Grammar 6 min read

Which vs. That: How to Choose the Correct Determiner

Even experienced writers struggle with some grammar rules. Knowing whether to use which or that is near the top of that list. Though you may think the two words are interchangeable — surprise! They’re not. We’ll break down the which vs. that debate and give you some examples to help you remember.

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Main Takeaways:

  • What refers to unlimited options while which refers to limited possibilities.
  • What vs. which deals with quantities rather than clauses.
  • Deciding whether to use which or that depends on whether it’s used in a defining or non-defining clause.
  • Use that in defining clauses that are essential to the sentence.
  • Opt for which in non-defining clauses that are not essential to the sentence.
  • Use the mnemonic “sandwich crusts aren’t essential” to remember that “which” and nonessentialon-defining clauses go together.
  • Commas often offset non-defining clauses.

Which vs. that. They seem like such small, simple words, but there is a right time and place for each. To avoid major grammar embarrassment (just kidding, we don’t judge!), check out our quick guide.

It’s easy to learn when to use which or that and the difference between the two. By the time you finish this article, you’ll be a which vs. that grammar guru.

What is the Difference Between Which and That?

This isn’t about nouns and verbs. Instead, it all comes down to what else is going on in your sentence. The quick answer is that we use that with defining clauses and which to introduce non-defining clauses. To understand things further, we need to get to the root of what those two clauses look like.

which vs. that: Choosing between
Choosing between “which” and “that” depends on the kind of clause your determiner will define. Use “which” for nonrestrictive clauses, and “that” for restrictive clauses.

Defining vs. Non-Defining Clauses

A defining clause is also known as an essential clause or a restrictive clause. That’s because it adds essential information to the sentence. We’re “restricted” from removing it from the sentence; without it, the meaning would change.

My dog that has bad breath needs to see a doggy dentist.

In this example, “that has bad breath” is a defining clause because it’s defining something about the dog. The writer may have several dogs, but he or she is specifically talking about the one that has bad breath. “That” is the right choice in this case.

A non-defining clause is also referred to as a nonessential clause or nonrestrictive clause. It’s not essential to the meaning of the sentence.

Therefore, you could remove it, and your sentence would still mean the same thing. You might lose some fun details or interesting “color” in the process, but the core meaning wouldn’t change.

Expert Tip: Some non-defining clauses are easy to spot because they’re offset by commas or parentheses.
Tara’s shoes, which she bought while on vacation, are bright green.

Tara’s shoes are bright green, whether we know that she bought them on vacation or not. That means which she bought while on vacation” is a nonrestrictive phrase, and which is the correct word to use.

That or Which: How to Remember the Difference

When you’re in a hurry, it’s easy to forget whether you should be using which or that. To help this concept stick, think of “which” as being disposable, just like the crust of a sandwich! (This will be especially easy to remember if you’ve ever been around a toddler.)

So, which/sandwich is disposable, meaning nonessential. We use which with nonrestrictive clauses.

I gave my little girl a sandwich, which she only ate part of.

On the other hand, that is necessary—that is the part of the sandwich we want to keep!

The sandwich that my daughter ate had no crust.

“That my daughter ate” is important because it explains which sandwich the author is talking about. That means it’s an essential or restrictive clause, so that is the correct word to use.

Which vs. That: How to use Them in a Sentence

There are many ways to use which or that in a sentence. The important thing is to be sure you’re using them correctly. That means sticking to which when you have a nonessential or nonrestrictive clause and using that for essential or restrictive clauses. If you’re not sure whether to use which vs. that, see which type of clause your sentence contains.

Cars that are hybrid use less fuel.

In this which vs. that example, we know that are hybrid” is an essential phrase. Without it, we’d be left with “cars use less fuel,” which has a different meaning. Since that are hybrid” is a restrictive clause, we’re right to introduce it using that.

I accidentally drove over a nail, which was left outside a construction site.

While it’s interesting to know where the author found the nail, it’s not essential. If you omit which was left outside a construction site,” the meaning of the sentence remains. Which is the right choice.

Sometimes you may see that or which paired with another introductory word. The same rules apply even if that or which follows a preposition, such as by, for, or on.

I found her strange, in that she didn’t make eye contact when she talked.
His writers, of which he had three, rarely delivered their work on time.
The action movie, in which the male lead saved the world, scored big at the box office.

How About What vs. Which?

What vs. which is a whole other ballgame. In general, we use what when we’re referring to an unknown quantity or endless possibilities. We use which when referring to a limited number of items, such as choosing between just two possibilities.

What did you have for dinner?

You could’ve eaten anything from pizza to sautéed snails. Using “what” reflects all those possibilities.

Which subject in school is your favorite?

That question refers to a limited number of subjects, so “which” is correct.

The same goes for:

Which route to the airport has the least amount of traffic?

You’re looking at the best of a few possible routes, so the possibilities are limited.

Sometimes you can use both what and which in the same sentence, but the meaning will change slightly.

What movies do you love?
Which movies do you love?

Given the phrasing of the first question, you could answer with any movie in the whole universe. If the author asked you the second question, he or she might be referring to two specific movies.

How do you feel about that vs. which now?

Read More: Affect Vs. Effect: How To Choose The Correct Word

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Krista Grace Morris

Krista heads up Marketing and Content Creation here at INK. From Linguistics and History to puns and memes, she's interested in the systems we create to share our ideas with each other.

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