We have seen that you should be careful about several
possible types of errors with adjective clauses. Here
are two more things to avoid:

1. Be careful with punctuation. Do not use commas
with restrictive adjective clauses.

Some adjective clauses give information which is
necessary in specifically identifying nouns. These
clauses are restrictive. Other adjective clauses give
information which provides extra information, but
which is not necessary in specifically identifying
nouns. These clauses are nonrestrictive.

Use commas with nonrestrictive adjective clauses.
Do not use commas with restrictive adjective clauses.

Examples

Do you know the *pages, which we're supposed to
read tonight?

wrong: The adjective clause is needed
to show which pages are being talked
about. A comma should not be used.

Do you know the pages which we're supposed to
read tonight? (right)

___________________________________________

Joe has a *watch, which once belonged to
his grandfather.

wrong: The adjective clause is needed
to show which watch is being talked
about. A comma should not be used.

Joe has a watch which once belonged to
his grandfather. (right)

___________________________________________

Dr. *Schnabel who teaches my physics class
was born in Germany.

wrong: The adjective clause is not
needed to show which person is being
talked about because the name makes
this clear. Two commas should be used.

Dr. Schnabel, who teaches my physics class,
was born in Germany. (right)

___________________________________________

Bob's *wife who is a nurse is named Gloria.

wrong: Because Bob has only one
wife, the information is extra. Here,
a comma should be used.

Bob's wife, who is a nurse, is named Gloria. (right)

___________________________________________

Bob's sister who is a nurse is named Angie.

right: If Bob has more than one sister,
this sentence is correct.

Bob's sister, who is a nurse, is named Angie.

right: If Bob has only one sister,
this sentence is correct.

___________________________________________

2. Do not use that in nonrestrictive adjective
clauses. Instead, use which.

In restrictive adjective clauses, both that and who can
be used to refer to people, and both that and which
can be used to refer to things. This is not true for
nonrestrictive adjective clauses, however: that cannot
be used. Instead, use who or which.

Examples

The professor who teaches my physics class
was born in Germany. (right)

The professor that teaches my physics class
was born in Germany. (right)

Dr. *Schnabel, that teaches my physics class,
was born in Germany. (wrong)

Dr. Schnabel, who teaches my physics class,
was born in Germany. (right)

___________________________________________< /P>

Gerunds are verbs which are used as nouns. (right)

Gerunds are verbs that are used as nouns. (right)

Gerunds, that are verbs which are used as nouns,
end in -ing. (wrong)

Gerunds, that are verbs that are used as nouns,
end in -ing. (wrong)

Gerunds, which are verbs that are used as nouns,
end in -ing. (right)

Gerunds, which are verbs which are used as nouns,
end in -ing. (right)

Note: The second which in the sentence above is
correct but awkward; for variety, that should be
used instead