Grammar: Commas with Relative Clauses
That versus which perplexes a lot of people. First things first—let’s talk about restrictive versus nonrestrictive clauses. A relative clause is said to be restrictive if it provides information that is essential to the sentence. In these cases, that is the word you’ll want to use.
Let’s take a look at some examples.
• The door that is at the end of the hall is open.
• The bill that is due tomorrow is sitting on my desk.
• The toy that Bobby wants for his birthday is being held at the store for me until I can pick it up.
So, what do all of these mean in plain English? Basically that there are multiple items, and the reader needs that extra bit of information to identify the specific one we’re talking about.
• The door at the end of the hall (as opposed to the one on the right)
• The bill that is due tomorrow, not the ones that are due on the first of the month
• The toy that Bobby wants for his birthday, not some other toy
When would you use “which” then?
Basically anytime there is only one item, thus meaning that there is no possibility for confusion.
• The door, which is at the end of the hall, is open. (There’s only one door, and it’s at the end of the hall.)
• The bill, which is due tomorrow, is on my desk. (There are no other bills on my desk.)
• The toy, which Bobby wants for his birthday, is waiting at the store for me to pick up. (You’ll notice that this example doesn’t work very well. Why not? Because the likelihood that there’s only one toy at the store is very slim.)
A couple of notes about which versus that:
- Generally speaking, you can delete a nonrestrictive clause and the sentence is just fine. Because of this, they are offset by commas and can usually be removed from the sentence without damaging the clarity of your words.
- If “that” is unnecessary in a sentence, it can safely be omitted. For example:
The door that is at of the hall is open can safely be changed to The door at the end of the hall is open.
- And finally, a restrictive clause does not require a comma, whereas nonrestrictive clauses do. If you’re looking at your sentence and the comma looks wrong, you probably want that, and vice versa. This isn’t foolproof, but it’s a good quick check. 🙂
Additional information can be found in Chicago Manual of Style, 17th Edition, section 6.27 or Chicago Manual of Style, 16th Edition, section 6.22. Both versions are available as an online subscription. As always, do let me know if you have any questions. 🙂
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