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When to Use a Comma before "And"

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 our book of writing tips or find the link to the "Serial Comma" tip in our online tip archive.)

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:

  • [Miguel took piano lessons for sixteen years], and [today he is an accomplished performer].

The use of the comma would also apply when any of the seven coordinating conjunctions (and, but, or, nor, for, so, yet) join two independent clauses.

Notice in the next example that we do not use a comma before "and" because it does not join two independent clauses but merely joins two verbs:

  • Miguel took piano lessons for sixteen years and today is an accomplished performer.

Here we have only one independent clause—two verbs ("took" and "is") but one subject ("Miguel").

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Keep in mind that length is not a factor in determining when to use the comma before a coordinating conjunction. In this next example, even though the sentence is long, we do not need a comma because we have only one independent clause. The conjunction "but" merely connects the two verbs "wanted" and "could not afford":

  • Sigfried wanted to go back to school to earn a college degree but could not afford to quit his job and lose his health care benefits.

Some writers omit the comma before a coordinating conjunction if the two independent clauses are short, as in these examples:

  • I drove home but he stayed.
  • Give me the keys and get in the car.

Although it is not necessary to use a comma before "but" or "and" in these sentences, it would not be considered wrong to do so since we do, in fact, have two independent clauses in each sentence.

Keep in mind, too, that the subject of those independent clauses that issue commands (they are called imperatives) is the understood "you," as in the clauses "Give me the keys" and "get in the car" in the second example above.

Since commas are used in pairs to enclose phrases that interrupt a clause or that are intended to function parenthetically, a writer may choose to place a comma before "and" (or any of the seven coordinating conjunctions) when the conjunction launches such a phrase:

  • Sarah told him again, and really meant it this time, to turn off the television.
  • Alice will ask John once, but only once, to forgive her.

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."]

Copyright 2004 Get It Write

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