Relative clauses are also classified depending on their relationship with
the noun they modify. A restrictive relative pronoun identifies its
noun--and divides the world into categories. Look at our book example: The
book that my sister recommended was quite useful. The relative clause
points to a particular book--and also means that there are books that my sister
did not recommend.
A non-restrictive relative clause is used to give additional information
about the noun but not to identify it or to create categories. Look at
this example:
The Longman Student Grammar of Spoken and Written English, which was
published in 2002, is based on the Longman Grammar of Spoken and Written
English.
The relative clause--which was published in 2002--gives additional
information about the book but it doesn't say that there are two Student
Grammars--one published in 2002 and another at some other date.
Let's try this definition again by analyzing these two sentences. How
many groups of students is each sentence talking about?
1. The
students who turned their papers in early went to a party.
2. The students, who want to teach ESL/EFL, try to get a lot of
classroom experience.
What do you
think? #1--there are two groups of students. Those who turned in
their papers early and those who didn't. So, the relative clause in #1 is a
restrictive relative clause.
#2--that's about all of the students. It's non-restrictive. Notice
that the old definition about non-restrictives adding unimportant information
is not true. It's even silly. Why would you provide un-important
information?! A non-restrictive provides information that the writer
wants you to have but it is attached to a noun that is already identified and
doesn't need anything else to make you know which one you are talking about.
Probably for teaching purposes, the clearest examples of non-restrictive relative
clauses are those that go with proper nouns:
Douglas
Biber, who is a well-known corpus linguist, teaches at the University of
Northern Arizona.
At TESOL, I attended a lecture by Diane Larsen-Freeman, who is one of the
co-authors of the Grammar Book.
Better
examples for use in our ESL/EFL classes would be something from a textbook they
are using like this example I found in my sociology source:
A classic
example of an early woman sociologist is Harriet Martineau (1802-1876), who was
born into a wealthy English family.
This non-restrictive relative clause
gives important information that adds to our understanding of Harriet Martineau
but is not needed to define who she was.
