Let’s see: when was my last
rant educational post about spelling or punctuation or usage? I think it’s time for another, and today’s is about restrictive clauses and non-restrictive clauses. Or to put it more simply, it’s about whether or not to stick commas in certain places.
A restrictive clause is a clause that’s necessary in order to determine which thing a sentence is talking about — it restricts the set of possibilities to a particular item or subset. Consider this:
The car that I bought in 1976 was yellow.I’ve bought four cars in my life. The restrictive clause, “that I bought in 1976”, tells you which of the four I’m talking about. But here, since we know we’re talking about cars I’ve owned:
My Datsun B210, which I bought in 1976, was yellow.This tells you that I’ve only bought one Datsun B210, in 1976. This time, “which I bought in 1976” is a non-restrictive clause. It adds information, perhaps useful information, maybe very important information. Yet, you could remove it, and you’d still know which car I’m talking about — the Datsun B210.
Now, note something about how the clauses are written into the sentence. The restrictive clause is introduced by “that”. The non-restrictive clause is introduced by “which”, and, more importantly, is set off by commas. We’ll look at both of those points.
First, the commas: non-restrictive clauses are set off by commas. Restrictive clauses are not. Remember it this way, perhaps: if I could remove it from the sentence and the item I’m talking about would still be well defined, put in the commas (it’s non-restrictive). Otherwise, no commas. That doesn’t mean you’d want to remove the clause; it might be critical information, but it’s still non-restrictive.
Here’s a good example: I have a friend with three siblings, called Alice, Greg, and Larry. My friend can correctly say these three things:
Because there’s only one sister, her name, in the first sentence, is a non-restrictive clause. So we put in the commas. The names of the brothers, on the other hand, are restrictive. Without them, you wouldn’t know the scientist from the vegetable hater. No commas.
My sister, Alice, lives in California.
My brother Greg is a scientist.
My brother Larry doesn’t like vegetables.
But if she said, “My sister Alice lives in California,” you might be inclined to ask about her other sisters. I sometimes jokingly do that when someone talks about “my wife Jane.” I’ll say, “As opposed to your other wife, Carol?” For some reason, people don’t seem to find that as funny as I do. Go figure.
And note that there are two commas, always, unless it ends the sentence (think of the closing period as eating the second comma). One could say, “I’m going to visit my sister, Alice.” One would never say, “My sister, Alice lives in California.”
The other thing we noted was the use of the pronoun “that” to introduce a restrictive clause, and “which” to introduce a non-restrictive one. That’s the customary usage, and many editors will insist on it. And the use of “which” (or “who” or “whom”, in cases of people) is required for non-restrictive clauses; I can’t say, “My Datsun B210, that I bought in 1976, was yellow.” That’s always considered wrong.
On the other hand, “The car which I bought in 1976 was yellow,” is not considered wrong (though it does look odd to me, and to others who are picky about this point). “Which/who/whom” can be used in restrictive clauses, but “that” is preferred in most cases. It’s good to switch to “which” in a sentence that would otherwise have too many “thats”, and necessary to switch if the clause is introduced by a preposition. Of course, the rule about when to use commas doesn’t change, even when we switch to “which”:
The car in which I drove to college was a yellow Datsun B210. [restrictive]
My Datsun B210, in which I drove to college, was yellow. [non-restrictive]
 I wanted a 240Z, but, well....