Comma Rule No. 3—Nonessential Elements
Use a Comma to Set Off Introductory and Trailing Phrases
Oct 25, 2009
A clause is a group of words with a subject and a verb. A phrase lacks one or the other. Either a clause or a phrase can be used to start a sentence:
- While John was studying for his English exam, he felt the urge to go for a walk.
- While studying for his English exam, John felt the urge to go for a walk.
Some students question the need for the comma, yet its function becomes clear when it is removed from the following sentence:
- Although John liked Mary Nelson liked her better.
Without the aid of a comma, the reader stumbles over the sentence before realizing that “Mary Nelson” is not one person.
Trailing Clauses and Phrases
Trailing clauses and phrases serve the same function as introductory elements—providing additional information—but they come at the end of the sentence:
- Robert Mitchum starred in The Night of the Hunter, a film directed by Charles Laughton.
- It rained, causing the party to be cancelled.
Introductory elements can, of course, be moved to the end of a sentence . As a general rule, include a comma if it clarifies the meaning of the sentence or expresses a break in thought. Note that commas are needed in the following sentences
- Susan wanted to go out and play, naturally.
- He said the plot was too unrealistic, for example.
- John felt the urge to go for a walk while studying for his English exam.
- It will be over soon.
In general, writers should avoid creating sentences where commas are needed to offset both introductory and trailing thoughts:
- While waiting for the storm to pass, Martin told the children ghost stories, frightening Annie and Josh.
In this case, the main part of the sentence (Martin told the children ghost stories) becomes obscured by the two additional elements. Also, the reader naturally expects the sentence to end after “stories.”
Writers can avoid such confusion in a number of ways, such as by using a dash
- While waiting for the storm to pass, Martin told the children ghost stories—frightening Annie and Josh.
or by splitting the sentence in two:
- While waiting for the storm to pass, Martin told the children ghost stories. His eerie tales frightened Annie and Josh.
For more information on commas, see Comma Rule No. 1, Comma Rule No. 2, and Comma Rule No. 3.
Test Yourself
Correct the following sentence? (Answer appears at the end of the article.)
- Fortunately Martha booked the recital hall allowing us to hold the party the next day.
Use a comma to separate introductory or trailing elements that are not necessary to the meaning of the sentence. Read the sentence aloud to determine where a break (if any) should occur. (One possible answer: “Fortunately, Martha booked the recital hall. Her resourcefulness allowed us to hold the party the next day.”)
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