That vs. Which

May 4, 2023

Blue picture of the Milky Way. Photo by Felix Mittermeier on
Milky Way

First and foremost, May the 4th be with you 🙂

Maybe I’ll finally start Bad Batch today…

Anywho, on to the topic at hand – that vs. which.

Did you know that some style guides are specific about when you can use “that” or “which”? In UK English, it doesn’t always matter, but US English is pickier, especially when using something like The Chicago Manual of Style.

So, what’s the rule of thumb?

Let’s look at this sentence: “The bag, that had Star Wars patches on it, was on the ground.”

This isn’t quite right. But why?

In a sentence like this, the commas indicate that the information between them isn’t actually important – it’s just bonus stuff. Take out “that had Star Wars patches on it” and the meaning of the sentence wouldn’t change. Because it’s not needed, we actually use “which” instead of “that.” “Which” is another indicator that the information isn’t needed!

But what if there are multiple bags, and you need to specify which bag it is?

The information about the Star Wars patches is now vital to the meaning – without it, we wouldn’t know which bag was being talked about. Since that detail is necessary, the commas – which indicate the ability to be removed – can’t be there. “That” is also used instead of “which,” to further indicate the necessity of the detail.

So unnecessary, removable detail = “The bag, which had Star Wars patches on it, was on the ground.” Necessary detail = “The bag that had Star Wars patches on it was on the ground.” In UK English, you could rewrite the necessary sentence as ““The bag which had Star Wars patches on it was on the ground.” But note that the original sentence I wrote is incorrect in both cases.

TL;DR: Necessary information takes “that,” unnecessary takes “which.”

It’s something that I consciously have to make an effort to look for – I often follow UK convention when writing informally and personally – but it’s something you get used to. If you’re following US convention, I’ll be sure to help you find those pesky words!

Which style of “that vs. which” do you prefer/use? US or UK?

Published by Kaila Desjardins

Freelance editor, fiction writer, proud nerd.

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