Northcentral University Writing Center
Applying Comma Rules

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Writing Center

Applying Comma Rules


The comma is the most used and the most misused piece of punctuation in English. Commas generally serve to separate items from one another and to cause a pause in reading. Commas also have conventional uses that must be observed. Omitting needed commas or inserting commas which are not needed will confuse the reader and lead to misunderstanding.


Following are the basic comma rules for academic writing:


Rule One:          Use a comma before a coordinating conjunction connecting two main

 clauses. Coordinating conjunctions are: and, but, or, nor, for, yet so.


Bob arrived at school early, and he was greeted by the teacher and her staff.



Rule Two:          Use a comma to set off introductory elements, such as long

                         prepositional phrases, participial phrases, or subordinate clauses.


In front of the classroom and behind the lectern, the professor began his lecture.

If the mail arrives early, please send it to me at once.

Exhausted, the swimmer climbed out of the pool as the winner.

Ignoring the needs of the electorate, the CEO made his decision and proceeded

with the plan.


Rule Three:        Use commas to divide items in a series.


            I like dogs, cats, and birds. 


            *Note that for long items in a series, the semi-colon is used to divide the items.


            I like dogs with long hair and cold noses; cats with short claws and a friendly

            nature; and birds who do not chirp all night and keep the neighbors awake.


Rule Four:      Use commas to set off non-restrictive appositives.


The White House, the residence of the U.S. President, sits in the middle of

Washington, D.C.


*Note that a non-restrictive appositive is a phrase used to provide additional information about the noun which it modifies. If the non-restrictive appositive is left out, the principal meaning of the noun being modified would not be lost.


Rule Five:      Use commas to set off parenthetical expressions.


The artist, for example, was represented by his publicist.


*Note that a parenthetical expression is a supplementary, explanatory or transition word or phrase. These expressions include for example, however, as a result, of course, indeed, consequently.


For more information on comma usage, see Revising Comma Splices in the Revising the Draft for Conventions section of the NCU Writing Center. Additionally, writers are also encouraged to visit the Writing Centers at Colorado, Purdue, and Chapel Hill.