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Grammarology 2.0: That vs Which

This is the first Grammarology column for 2012. The column will run every few weeks. In the mean time, please, send in your grammar questions. Anything from the trivial to the profound is welcome. Comments are also very encouraged.

Q: Caleb Thompson wrote:

“When is it appropriate to use that as opposed to which?

AGenerally speaking, that can be used with integrated (restrictive) relative constructions (e.g., This is the one that broke), and which can be used with both integrated (e.g., This is the one which broke) and supplemental (non-restrictive) relatives (e.g., This group, which I’ve taught before, is a nice one).

Of course, as usual, there’s more to this than the above. The word that is a subordinator; it is not a relative word like who, where, when, or which. It’s the same that used in content clauses (“noun clauses”; e.g., He said that it was time to go.) This gives it the flexibility you see below. And, as a result, even in integrated relative clauses, that and which are not always interchangeable.

When the relative construction follows a fronted preposition, only relative words will do, so relative pronoun which is available, but that isn’t. (Remember the * means it’s ungrammatical.)

  • We have to protect the environment in which/*that we live.
  • No art can be properly understood apart from the culture of which/*that it is a part.

Conversely, when the relative clause is post-modifying superlatives, we can choose between that or no subordinator, but which is not possible:

  • He’s the best (that/*which) I’ve ever seen.
  • He’s the fastest runner (that/*which) I’ve ever seen.

Also in cleft sentences like the following where a prepositional phrase is being modified, only that is available.

  • It wasn’t for you that/*which I bought it.
  • It was before I moved here that/*which I met her.

Finally, which usually cannot be used where other relative words would work, but that typically can:

  • They gave the prize to the girl that/*which spoke first. [who]
  • He was to leave at the time that/*which she arrived. [when]
  • They looked every place that/*which she could be. [where]
  • That’s not the reason that/*which she resigned. [why]
  • I like the way that/*which she plays. [*how]

As you can see here, if that were a pronoun, it would be a pronoun that replaces not just nouns but almost everything under the rainbow. But if it’s a subordinator, it’s doing exactly what we’d expect.

Bonus material

Merriam-Webster’s Dictionary of English Usage has a good historical overview of the evolution of which and that in relative constructions. They call that a relative pronoun, and historically it may have been so. Now, however, it is a subordinator, as I said above. Other English subordinators include to (e.g., it’s hard to change), for (e.g., it’s hard for me to change), whether/if (e.g., I wonder whether I can change), and how (e.g., I don’t know how I can change).

[Correction added Dec 17, 2012: A previous version of this post erroneously claimed that which was unavailable in all cleft sentences. Thanks to John Anderson for pointing out the error!]

Grammarology 2.0 aims to take the discussion of grammar up a notch or two (your mileage may vary) and should appear about once every few weeks. It’s written by Brett Reynolds, who teaches EAP at Humber College and is just about as nerdy about grammar as you can get. He’s is always happy to take questions, which you can send to

Brett Reynolds teaches English in Humber's EAP program. (OK, who's fooling who with this third-person stuff?) I speak Japanese, remember a fair bit of French, and know something about a few other languages too. I'm crazy about grammar, and spend too much time online for my own good.

  • Tyson - January 9, 2012

    This is a very immediately useful point, Brett, which I’m sure many grammar teachers are happy to know rules for. Interesting though, I’ve never heard relative clauses referred to as “integrated” before. Restrictive or non, Defining or non, but never “integrated”.

    • Tyson - January 9, 2012

      Oh, that goes for “supplemental” too. 😉

  • Brett - January 9, 2012

    Thanks, Tyson! The problem with “restrictive” is that they aren’t always. The Cambridge Grammar of the English Language gives this example:

    She had two sons she could rely on for help, and hence was not unduly worried

    Here, the clause is integrated into the NP. It’s not supplemental. We can’t just leave it out. But if she only has two sons, in no way is it restrictive. So even though it’s less familiar, I think it’s more useful to think of it this way.

  • Nancy - January 10, 2012

    As a fairly new ESL supply teacher, I love teaching grammar, but I admit, this article has left me extremely befuddled. I’d never heard of cleft sentences or post-modifying superlatives or integrated relative constructions, and I feel like I had been comfortably treading water in a very small pond, but have now found myself dog-paddling in an unfamiliar ocean of grammatical confusion!

    However, with 30 years of Admin Assistant experience under my belt, one skill I have developed is that of proof-reader. There is one teensy little error in one of your paragraphs that came under my radar. I’ve capitalized the word in question.

    “As you can see here, if that were a pronoun, it would be a pronoun THE replaces not just nouns but almost everything under the rainbow. But if it’s a subordinator, it’s doing exactly what we’d expect.”


    A tiny typo, but it adds a little confusion to an otherwise already overwhelming work.

    • Brett - January 11, 2012

      Hi, Nancy, and thanks for the proofread! Fixed now.

      There’s nothing wrong with a bit befuddlement, as long as it’s not overwhelming. If you look at the examples, can you puzzle out one or two of the terms?

      • Nancy - January 11, 2012

        Ohhhh, “puzzle out” isn’t exactly the word. It’s more like “climbing Mt. Everest”. What I’ve realized is that, although I’ve always loved the study and teaching of grammar, I have miles to go before I can consider myself a good teacher. Your article just reminds me of that.

        • Tyson - January 12, 2012

          Being a good teacher isn’t determined by the amount of deep grammar understanding you have, Nancy. How you teach should be more functional than technical. This column is largely for people with a particular interest in the technical aspects of grammar, not a guide by which to teach.

          • Brett - January 15, 2012

            What Tyson said: being a good teacher doesn’t stand or fall on your knowing lots about grammar.

            There are a few terms here that you don’t know, but it’s not insurmountable. What, for example, do you think it would mean to post-modify something?

          • Nancy - January 15, 2012

            I have to reply on Tyson’s post because I can’t see a “reply” to click on, on Brett’s post. But I have to say with sadness that I had to google “post-modifier”. Once I read the description, it made sense to me, but it saddened me to have to google something I should already know!