The Confusing, Confounding, Often-cursed Comma
by Mariella Morgan
There are many rules for using commas -- 23 in one list I saw -- but the one thing they have in common is that all commas separate words, phrases, two dependent clauses, one dependent clause and one independent clause, or two independent clauses.
WHAT YOU NEED TO REMEMBER: COMMAS SEPARATE, THEY DON'T JOIN. If you can remember those five words, you will avoid making the mistake freshmen make most often, the comma splice. I'll talk about that mistake later.
Bryan A. Garner gives nine rules for common use in his book Garner's Modern American Usage, pp. 654-655.
1. "The comma separates items in a list of more than two."
EX: Ham and eggs, steak and eggs, and steak and lobster have been added to the menu.
This examples shows that the Oxford comma, the comma before and, is necessary for clarity many times in sentences and should not be omitted. If you are British, you probably don't use the Oxford comma unless it is necessary for clarity.
2. "The comma separates coordinated main clauses (compound sentence)."
EX: Cars park on the left, and buses park on the right.
Garner notes 2 exceptions -- I know that exceptions are frustrating, but here they are anyway.
1. "When the main clauses are closely related-"
EX: Follow my rules [no comma] and you'll do well here.
2. "When the subject of the second independent clause, being the same as in the first, is not repeated" (also called compound
EX: He ran to the door [no comma] and threw it open.
3. "The comma separates most introductory matter from the main clause, often to prevent misunderstanding."
EX: However, I disagree with your agreement. (word)
In the meantime, she waited patiently for her hero to rescue her. (phrases of three or more words or necessary for clarity)
That said, I forgive you for hurting me. (subordinate clauses, even ones with only two words)
Garner gives 1 exception: when the introductory matter is a very short phrase.
EX: On Friday [no comma] I will see my doctor for the test results.
4. "The comma marks the beginning and end of a parenthetical word or phrase, an appositive, or a nonrestrictive clause.
EX: I am sure, therefore, that you will have enough votes to win the election.
Mary Alice Johnson, my sister-in-law, is a new state representative.
Fred, who is new here, complained about the food.
Note: A nonrestrictive clause is a dependent clause that gives the reader information that the main clause doesn't depend on for its meaning. You can leave it out, and you will still have a good sentence.
5. "The comma separates adjectives that each qualify a noun in the SAME WAY. If you could use and between the adjectives, you'll need the comma.
EX: He was a quiet, reserved person.
If the adjectives qualify the noun in DIFFERENT WAYS, don't use a comma between them.
EX: She worn a bright red blouse.
6. "The comma separates a direction quotation from its attribution."
EX: "Honey, I'm home," Desi said.
"A comma is not used to separate quoted speech that is woven into the sentence."
EX: People remember TV catchphrases such as "Honey, I'm home."
7. "The comma separates a participial phrase."
EX: Having had lunch just a few hours before, I wasn't interested in going out for a burger.
8. The comma is used in informal letters at the end of the salutation and the complimentary close.
EX: Dear Abby, Yours truly,
9. "The comma separates parts of an address or a date."
EX: 269 E. Austin Rd., Newport, Iowa October 11, 2010
the Queen of English