That vs Which

One of the most common grammatical errors I see – and I see it EVERYWHERE – is the misuse of “that” and “which.” These words can be used similarly, but they are not, in fact, interchangeable. So let’s take a look at “that” and “which” and see if we can figure out how to use them correctly. So that vs which… which to choose?

While both “that” and “which” can be used in a variety of ways, I’m only talking about using them to lead into a descriptive phrase, or clause. No, I’m not talking about the fat guy in the red suit who comes around in December, but about essential and non-essential relative clauses.

Why am I talking about clauses, when I always promise I won’t get too grammar-y on you* Because this is an easy one, and understanding essential vs. non-essential clauses is the key to understanding that vs which.

Quick and easy definitions of clauses:

Relative clause

I’m not going to go too in-depth on this,* so just think of it this way: a relative clause is used with or within a complete sentence (which contains at least a subject and verb) to add detail.

Essential clause

Must be present in order for the sentence to make sense. Essential clauses always use “that” to introduce them.

Non-essential clause

Nice to have in the sentence, because it adds detail, but it’s not necessary and can easily be removed without changing or muddying the sentence’s meaning. Independent clauses always use “which” to introduce them.

That vs Which Clause Examples

That vs Which Essential Clause Example

“Hand me the book that is sitting on the table,” the librarian commanded.

This sentence uses an essential clause: “that is sitting on the table.” (Note the use of the word “that”!) Why is it essential? Because the librarian is probably surrounded by books, so the clause is necessary to be sure we know exactly which book the librarian wants. (And note that the “which” near the end of my previous sentence is being used in an entirely different way and has nothing to do with the topic at hand.)

That vs Which Non-Essential Clause Example

“This book, which has such a beautiful cover, is one of my favorites,” she said.

This time the clause is “which has such a beautiful cover.”

Sure, sure, you can argue that the reason this book is one of her favorites is because of the beautiful cover, but it’s not likely. Let’s try removing the clause.

“This book is one of my favorites,” she said.

See? Still works! The original example uses a non-essential clause: nice to have, but not necessary to the sentence. (Note the use of the word “which”!)

As you look at the examples, you may have noticed something else that sets “that” and “which” apart. I’ll give you a hint: it involves punctuation…

That vs Which The Comma

Yes! The comma! In situations where you’re using “that” or “which,” remember that you ONLY use a comma with “which.” It’s a quick way to let readers know that they’re heading into a non-essential clause. (Depending on the rest of your sentence, you may also need a comma at the end of the clause.)

If you have a comma with a “that,” your subconscious could be telling you that you’re dealing with a non-essential clause and you should use a “which” instead.

That vs Which The Comma Example (wrong)

I grabbed the book, that was overdue, and sprinted to the library.

Let’s break it down: First, is “that was overdue” an essential clause or a non-essential clause? Not sure? Let’s try taking it out of the sentence.

I grabbed the book and sprinted to the library.

Hmmm. This is grammatically correct. There’s nothing wrong with the sentence. But the two parts of the sentence – “I grabbed the book” and “sprinted to the library” – are no longer connected. We’ve lost some meaning by removing the clause. This sentence needs that clause so that the reader can fully understand. Therefore, it’s an essential clause and should indeed use “that.”

However, this example does have an error. Check out the punctuation around the clause. Do we need commas with an essential clause/”that”? Nope! Take off those commas!

That vs Which The Comma Example (correct)

I grabbed the book that was overdue and sprinted to the library.

So remember: if you can take the clause out of the sentence, and the sentence still makes sense, it’s a non-essential clause and needs a “which” and a comma (or two!). If you can’t take it out without changing or muddying the meaning of the sentence, it’s essential, so it needs a “that” and no commas!

*There are MANY ways to think about clauses and how they work in sentences. I have chosen to use this approach because I think it’s a quick and dirty way to help you make the correct grammatical choices. I apologize to all the grammar purists out there for not delving deeper into the term!

Does grammar make you feel nauseous… or is that nauseated?

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Rachel is a full-on, hardcore grammar freak. Her favorite punctuation marks are parentheses, em dashes, and ellipses. She still loves adverbs but is trying to wean herself off of them. And she truly believes that it’s okay to split an infinitive. In addition to her grammar obsession, Rachel writes light contemporary romance – occasionally with a paranormal twist – and is published in short fiction.