When to Use a Comma Which and Who

When to Use a Comma Before Which and Who

The rule for whether you should place a comma before which and who is the same. As with most rules about placing commas in sentences, they are intended to replicate speech patterns and make sentences clear; thus, you have some leeway, but the rules here are generally firm. In order to use these commas properly, you need to understand the difference between restrictive and non-restrictive clauses.

Restrictive Clauses

A restrictive clause is necessary for the meaning of the sentence. It is fully integrated into it and cannot be removed without losing the full meaning. When which or who introduces such a clause you should not use a comma.

The car which I am trying to fix should have ended in a trash heap. ✔
The car, which I am trying to fix, should have ended in a trash heap. ✘
The man who came to my door the other night was actually trying to sell me his junk car. ✔
The man, who came to my door the other night, was actually trying to sell me his junk car. ✘

Both the clauses which I am trying to fix and who came to my door the other night are clauses that are integral parts of the sentence, so you don’t need to put a comma before them. Think of it this way – if the which or who clauses define their antecedent (in our examples the car and the man) they are likely restrictive clauses and no comma is required.

You can use a simple test to determine whether which introduces a restrictive clause or not. If you can easily replace which with that, then it is a restrictive clause.

The game which I intend to buy should be coming out soon. ✔
The game that I intend to buy should be coming out soon. ✔

In general, it is preferred to use that instead of which, where appropriate. This is especially true if you are using American English.

Non-Restrictive Clauses

Non-restrictive clauses, on the other hand, provide additional information. They are supplementary clauses that can be removed and the structure of the sentence will remain the same. If you remove them, you lose some information, but the base meaning remains. When which or who introduces such clauses you should put a comma before them (and after).

Jake’s new car, which he bought only a week ago, is already breaking down. ✔
Jake’s new car which he bought only a week ago is already breaking down. ✘
The guy I met yesterday, who it turns out is wanted by the cops, tried to sell me an old car. ✔
The guy I met yesterday who it turns out is wanted by the cops tried to sell me an old car. ✘

The clauses which he bought only a week ago and who it turns out is wanted by the cops add information, but don’t define the meaning of the sentence. They can be removed and the structure of the sentence would remain intact. In such cases, use a comma both before which or who and at the end of the clause.

You can use the same test to check whether which introduces a non-restrictive clause. If you can’t comfortably substitute which with that, the clause is non-restrictive.

The game I bought, which came out a month ago, is boring. ✔
The game I bought, that came out a month ago, is boring. ✘
The game I bought that came out a month ago is boring. ✘

Comma Before Which and Who in Indirect Questions

When a sentence starts with either of these words, the answer is obvious – you don’t need a comma. There could be some confusion when they are used for indirect questions that are part of the sentence. In these cases, the rule is the same – no comma is needed.
I asked Yasmin who was coming. ✔
I asked Yasmin, who was coming. ✘
I asked Maya which items are on sale. ✔
I asked Maya, which items are on sale. ✘

The Short Rule Don’t use a comma before which and who when they are at the beginning of a restrictive clause.

The house which I plan to buy is really cheap. ✔
The woman who gave me a ride was really nice. ✔

Use a comma before which and who when they are at the beginning of a non-restrictive clause and at the end of the clause itself.

His house, which was built in 1808, needs serious repair. ✔
Jane’s new boyfriend, who she met at the theatre, is really stuck-up. ✔

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