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?“
A: Generally 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.
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 firstname.lastname@example.org.