Two specific situations call for the use of a comma before "and." The first is created when we have three or more items in a series. This mark of punctuation is called the serial comma. For a full explanation of why we use the serial comma, please read our previous tip on the subject. (See "Serial Comma" on p. 49 in The First Fifty Tips by Nancy l. Tuten and Gayle Swanson)
The second situation occurs when "and" is being used to coordinate two independent clauses. An independent clause--also known as a main clause--is a group of words that has a subject and a verb and can stand alone as a sentence. In the following example, the independent clauses are in brackets.
Test yourself....
Call me old-fashioned, but I still appreciate a well-written sentence with a clear message.
TEST YOURSELF:
Can you tell which of the following sentences need a comma before a coordinating
conjunction?
1. The ice storm last week caused many tree limbs to fall on power lines and many people were without electricity for days.
2. The ice storm last week caused many tree limbs to fall on power lines and left many people without electricity for days.
3. Many companies are hiring chief information officers to oversee their information technology systems for only a specialist can keep pace with the rapid changes in technology.
4. Shaniqua may stay on campus for the weekend or she may decide to go home to see her high school friends.
5. Shaniqua may stay on campus for the weekend or may go home to see her high school friends.
6. We knew the roads were becoming treacherous yet we dreaded having to announce that schools would be closed the next day.
7. We knew the roads were becoming treacherous yet dreaded having to announce that schools would be closed the next day.
8. Look around for any evidence that might reveal the identity of the intruder and carefully place that evidence in a plastic bag so it can be examined closely at headquarters.
ANSWERS:
1. [The ice storm last week caused many tree limbs to fall on power lines], and [many people were without electricity for days].
2. no comma
3. [Many companies are hiring chief information officers to oversee their information technology systems], for [only a specialist can keep pace with the rapid changes in technology].
4. [Shaniqua may stay on campus for the weekend], or [she may decide to go home to see her high school friends].
5. no comma
6. [We knew the roads were becoming treacherous], yet [we dreaded having to announce that schools would be closed the next day].
7. no comma
8. [Look around for any evidence that might reveal the identity of the intruder], and [carefully place that evidence in a plastic bag so it can be examined closely at headquarters]. [Note: both independent clauses have the understood subject "you."]
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