The University of Scranton Writing Center

This writing tutorial provides eleven basic rules which
explain whether comma usage is necessary in
particular instances.

An example follows each rule.

These rules are only basic guidelines and do not
include every possible grammar situation which
requires a comma.

These rules were found on the Purdue University
Online Writing Lab Website; a proper MLA citation
can be found at the conclusion of this tutorial.

Use commas to separate independent clauses
when they are joined by any of these seven
coordinating conjunctions: and, but, for, or,
nor, so, yet.

Example: Joe wanted to go to class, but he
forgot to set his alarm.

Use commas after introductory:
 clauses,
 phrases,
 words that come before the main clause.

Example: When Joe woke up, he realized he
had missed his first class.

Use a pair of commas in the middle of a
sentence to set off clauses, phrases, and
words that are not essential to the meaning
of the sentence. Use one comma before to
indicate the beginning of the pause and one
at the end to indicate the end of the pause.

Example: Joe’s professor, Mrs. Jane Doe,
assigned two papers this week.

Do not use commas to set off essential
elements of the sentence, such as clauses
beginning with that (relative clauses). That
clauses after nouns are always essential. That
clauses following a verb expressing mental
action are always essential.

Example: Joe used the computer that his
parents had given him.

Use commas to separate three or more
words, phrases, or clauses written in a series.

Example: Joe’s three favorite colors are red,
white, and blue.

Use commas to separate two or more
coordinate adjectives that describe the same
noun. Be sure never to add an extra comma
between the final adjective and the noun
itself or to use commas with non-coordinate
adjectives.

Example: Joe only eats green, leafy
vegetables.

Use a comma near the end of a sentence to
separate contrasted coordinate elements or
to indicate a distinct pause or shift.

Example: Joe told his parents that his
favorite class was Spanish, not French.

Use commas to set off phrases at the end of
the sentence that refer back to the beginning
or middle of the sentence. Such phrases are
free modifiers that can be placed anywhere in
the sentence without causing confusion.

Example: Joe’s history project was complete,
a ten-page report on colonialism.

Use commas to set off all geographical
names, items in dates (except the month and
day), addresses (except the street number
and name), and titles in names.

Example: On December 4, 2008, Joe visited
the University of Scranton Writing Center in
Scranton, Pennsylvania.

Use a comma to shift between the main
discourse and a quotation.

Example: Joe told his friends, “The Writing
Center is located on the fifth floor in St.
Thomas Hall.”

Use commas wherever necessary to prevent
possible confusion or misreading.

Example: Before getting up to leave, his
friend promised to visit the Writing Center.

Example: Did you see my friend, Joe?
"Commas - The OWL at Purdue." Welcome to the Purdue
University Online Writing Lab (OWL). N.p., n.d. Web.
12 July 2009.
<http://owl.english.purdue.edu/owl/resource/607/01/>.