Tip Sheet: Comma Usage


The comma exists to help readers. When properly placed, commas clarify meaning by helping readers organize information. Without it, sentence parts can collide into one another and cause confusion. Rules for commas and examples of proper usage follow below.


To get a proper perspective on the comma, let's examine its appropriate use and then look at some of its inappropriate uses.

First, its proper uses:
1. Commas separate items in a series.
The forecast calls for light showers, some clearing, and morning fog.

2. Commas separate two independent clauses connected by a coordinating conjunction (and, or, nor, but, so).

Seven men were arrested on the east side, and ten more were taken into
custody six hours later.

3. Commas set off long introductory clauses and phrases and shorter clauses and phrases that would be confusing without the comma.

When the fire alarm went off for the third time that night, the motel clerk
finally called the fire department.

4. Commas set off non-restrictive (non-essential) clauses, phrases, and modifiers from the rest of the sentence.

Example of restrictive (essential) clause:
Two sisters who sought refuge in a church died when the tornado hit.

Example of non-restrictive (non-essential) clause:
Chateau Montelena, which is one of the more expensive Northern California wineries , won a gold medal for this year's bottling of Chardonnay.

5. Commas separate descriptive modifiers of equal rank. If you can use adjectives interchangeably and can successfully insert the conjunction "and" between them, they are coordinate and require a comma.

Scientists will not predict the next activity of the fickle, explosive volcano.

6. Commas set off parenthetical expressions.
These same council members, you may recall , voted themselves a 35 percent
pay increase last year.

7. Commas are used when the absence of a pause can cause confusion.
For the mayor, going fishing is enough of a vacation.

8. Commas are used to set off participle phrases that modify some part of the
independent clause.

The Senate adjourned today, having successfully defeated a filibustering attempt.

Next, here are examples of the comma's improper uses:
1. Do not use a comma to separate two independent clauses that are not joined
by a coordinating conjunction. To do so would cause a comma splice.

The inflation rate dipped to 3 percent, the unemployment rate stayed constant.

a. Use a semicolon to link the clauses:

The inflation rate dipped to 3 percent; the unemployment rate stayed

b. Use a coordinating conjunction with a comma:

The inflation rate dipped to 3 percent, but the unemployment rate
stayed constant.

2. Do not use a comma to introduce a subordinate clause. (Tip: the use of
a comma before the conjunction "because" is one of the biggest offenders.)

The mayor decided to visit the protest site because she needed a first hand

But... if the subordinate clause is being used to introduce the sentence, a
comma is required:
Because she needed a firsthand report, the mayor decided to visit the
protest site.

3. Do not use a comma to separate a noun or pronoun from its reflexive.
Bryant himself will discipline the players.

4. Do not use a comma between a word and a phrase that amplifies it if
it will create a "false series."

Example of a Confusing Series:
Rescuers discovered seven bodies, six transients, and one firefighter.

Rescuers discovered seven bodies-- six transients and one firefighter.

5. Don't use a comma to precede a partial quotation.
The mayoral candidate charged that the incumbent was "a charlatan of
the lowest order."

If the quotation is a full sentence, it should be preceded by a comma:

The defense counsel asked, "How would you like to be sent to prison for
a crime you didn't commit?"


Decide whether or not the following sentences need commas. Provide a brief justification for each comma you insert, referring to the rules above.

1. Teratology the study of deformities derives its name from the Greek word
for monster.

2. Hearing the train whistle caused Zach to look up in anticipation and delight.

3. The blues is a distinctly American sound yet it has often received more
attention in Paris than in New York.

4. All roads may lead to Rome but my mother and I got hopelessly lost trying
to drive there from Naples.

5. The Gamble House one of the finest examples of the arts and crafts architecture in America is located in Pasadena California.

6. The most hard working of all the students in the class she despaired when others received substantially higher grades.

7. You know I can't tolerate such behavior Susan.

8. Exhausted and penniless he stared at the brightly lit interior imagining a
warm fire a table laden with delicious hot food and large beds with clean
white linens.

9. It was a charming older home whose turn-of-the-century decor enhances its