Eight Areas of Comma Etiquette
If listing more than two things, a comma is needed between each object or idea.
- I went to the store to buy milk and bread.
- I bought milk, bread, cookies, a candy bar, and a carton of chocolate ice cream.
2. Coordinating Conjunctions: for, and, nor, but, or, yet, so (Remember them by their first letters: fanboys)
When one of these words is used to link independent clauses (a phrase that can stand on its own as a sentence) a comma is needed before the conjunction.
- I was supposed to do my homework today, but I went to see a movie instead.
- I didn't do the homework, so I had to sit in the corner at school.
3. Introductory Word Groups
When a sentence begins with a dependent clause (a phrase that depends on an independent clause to make sense), such as a prepositional phrase (using words such as "before," "after," "from," and "because of"), then a comma is needed after the phrase. If the phrase appears at the end of the sentence, though, a comma is not needed.
- After school was over, I went home and watched television.
- I ate dinner once I had finished working on my homework assignment.
- Knowing I had to go to school again in the morning, I went to bed early.
- However, I slept in late and missed class the next morning.
4. Descriptive Phrases
If the descriptive phrase (a dependent clause which acts like an adjective or adverb) merely describes without placing limitations on the object it is describing, then a comma is needed. If the descriptive phrase restricts, limits, modifies, or clarifies the meaning of the words or ideas it is describing, and is essential to getting the meaning across to the reader, a comma is not needed.
- My professor assigned a history paper which is due tomorrow.
- The paper, which is very difficult, will make up half of the grade for the course.
- The librarian who studied history has agreed to help me research the paper.
- The library, which has thousands of books, is a great place to do my research.
- The library has an extensive collection of history books ranging from medieval history to the present.
- I like to do research, unlike my sister who hates school.
5. Quotations - He said, She said
If anybody says something that needs to be quoted at the beginning, middle, or end of a sentence, commas are needed. The comma goes inside the quotation mark if the sentence will continue past the quotation. The comma goes before the quotation mark if the quote follows the beginning of the sentence. No comma is needed if the quotation ends with a question mark or exclamation point, even if the sentence will continue after the quote.
- "I have to go to the store," he said, "to buy milk and bread."
- "Can I go with you?" she asked.
6. Adjectives: Lists
If you are using more than two adjectives, commas may be needed to separate them. If the words can be shifted in order and still make sense or be separated by the word "and", then a comma is needed between the adjectives. If the adjectives only make sense if used in a certain order, or they cannot be separated by the word "and," then no comma is needed.
- The beautiful, radiant, colorful autumn leaves covered the ground.
- The radiant, colorful, beautiful, autumn leaves covered the ground.
- Four dull green leaves still clung to the tree.
7. Direct Address
If the sentence is addressing the reader directly, then a comma may be needed to separate a question, command, or statement addressed to the reader.
- I like the works of F. Scott Fitzgerald, don't you?
- Yes, they are absolutely wonderful.
8. Numbers and Addresses
Commas are used when entire dates are given, before and after the year, and to separate streets, towns and states in addresses.
- He was born January 1, 1900, at the turn of the century.
- He lived at 1000 Cedar Street, Oldetown, Virginia 24501.
Prepared by Marcy Mezzano
To answer more specific questions or to see where I got my information, see Diana Hacker, A Writer's Reference, 5th ed. (Boston: Bedford Books of St. Martin's Press, 2003).