English Grammar Drills

Post-Noun Modifiers 63
1. By far the most important difference between them is the use of commas. Restrictive
adjective clauses are never set off with commas. Nonrestrictive adjective clauses are always set off
with commas. The difference in comma use is the only thing that absolutely defines which adjective
clauses are restrictive and which are nonrestrictive. This difference in comma use cannot be
overemphasized.
It is helpful to think of the restrictive modifier as part of the meaning of the antecedent noun.
Since the restrictive modifier is part of the meaning of the noun, the restrictive modifier can never
be separated from that noun by commas. Conversely, the pair of commas around a nonrestrictive
clause signal that the adjective clause is only loosely attached to the noun it modifies. Nonrestrictive
clauses are optional modifiers—they can be deleted without changing the basic meaning of
the nouns they modify.
2. The internal grammatical structures of restrictive and nonrestrictive clauses are identical
except (according to some writers) for the choice of whether to use that or which as the relative
pronoun. Some authorities (mostly authors of technical writing books) strongly advise that we
use that in restrictive clauses and which in nonrestrictive clauses. Notice that the two examples
above have followed this convention: the restrictive clause uses that and the nonrestrictive clause
uses which.
In actual fact, the behavior of native speakers is more complicated. It is indeed true that native
speakers use which in nonrestrictive clauses. Using that in nonrestrictive clauses is ungrammatical.
For example:
Nonrestrictive:
X Our house, that is on the corner of Elm and 17th Street, is
for sale.
The problem is that native speakers freely interchange that and which in restrictive clauses in
all but the most formal situations. For example:
Restrictive:
Restrictive:
Restrictive:
Restrictive:
Restrictive:
Restrictive:
Restrictive:
Restrictive:
The shirt that you bought for me has lost a button
The shirt which you bought for me has lost a button.
We gave the tickets to the people that were already in line.
We gave the tickets to the people which were already in line.
They reviewed the instructions that they had been given.
They reviewed the instructions which they had been given.
The car that had just passed us suddenly spun on the ice.
The car which had just passed us suddenly spun on the ice.