One of the most overused words in the English language has to be the word that. Writers often make jokes about drastically lowering their word count simply by pulling out instances of that. And we here at Inkwell’s know that situation first-hand; we’ve spent hours pulling extraneous thats out of academic texts.

It’s well-established, then, that you don’t need as many thats as you think you do. But there’s another, more pressing issue for many writers: when the heck do you use which and when do you use that? If you’re trying to limit your use of that, it can be tempting to swap in which instead.

There is some surprising nuance to using that and which correctly, some of which actually depends on where you’re located on the globe. Let’s dig in.

That vs. Which: An Issue of Clauses

Here in Canada and in the United States, that is primarily used with what are known as restrictive clauses. These clauses cannot be separated from the sentence. They are integral to the meaning of the sentence.

By contrast, which is used with non-restrictive clauses. These are usually parts of the sentence that are closed off by commas. They aren’t so important to the sentence that you need to have the information they provide. You can think of them as a sort of “aside” or bonus. They’re often helpful information to have, but they are not strictly necessary.

This is often easier to see in action:

The plane, which was headed southeast, made an emergency landing in a field.

The plane that headed southeast made an emergency landing in a field.

Now, you might think these two sentences are simply giving the exact same information. To some degree, they are. In the first example, though, the information about where the plane was headed is enclosed in commas. It is a non-restrictive clause. The information given inside such a clause is not essential to the sentence.

So, in this case, we’re likely talking about a single plane. The direction it was heading is “additional” information.

In the second sentence, the directional information is a restrictive clause. That means it is essential to the sentence. In this case, we could be talking about many planes, so knowing which plane headed in which direction is crucial information. Without it, we may not be able to identify the right plane.

That vs Which Is All Contextual

Expanded context could help us see why the sentences are constructed this way:

On the morning of July 20, an Air Canada flight took off from the runway at Pearson International Airport. The flight didn’t get far. The plane, which was headed southeast, made an emergency landing in a field.

On the morning of July 20, disaster was narrowly avoided when two planes almost collided. Flight 343 took off from the runway and began its ascent, turning to the northwest. A second plane then entered the airspace. Both pilots reacted quickly; the plane that headed southeast made an emergency landing in a field. Emergency crews have been dispatched.

As you can see, that and which can tell us quite a bit!

Determining If a Clause Is Restrictive

Your next question is probably about how to determine if a clause is restrictive or not. As our examples noted, context is often a big clue. Are we talking about one particular thing? Is the information a key identifier?

Our favourite test for this is just popping the clause in question out of the sentence. If the sentence still makes perfect sense (and is grammatically complete), you have a non-restrictive clause! If the sentence no longer makes sense or feels incomplete, the information is likely essential (and you should put it back in).

Sometimes, punctuation can signal if a clause is restrictive or non-restrictive. If the clause is set off by commas, parentheses, or dashes, it’s likely non-restrictive. These punctuation marks, when they appear in pairs, signal non-restrictive clauses.

Be careful with this tip though! Not all writers use these marks correctly, especially not in the first draft. You may want to practice with some previously edited work. If you’re working on your own book, you can simply add the punctuation to see if it changes the meaning of your sentence.

That vs. Which around the Globe

If this difference between that and which seems unusual to you, it might be because you’re familiar with British usage. What we outlined above is predominant in North America, so most Americans and Canadians will follow this rule, even if they can’t articulate it.

British usage, by contrast, doesn’t differentiate between the use of that and which by types of clauses. In fact, in British English, you’re just as likely to find which as part of a restrictive clause as a non-restrictive clause.

That means you can rewrite our restrictive clause example as follows:

The plane which headed southeast made an emergency landing in a field.

To the North American ear, that might sound incorrect, but British English speakers are less likely to find fault with it. That means, when you’re reading a book that follows British rules, you’re not going to see all the instances of which set off by commas.

Making Allowances for Either Method

This can become a bit confusing, especially if you’re a North American working with people from other places around the globe. Especially in Europe, Africa, Australia, and the Middle East, “British” English is more common, so individuals from these areas may follow more British usage. (And for those of you elsewhere, you’ll probably be baffled by North Americans’ insistence on using that and which in particular ways.)

Here in Canada, we also mix usage. Some people, especially younger generations, tend to follow our southern neighbours. Older Canadians are more likely to follow British rules, which likely reflects Canada’s strong ties to Britain through most of the 20th century, as well as the lasting influence of British English in schools.

With the rise of the Internet and the export of American culture, some people are more exposed to American English. As a result, they begin to adopt more “American” usage. That’s certainly the case here in Canada, where those south of the border have influenced our English for centuries now. The influence of business and the Internet is very prevalent. In other parts of the world, people learning English as an additional language will likely pick up the “usage” they’re most exposed to—be that British or American.

Which Is Correct?

In all actual fact, there’s no reason to differentiate between that and which like North Americans do, other than it sounds right to us. In this context, the two words mean the same thing.

Switching over to British-style which usage could help North American writers reduce the instances of that in their writing. Since we struggle with that anyway, it might be a good thing!

Of course, that and which have many other functions in English. It’s one of the reasons there’s so much confusion about how to use these words. And it’s one of the reasons we have so many instances of that in our work!

Get the Assistance You Need

If you’re still having a bit of trouble sorting your thats and your whiches, then it might be time to get in touch with an editor! We know the ins and outs of using these words, so you can rest easy.