I get lots of reader queries about that and which. Here’s a typical email:
“I’m pretty good at grammar and usage, but apparently I don’t have a clue about the correct use of which and that. There’s some principle at work here that I don’t understand. Can you help?”
There is indeed a principle at work here, and it eludes many, including (and sometimes especially) the highly educated. However, I can make a comforting promise: Once we “get” that and which, we’ll never again have trouble with those words.
The whole matter rests on whether a given clause is restrictive or nonrestrictive. (Use that with restrictive clauses, and which with nonrestrictive clauses.) Here’s what we mean by restrictive and nonrestrictive:
If the content of a that or which clause could not be omitted without altering the sentence’s basic sense, the clause is restrictive and will therefore use that. Its content is not parenthetical or simply added information. Rather, it is essential information:
• The picture that hung in my study was damaged in the flood.
“That hung in my study” is restrictive. It restricts because it identifies or defines — we’re referring to this picture and this picture alone. The clause is therefore essential to the sentence because its purpose is to say which picture was damaged.
Notice, too, that no comma adorns the that clause. The picture, that hung in my study is not only incorrectly punctuated, it also shows how integral and organic the restrictive clause is. It doesn’t want to be separated from the sentence even by a comma.
How might this clause look if it were nonrestrictive? It would begin with which and would be enclosed in commas:
• The picture, which hung in my study, was damaged in the flood.
Notice that the nonrestrictive clause could be parenthetical and could also be omitted without altering the sentence’s main sense (which is that the picture was damaged in the flood).
• The librarian said she would destroy all the books that were damaged in the flood.
This shows another that clause and is therefore restrictive. It tells us that some books were damaged in the flood, and only those would be destroyed. Its content is essential, and if it were omitted, the sentence’s meaning would be altered — it would mean all the books would be destroyed.
•The librarian said she would destroy all the books, which were damaged in the flood.
This example shows a nonrestrictive clause. It tells us that all the books would be destroyed and offers the additional information that all were damaged in the flood. If we omit the which clause, the sentence’s main meaning is not altered — it still means that all the books would be destroyed. Note that which is preceded by a comma.
Examine the following. Restrictive or nonrestrictive?
• He was wearing the suit which he’d worn to his wedding.
• The garden which surrounded the place made it special.
• The diamond ring which had always adorned her finger was missing.
• Foods which have the lowest glycemic index are best for diabetics.
All those examples are wrong as presented. Why? They are all restrictive and need that, not which:
• He was wearing the suit that he’d worn to his wedding.
• The garden that surrounded the place made it special.
• The diamond ring that had always adorned her finger was missing.
• Foods that have the lowest glycemic index are best for diabetics.
It’s worth remarking that while we seldom see that errors, which errors abound. This observation underscores two points: Not only are we more confused about which than we are about that, but we also tend to overuse which in writing because we consider it more stately or learned than that. There’s no support for that assumption, however, and we should give it up.
Another stray point worth making: British writers often don’t observe the grammatical distinctions between that and which. But as we’ve seen, those distinctions matter.
So let’s do ourselves and our readers a favor and go on a which hunt.
Paula LaRocque is author of five books, among them “The Book on Writing.” Her latest fiction is a mystery novel, “Monkey See,” available on Amazon.com. Email: firstname.lastname@example.org. Blog and website: paulalarocque.com