Rules of Comma UsageThere are specific rules for using the comma, but keep in mind the following:• The comma is never inserted into a sentence where you believe you would “take a breath;” after all, do you really read everything you write aloud?• The comma is never inserted into a sentence where you can use a period; if you do, you create a comma splice.
8 Most Common Rules1. To separate main clauses linked by a coordinating conjunction2. To set off introductory elements3. To set off non-essential or parenthetical elements4. To separate elements in a seriesn To separate coordinate adjectivesn To set off quoted elementsn To avoid confusionn Typographical reasons
RULE #1: To separate main clauses linked by a coordinating conjunction (and, but, for, nor, yet, or, so, although)I enjoy sending email, so I seldom write by hand anymore.I enjoy sending email, yet I rarely have the time to write it.I enjoy sending email, but prefer surfing the internet.Note that what comes before the comma is a complete sentence and what comes after the comma and coordinating conjunction is also a complete sentence.An excellent approach to learning this rule is to memorize the 8 coordinating conjunctions listed above.
RULE #1: To separate main clauses linked by a coordinating conjunctionIf the coordinating conjunction is not linking main clauses, then a comma is not necessary.Email is fast but impersonal.Never follow the coordinating conjunction with a comma, even if you would pause there when speaking.
RULE #2: To set off introductory elementsNatural word order in English prefers the subject of the sentence to be stated first, followed immediately by the main verb; if we move an element that typically follows the main verb to beginning of the sentence, then a comma should come immediately after that element.When first created, the internet was used only by the military.Over the years, more and more people are using the internet.
When not to use a comma after an introductory elementThere are also introductory words and phrases (however, therefore, in conclusion, etc.) that require a comma to follow.However, the NSF has made the internet widely available.If the introductory element is extremely brief (i.e. a single, one-syllable word), then the comma, although correct, may be omitted.Now most Americans have internet access.
RULE #3: To set off non-essential or parenthetical elementsThe internet, which was invented by the military, is a powerful research tool.Her new computer, an IBM laptop, is much faster than her old one.The internet service is, of course, an added expense.Note that 2 commas are always used, never just one.If the element is essential to an understanding of the sentence, then no commas are used.The web designer who works for our competitor uses professional software.
Understanding the difference between essential and non-essential phrasesIn order to determine whether a phrase is essential or not to the sentence, you must consider context.My brother, who is a teacher, lives in Lexington.My brother who is a teacher lives in Lexington.Why the difference? In the first sentence, I only have one brother, so the fact he teaches is extra (or non- essential) information; in the second sentence, I must have more than one brother, so the fact he teaches (and does not drive a bus) is essential to understand the sentence.
RULE #4: To separate elements (more than 2) in a seriesThe internet is fast, efficient, and addictive.The internet is fast, efficient, but addictive.If you were taught the alternative rule of omitting the comma before “and,” that is fine. Just be consistent in your writing.The internet is fast, efficient and addictive.
RULE #5: To separate coordinate adjectivesThe designer created an effective, dynamic webpage.If you can rewrite the sentence with an “and” (or “but”) between the adjectives, then a comma is needed.The designer created an effective and dynamic webpage.If no “and” or “but” is possible, then a comma is unlikely to be needed.The webpage designer is a little old lady.
RULE #6: To set off quoted elementsIn his article, Johnson states, “cyberspace was becoming the new final frontier” (6).Do not use a comma if the quotation is presented as indirect speech.In his article, Johnson states that “cyberspace was becoming the new final frontier” (6).
RULE #7: To avoid confusionUnclear:Outside the acceptable use policy of the computer classroom is clearly posted.Better:Outside, the acceptable use policy of the computer classroom is clearly posted.Best (rewrite the sentence using no commas):The acceptable use policy of the computer classroom is clearly posted outside the room.
RULE #8: Typographical reasonsCommas divide elements in dates and addresses.The computer company relocated its main office from Cincinnati, Ohio, to Northern Kentucky.The office opened on January 1, 2001, for its first day of business.