EDITING 101: 34 – When to use “which” or “that”?

When to use “which” or “that”?

This is a grammar conundrum which is specific to the US, and that confused me for quite some time myself. If you’re in the UK or elsewhere that uses UK style, you probably don’t even need to read this post, as it will simply confuse you. Just keep doing what you’re doing and you’ll be fine.

For all you United States writers, heads up and pay attention!

Many people feel “which” and “that” are interchangeable. I used to think so, too, until I did some research and discovered there is indeed a difference. The usage difference stems from whether or not the information following which/that is necessary to the sentence (nonrestrictive) or unnecessary (restrictive). (I don’t like the terms nonrestrictive and restrictive, because to me they are backwards and I get them mixed up. So I’ll stick to necessary or unnecessary, which are more understandable.) If the clause following which/that is unnecessary to the sentence structure, then you surround it with commas and use “which.” If it’s necessary to the sentence, you don’t offset it with commas and you use “that.”

For example:

  • This difficult subject is one that is taught in our school.

This is correct, because the phrase or clause “that is taught in our school” is necessary to the sentence. It could not be removed from the sentence without it rendering the sentence grammatically incorrect. It doesn’t need to be set off with commas, and the use of “that” is appropriate.

If you wanted to use “which,” you’d have to rework it this way:

  • This subject, which is one taught in our school, is difficult.

In this example, the phrase “which is taught in our school” is unnecessary to the sentence structure. Therefore, it is surrounded by commas and you use the word “which.” You could remove the clause (not Claus!) and be left with “This subject is difficult,” which is grammatically correct and a full, complete sentence in itself.

Don’t confuse information that is necessary to your story with information that is necessary to the sentence structure! 🙂

For the rule we’ve just discussed, what do you think of these sentences?

  1. The dog that was black barked incessantly all day.

  2. I wanted to climb the tree which is over there.

  3. My computer, that used to be Robert’s, is now broken.

  4. My bathroom which was recently redone is now blue.

Next week we’ll discuss ‘Using the five senses’

To see the index and catch up with missed episodes of this series – CLICK HERE


This series is not meant to be (nor will it be) simple static information.

I’ll be here for each post to answer questions, offer suggestions as necessary, and interact with you.

If there’s something you specifically want (or need!) to see addressed in terms of self-editing, please let me know in the comments under this, or any of the articles of the series.





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54 thoughts on “EDITING 101: 34 – When to use “which” or “that”?

  1. Even though I live in the UK I do want to thank you for another useful and thought provoking article Susan- it does make a lot of sense when you start to think about usage along the lines you pointed out (Notice the very clever avoidance of the conundrum …that you pointed out… which you pointed out.. Hey good on me for lazy writing!)

    Let’s go for that you pointed out… Now, do I get a gold star teacher?

    Seriously I always enjoy your articles They are damn good reading.

    Liked by 2 people

  2. 🙂 I remember past discussions with Susan on the subject. If restrictive and non-restrictive confuses you, you can also think in terms of “part” and “whole.”

    “That” is to be used to give information about the subject as a whole, while “which” is when you need to specify/highlight a “part” of the subject and separate it from the rest.

    Liked by 2 people

  3. So, in other words, it is best to rework the sentence and not use “which” at all. If it is unneeded in the sentence structure, why include it? That first sentence, in particular, bothered me. Why not simply say, “The black dog barked incessantly all day.” Is this correct,, or am I missing something?

    Liked by 2 people

    • “The dog that was black barked incessantly all day” means that there are multiple dogs present, but it’s specifically the black one which was barking. You could also tag on something like, “The dog that was black barked incessantly all day, but the dog that was white was silent.” However, it’s not really necessary to do that, as you’ve already specified it’s the black dog barking.

      “The dog, which was black, barked incessantly all day” is a way of imparting information to the reader which isn’t necessarily vital to what’s happening, but can help to improve visualisation/immersion. In this case, there’s only one dog present, but the fact that it’s black is added info. “The dog, which was big, black, and foamed at the mouth, barked incessantly all day” is also info not vital to the plot, but provides richer imagery and can alter the way the reader visualises the scene.


      Liked by 2 people

      • What The Urban Spaceman said. 😀 “Unnecessary” only refers to grammatically, not to the story line! A which clause can add important story information but still be unnecessary to the sentence structure.

        When I took my SATs that day, which was also the day the murders started, I had no idea what would come next.

        The sentence itself is fine without the which clause:

        When I took my SATs that day, I had no idea what would come next.

        “Which was also the day the murders started” is unnecessary to the sentence, but may be vital to the plot! 🙂

        Liked by 1 person


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