Who Needs a Comma

Commas can change the meaning of a sentence. This is the most important reason to use commas correctly. If you know when to use commas and when to leave them out, you help readers know what you mean. A good example of this is commas with the word Who

When to Use Commas with Who

 The word who can be used to introduce a non-restrictive clause. And like all non-restrictive clauses, non-restrictive clauses starting with who need to be separated from the rest of the sentence with commas. (Zen Comma Rule U: Use commas to separate non-restrictive phrases and clauses starting with who.)

 (A non-restrictive clause does not tell the reader which person you’re writing about. Rather, it provides an additional description of that person.)

 For example, if you’re writing about your father and you want to describe his eating habits, you can write this:

My father, who always enjoyed desserts after a large supper, was a large man.

For another example, if you’re writing about Batman in The Dark Night Rises and you want to describe his outfit, you can write this:

The Dark Night, who can be recognized by his black leather costume, fights Bane in a final showdown.

In the first example, the clause who always enjoyed desserts after a large supper provides a description of My father. This clause doesn’t tell whom you’re writing about. Rather, it provides a description. Like all non-restrictive clauses, it can be removed from the sentence without losing the main point, which is a good indication that it needs to be separated from the sentence with commas.

In the second example, you’re not telling the reader which Batman you’re writing about. Rather, you are providing a description of Batman with the non-restrictive clause who can be recognized by his black leather costume.

As you can see from these two correct examples, non-restrictive phrases starting with who are separated from the rest of the sentence with commas.

When to Leave Out Commas with Who

The word who can also be used to start a restrictive clause. And like all restrictive clauses, restrictive clauses starting with who are not separated from the rest of the sentence with commas. (Zen Comma Rule V: Don’t use commas to separate restrictive phrases and clauses starting with who.)

(A restrictive clause does tell the reader which person you’re writing about. It provides information necessary to understand the sentence)

For example, if you’re writing about your father and want to tell what kind of man he is, you might write this:

My father is a man who enjoys dessert after supper.

For another example, if you’re writing about the “good guys” in The Dark Knight Rises, you might write this:

The hero who fights the villain Bane is none other than Batman.

In the first example, you are distinguishing your father from other types of men. You’re answering the question “Which man?” The restrictive clause who enjoyed dessert after supper is necessary information to restrict the meaning of man to focus on your father. This is necessary information for understanding the sentence and is not separated from the rest of the sentence with commas.

In the second example, the restrictive clause who fights the villain Bane is necessary information to tell which hero you’re describing. The restrictive clause restricts the meaning of hero to focus only on the hero who fights the villain Bane.

How Comma Can Change the Meaning of the Sentence

As we see, those commas indicate a non-restrictive clause, and their absence indicates a restrictive clause. Now that we’ve discussed the difference between restrictive and non-restrictive clauses with who, let’s looks at an example where the commas change the meaning of the sentence.

If you’re writing about your sister, you can write

My sister, who has a PhD, is very smart

or

My sister who has a PhD is very smart.

In the first option, you have only one sister, and she has a PhD. You don’t need to tell the reader which sister you’re describing because you only have one. As such, the clause who has a PhD doesn’t restrict the definition of sister, and you need to separate the clause from the sentence with commas. The commas, which indicate a non-restrictive clause, tell the reader that you have only one sister.

In the second option, you have more than one sister, but you’re only writing about the sister with the PhD. Because you have more than one sister, you need to tell the reader which sister you’re writing about. The clause who has a PhD is necessary information and is not separated from the sentence with commas. The absence of commas, which indicates a restrictive clause, tells the reader that you have more than one sister.

Here’s your task. Ask yourself whether you are providing additional information or indicating which person. If you’re only providing additional information (non-restrictive clause with who), you need commas. If you’re providing information to indicate which person (restrictive clause with who), you don’t need commas.


Need help with commas? Get Zen Comma, an instructive reference guide on the 17 major uses and misuses of commas, available in PDF and Kindle formats. Read more about Zen Comma.

Your Writing Companion: Our e-book with samples from each of our writing guides: Get the free e-book (PDF, 45 pages) or purchase the Kindle version ($0.99).

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