That and which are so similar to each other, it’s tricky to know which one to use. It’s one of those grammatical situations where we know there’s a right way to it, we just don’t know what the right way is.
Fortunately, there’s a simple rule you can keep in mind when writing that can help you decide if you should use that or which.
Should I use that or which?
To know if you should use which or that, you need to know if the phrase containing the word is essential to the overall sentence.
We use which when it sits within a dependent or parenthetical clause, and we use that when it’s an in a dependent clause and is an integral part of the sentence.
The easiest way to understand the difference is with examples.
The building that has a green roof is for sale.
The content that follows that is essential to the overall sentiment.
On the other hand, you should use which if the information following is not strictly essential. For example:
The building, which has a green roof, is for sale.
But these two sentences aren’t equal.
The first example is specifying which building the speaker is talking about. The second is assuming we know which building the speaker is talking about and giving us some extra information, just because it can.
You have to know what information is essential when you choose that or which in your sentences.
More examples of that vs. which
Consider the following examples:
The book, which has a leather cover, is sitting on the top shelf.
The book that has a leather cover is sitting on the top shelf.
There’s a difference here.
The first example acts as if there’s only one book in question. The listener must know which book the speaker is talking about.
The second example specifies the book the speaker is talking about. There are other books, and the one that has a leather cover is on the top shelf.
There may be a right or wrong choice for this sentence, depending on the information you want to convey.
Let’s try another:
The plant that is growing by the window is really enjoying the afternoon sunlight.
The plant, which is growing by the window, is really enjoying the afternoon sunlight.
Again, we can see that the sentence using that is more restrictive and specific. The speaker is talking about the plant that is by the window.
In the sentence using which, the speaker is also talking about the plant by the window – but of course they are. There’s no other plant they could be talking about; they’re just letting us know that it’s by the window.
Independent clauses, dependent clauses and parentheticals
For anyone unfamiliar with these terms and how they relate to that and which, let’s delve into them for a moment.
Independent clauses (or when you can use that)
An independent clause is a complete phrase that can stand on its own. ‘I like to eat ice cream’ is an example of an independent clause. It’s a complete thought.
If you wanted to indicate that you wanted to eat strawberry ice cream, you might say, ‘I would like to eat the ice cream that is pink.’
You could even tell someone that your strawberry ice cream tastes delicious: ‘The ice cream that is pink is really yummy!’
But this sentence feels a little off. You could rearrange it to something like ‘The pink ice cream is really yummy’, or you could make half the phrase a dependent clause.
Dependent clauses (or when you can use which)
A sentence that might feel more natural could be something like ‘The ice cream, which is pink, is really yummy!’ This gives the sentence a different rhythm.
You can feel the way you would say this sentence and the different emphasis you would give to each part of it. That’s because ‘which is pink’ is now a dependent clause.
‘The ice cream […] is really yummy’ can exist without the clause in the middle if it wants to. It’s independent. But ‘which is really yummy’ depends on the rest of the sentence entirely.
It’s worth noting that there are plenty of other types of dependent clauses that don’t relate to that vs. which.
Parenthetical phrases/parentheticals
A lot of us are familiar with parentheses – these symbols: ( ). The content that sits within them is a parenthetical phrase, or simply ‘parenthetical’.
When a sentence says ‘The colour green (blue mixed with yellow) has strong connotations to nature’, we know that the content in the parentheses is addition information, but not essential.
We also know that because of this, we would use which in parentheses, not that.
Something to watch out for with parenthetical phrases is that we don’t always use parentheses to mark them. You could write the exact same sentence above and replace the parentheses with commas or em dashes.
‘…green, blue mixed with yellow, has strong…’ and ‘…green – blue mixed with yellow – has strong…’ are both valid forms of punctuation.
And in all of these forms, we would use which, because these examples are all still dependent on the rest of the sentence.
For instance, we’d write ‘Satay (which has strong peanut flavours) is delicious’, but never ‘Satay (that has strong peanut flavours) is delicious’.
The word that does not work in parenthetical phrases.
So… should I use which or that?
Hopefully by this point you’re bursting with knowledge about sentence structure, clauses, and when you should use that or which.
An easy way to check which word you should use is to see if you could cut out the clause it sits in.
If you can remove the clause completely without affecting the sentence’s validity, use which. If removing the clause would turn the sentence into a nonsensical fragment, use that.
Test yourself
The best way to learn any skill is to put it to practice. Try choosing the right answer for the following statements:
- The picture which/that depicts my favourite Pokémon is my desktop background.
- My mailbox which/that is bright blue is full of unread mail.
- The album which/that comes out tomorrow is going to totally change image!
Answers:
1. The picture that depicts my favourite Pokémon is my desktop background.
It wouldn’t really make sense to say ‘The picture, which depicts my favourite Pokémon, is my desktop background,’ because we have no idea what picture the speaker is talking about.
They need to specify that it’s the picture of their favourite Pokémon.
2. My mailbox, which is bright blue, is full of unread mail.
The colour of the mailbox is additional information and not essential to understanding the sentence. ‘My mailbox that is bright blue is full of unread mail’ doesn’t work.
3. The album that comes out tomorrow is going to totally change our image AND The album, which comes out tomorrow, is going to totally change our image.
Either of these sentences is fine! It just depends on what you want to prioritise in your text.
If you find yourself stuck while writing, you can always test yourself again to make sure you’re using the right word.
Does it sit in a dependent clause? Which. Is it within the main sentence/independent clause? That.
Knowing if you should use that or which isn’t complicated once you get a handle on it.