Restrictive and Nonrestrictive Clauses

You will remember that one of our readers asked a question about the difference between these two sentences:

The old lady who was injured in the accident is now in the hospital.
The old lady who is now in the hospital was injured in the accident.

We discussed modifying clauses and their placement, but these two sentences give us a chance to talk about two specific kinds of modifying clauses: restrictive clauses and nonrestrictive clauses.

A restrictive clause identifies the noun or verb that precedes it and is needed to understand which person or thing is meant:

I preferred the soprano who sang last year.
The old lady who was injured in the accident is now in the hospital.

A nonrestrictive clause adds information about something but is not needed to understand which person or thing is meant:

My uncle, who I haven't seen in years, works for the government.
The old lady, who is now in the hospital, was injured in the accident.

As you can see, nonrestrictive clauses are separated from the rest of the sentence by one or two commas; restrictive clauses are not separated from the rest of the sentence by commas.

There are a few other interesting usage points when considering whether a clause is restrictive or nonrestrictive. Clauses that begin with which and refer to the entire main clause are nonrestrictive:

She ignored my advice, which surprised me.

When a restrictive clause begins with a relative pronoun or relative adverb, the pronoun or adverb can often be omitted:

The reason (that) he gave wasn't convincing.
That was the year (when) I went to Romania.

But this is never possible in nonrestrictive clauses, or in clauses where the pronoun is the subject:

CORRECT: He had a magazine, which he had finished reading.
INCORRECT: He had a magazine, he had finished reading.

CORRECT: They're the relatives who raised me.
INCORRECT: They're the relatives raised me.

In the two sentences we looked at last time, the first sentence ("The old lady who was injured in the accident is now in the hospital") uses a restrictive clause: there many be many old ladies in the hospital, but the one we are talking about now is the old lady who was injured in the accident. The second sentence ("The old lady, who is now in the hospital, was injured in the accident") uses a nonrestrictive clause: the main point of the sentence is that the old lady was injured--that she is in the hospital does not clarify which old lady we are talking about as there may be many old ladies at the hospital, but there is presumably only one old lady who was injured in the accident.