Comma Usage: Restrictive vs. Nonrestrictive Relative Clauses

by Tina Blue
July 8, 2005

       In "Who, That, Which" I explain which of these pronouns are appropriate for different kinds of antecedents.  But another problem people often have when using relative pronouns is deciding when a relative clause is restrictive or nonrestrictive.

      Whether a relative clause is restrictive or nonrestrictive matters for two reasons:

                  1. Restrictive relative clauses are not set off by commas, while                                   nonrestrictive relative clauses are.

                  2. As a general rule, the pronoun "that" should be used for                                         restrictive relative clauses, and "which" should be used for                                    nonrestrictive relative clauses.*

       In "The Loyal Apposition" I offer clear guidelines for determining whether an appositive is restrictive or nonrestrictive.  These guidelines are equally valid for identifying restrictive and nonrestrictive relative clauses.


         If a relative clause adds parenthetical, nondefining, information, it is nonrestrictive.  A nonrestrictive (parenthetical) element is set off by commas, as in these examples.

                  ~Mr. Smith, who is a well-respected lawyer, has just                                 retired from active practice.

                   ~Professor James, who is an expert in Victorian poetry,                          will be giving a lecture tonight.


         ~Your task, which is to seek out new civilizations and boldly                 go where no man has gone before, will probably occupy the                 rest of your adult life.

      ~The U.N. Secretary General, who is named Kofi Annan, has                 spent much of his tenure working to promote peace in the Third                  World.

      ~This is Jennifer, who is my college roommate's youngest                     daughter.

      ~That book, which is the novel I was reading last week, is the                one I meant for you to take to the beach with you.



1.  When the relative clause limits or restricts the noun or noun substitute (substantive) it modifies, it is restrictive, and it is not set off by commas.

                   ~My brother that lives in Arizona is named Pat.

         In this sentence the clause "that lives in Arizona" is needed to specify which brother, since the reader has no other way of knowing how many brothers the writer has or which brother is being referred to.  (One way to think of the issue of restrictive and non-restrictive elements is that a restrictive element provides information that is necessary to narrow the field of candidates down to one.)

         But check out this example:

                ~My other brother, who lives in Texas, is named Sam.

In this sentence the first substantive, the noun phrase "My other brother," conveys the information that the writer has only two brothers, and it also specifies which of those two brothers is being referred to, so the brother's actual name is extra information--not necessary for specifying which of two brothers is being referred to.

         In fact, if the relative clause "who lives in Texas" were treated as restrictive, then the sentence would convey the information that the writer has two brothers named who live in Texas, and that would only make sense if another brother living in Texas had already been mentioned:

         ~I have two brothers that live in Texas. One is named Eric. My                     other brother who lives in Texas is named Sam.


              ~My sister, who is even deafer than I am, is named Linda.

        In this example, the information that Linda "is even deafer than I am" is extra. Since the main clause names the sister as Linda, the information in the relative clause is not necessary to identify which of the writer's sisters he or she is referring to.

               ~My youngest sister, who has three children, is named Carol.

         In this example, the phrase "my youngest sister" doesn't tell exactly how many sisters I have (though it does indicate three or more, because "youngest" is in the superlative form).  But it does specify exactly which one I am referring to, as there can be only one "youngest sister," so the information about the three children is extra information, not needed to specify which one of however many sisters I am referring to.

~My sister who has three children is the one I will be visiting   this summer.

       In this example, the restrictive clause "who has three children" is necessary to clarify which of the writer's sisters he or she will be visitng.

               ~My daughter recently attended a performance of a                                      Shakespearean play that was being performed at the                             rebuilt Globe Theater in London.

       In this case, the relative clause "that was being performed at the rebuilt Globe Theater in London" is restrictive because it is being used to specify which Shakespearean play she attended. There are many Shakespearean plays, and they are being performed all the time in many places. The relative clause narrows the field of candidates down to one.


1. If the clause is restrictive, choose "that" over "which," and don't set    the clause off with commas. *

2. If the clause is nonrestrictive, choose "which" over "that" and do               set the clause off with commas.**

*About a 99% rule.
**The relative pronoun "who" can govern both restrictive and nonrestrictive relative clauses.

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