally, we get to the cases where “which” introduces an indirect or implied question. In this case, the which clause is the direct object of the preceding verb (ask, know, learn, etc.). And, as a rule, we don’t put a comma between a verb and its object. 

Examples of which with indirect or implied questions: 

• “She asked me which pair of shoes were mine.”
• “I honestly don’t know which paint colors he prefers for that room.”
• “I’m learning which native plants will thrive in our front garden beds.”

 In all of the above examples, you can use the subject and its verb to ask a question: 

• What did she ask me? (Answer: which pair of shoes… )
• What don’t I know? (Answer: which paint colors… )
• What am I learning? (Answer: which native plants… )

Since the answer to each of these questions is the direct object of the primary verb, we don’t put a comma before the “which.” 

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To illustrate this, let’s see how it looks when we put commas before other examples of direct objects: 

• She ate, the last cookie (and she wasn’t even sorry). 
• He ran, a mile before he realized he’d taken a wrong turn.
• The toddler grabbed, my earring and wouldn’t let go. 

That last one roughly illustrates how painful it is to see a comma between a verb and its object. It just doesn’t belong there.

You don’t pause between the verb and the direct object any more than you pause between a noun and its primary verb: 

• She, climbed the mountain. 
• He, confirmed our good opinion. 
• They, were not amused. 

When do you need a comma after which? 

The only time you’d need to put a comma after “which” is to set off a parenthetical phrase (also called an “aside”) — which is also not essential to the meaning of the sentence.

Here are some examples; 

• “He has some questions which, just so you know, are the same as mine.” 
• “She knows exactly which, of all the shoes in her closet, are best for an interview.” 
• “They don’t know which, if any, of her kids work full-time over the summer.”
• “She hasn’t yet heard my excuse, which, by the way, is a brilliant one.” 
• “I’ve heard all you have to say, which, you should know, is not helping your case.” 

As you can see, it’s possible to have a comma both before and after a which. In those last two examples, the nonrestrictive clause starting with “which” is non-essential. So is the parenthetical phrase that comes right after the which. 

You can hear the slight pauses in both places, right? It’s as if you’re signaling the reader to slow down a bit and listen for the sudden break in the flow of the sentence.

Sure, you could just scrap those pauses and strip the sentence to its essential elements. But while you wouldn’t sacrifice the meaning, you’d lose much of the sentence’s character. 

Character and commas often go together. 

Now you know how to answer the question, “When is there a comma – before or after which?” you can explain the rules to anyone who asks. 

It turns out the only time you really need a comma is when the “which” clause isn’t strictly necessary to the sentence. 

The comma is there to make reading easier.