Confusing the words ‘that’ and ‘which’ is a common grammar mistake - and easy to make. Let’s break down the context in which they’re used and how to use them correctly.
What is the difference between which and that?
The reason ‘which’ and ‘that’ are often confused is because they can both be used as relative pronouns. Relative pronouns are pronouns which introduce relative clauses. This means they introduce a dependent (relative) clause - one which can’t stand alone - to an independent clause, which makes sense by itself.
Although there are variations based on American and British English, typically ‘which’ is used to refer to animals and things, whereas ‘that’ is used to refer to people, animals and things.
This isn’t the only distinction, though. It also depends on whether you’re using a defining clause or a non-defining clause. In defining clauses, you should typically use ‘that’. In non-defining clauses, ‘which’ is accepted.
What’s a non-defining clause?
Grammarians generally advise that if you can remove a clause without removing meaning from the sentence, that clause is non-defining - disposable.
I like to think of a non-defining clause as Grandpa Simpson telling his long, rambling stories.
When Grandpa is showing an example of how to tell a story that doesn’t go anywhere, he often says, “which was the style at the time” as an aside. It’s a detail, but it’s not an essential detail, and the rest of the sentence doesn’t depend upon it to make sense.
So, if you’re wondering whether or not to use ‘which’, think of Grandpa.
What’s a defining clause?
You can probably guess that if ‘which’ is used for non-essential clauses, a defining clause is essential to the meaning of a sentence.
Let’s take a painfully predictable example (apologies):
The fox that is quick and brown jumps over the lazy dog.
The use of ‘that’ implies that there is not only one fox in the picture here, and we use the detail to differentiate it from the other foxes. This means it’s defining.
On the contrary:
The fox, which is quick and brown, jumps over the lazy dog.
Using ‘which’ in this sentence implies that the ‘quick and brown’ description of the fox is an additional detail, but that there’s only one fox in the picture. This means it’s non-defining.
Examples of that and which
- In spite of everything I shall rise again: I will take up my pencil, which I have forsaken in my great discouragement, and I will go on with my drawing.
— Vincent Van Gogh
- The books that the world calls immoral are books that show the world its own shame.
— Oscar Wilde
- Poetry is a mixture of common sense, which not all have, with an uncommon sense, which very few have.
— John Masefield
- To be yourself in a world that is constantly trying to make you something else is the greatest accomplishment.
— Ralph Waldo Emerson
‘That’ and ‘which’ mix-ups are a common mistake to make, but once you know what’s a Grandpa Simpson detail and what’s not, it’s easy to know what word to use. Thinking of your clauses in terms of ‘defining’ and ‘non-defining’ can help you make the distinction between these relative pronouns.
This is useful to know, but some other grammar ‘rules’ are only guidelines - check out our lists of grammar rules you shouldn’t take too seriously.