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Who That Which? Make it work

Do you know when to use that and when to use which? How about who? If not, you’re not alone. Since we, as writers, can’t exactly avoid these words, let’s take a look at how to make them work.


That is a versatile word. You can use that to identify and specify something (grammar term: determiner). You can use it to refer to the previous sentence, where you assume the reader remembers what he/she just read. But in this article, we’re going to focus on that being used as a relative pronoun to introduce relative clauses.

A clause is a group of words with subject and verb. A relative clause connects to the main clause and adds meaning. There are two types of relative clauses – essential and non-essential. If the clause is essential, it means that the meaning of the sentence changes significantly if you remove it. So, what does this have to do with that, you ask?

Use that to introduce an essential clause

That should always be used when you have an essential (restrictive, defining) clause to introduce and is never used with a comma. (In BrE/AusE, you can use which for the same purpose, but if you want to make it easy to keep that from which, I would personally recommend using the tips in this article, based on AmE grammar rules.)


“She took the path that led to the castle.”

Without adding the clause “that led to the castle”, the sentence is weak, only creating questions for the reader. What path did she take? Were there several paths to choose from? Where was she going?

“He walked into the house that had a red door.”

To identify which house he walked into, use that.


Which, like that, introduces relative clauses. However, this little word introduces non-essential clauses, and it always takes a comma. The comma separates the non-essential clause from the main clause, indicating that the information provided isn’t needed for the main clause to make sense.

Use which to introduce a non-essential clause


“The prince looked out over his kingdom, which appeared dark and gloomy without his princess by his side.”

If you skip out on the clause starting with which, the sentence still works, it’s just not that detailed. Note that which needs a comma to get it going.

“She held on tight to the bear he’d brought her, which had three buttons and a red nose.

Use which to introduce extra information that isn’t necessary for the sentence to make sense.


Who is a relative pronoun when used with a relative clause and refers only to people.

In BrE/AusE, who and that is sometimes used interchangeably. If you are writing a sentence where you have both a person and a thing that you want to refer back to, you could easily use that. Also, if you’re talking about a group of people as an entity, like a team, use that.

Use who when referring to people

Remember how I said that which is preceded by a comma and that isn’t? When you use who, the use of a comma depends on which word would have been used if the sentence had referenced a thing.


“In between the thorns, the prince spotted the princess who was walking through the garden.”

In this example, the relative clause is essential – we don’t know which princess he spots unless we define it. With an essential clause, we use that. That doesn’t take a comma, and so neither does who in this example.

“The princess studied the handsome prince, who had a mole on his upper lip.”

While interesting, it’s not essential that the reader knows the prince had a mole. Some readers might even prefer not to know that. That fact makes this a non-essential clause – meaning that we need a comma before who, just like we would need before which.

Grammar Infographic


In summary, use who in clauses that refer to people, that in clauses that we need to make a sentence make sense, and which in clauses where we learn extra information about the main clause. For a quick reference, pin our infographic, and check back soon for more grammar tips!


The Swede is a self-proclaimed nerd who buys books on grammar and editing all the time, and who signs up for night classes just to keep her English up-to-date. When reading, she will inevitably spot spelling, grammar or syntax mistakes. If she’s reading a paperback, she’ll pull out a red pen and correct the error on the spot. Luckily, she mostly reads on her Kindle or she’d be buying red pens in bulk.

#sheilaandswede #editingandgrammar #amediting #grammar #amwriting

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