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/>.