Commas are the most used (and abused) punctuation mark. Instead of falling into the trap of thinking you should insert a comma at each natural pause in a sentence, use this as a quick reference guide.
- Use a comma before a coordinating conjunction (and, but, for, or, nor, yet, so) that joins two independent clauses in a compound sentence. (An exception can be made if the clauses are very short.) Just be sure the conjunction is joining two clauses. Do not place a comma between the elements of a compound verb.
Examples:
Sunlight glittered on the lake, and birds chirped in the trees.
BUT
Sunlight glittered on the lake and forced me to wear sunglasses.
- Use a comma between coordinate adjectives (two or more adjectives each separately modifying the same noun). You can tell adjectives are coordinate if they can be joined by “and” and placed in a different order. Do not place a comma between cumulative adjectives (adjectives that have to be placed in a certain order to make sense) or adjectives when one of them functions with the noun as a single unit.
Examples:
A meticulous, thorough editor is essential to producing professional content.
BUT
She wore the long red dress.
A professional line editor is careful to preserve the author’s voice.
- Use a comma to separate three or more words or phrases in a series. If you are using The Chicago Manual of Style, place a comma before the last item in the series. If you are following The AP Stylebook, skip it, unless the meaning would be ambiguous without it.
Examples:
Tom, Bill, and Suzy greeted me warmly. (Chicago style)
Tom, Bill and Suzy greeted me warmly. (AP style)
- Use a comma to separate quotations from dialogue tags. However, if the quotation needs a question mark or exclamation point, do not use a comma. Also, skip the comma if the quotation is a partial quote that flows with the sentence.
Examples:
She said, “Don’t touch that stove!”
BUT
“Don’t touch that stove!” she said.
She said that the stove “was hot.”
- Use a comma to set off geographical locations and dates (when the month, day, and year are used).
Example:
She was born January 15, 1972, in New Berlin, Wisconsin, on a cold, snowy day.
- Use a comma to set off a word or phrase that introduces a sentence, particularly an interjection, an introductory participial phrase, a transitional word, or a dependent clause that precedes the main clause.
Examples (in the order they are listed):
Oh, I hope I am not late.
Running as fast as she could, she burst into the room.
Indeed, she was late.
Because my alarm clock did not go off, I was late to class.
BUT
I was late to class because my alarm clock did not go off.
- Use a comma to set off a word or phrase that is nonrestrictive; that is, it can be left out of the sentence without changing the meaning, particularly a parenthetical element or an appositive (that renames a noun).
Examples:
The dog, who hates cats, spent his day barking up a tree. (Extra information)
She spoke to her mom, Clarice, on the phone. (She only has one mom. The name is a nonrestrictive appositive.)
BUT
The dog who lives in that yard spent his day barking up a tree. (Restrictive)
She spoke to her sister Julie on the phone. (She has more than one sister, so the name is restrictive and essential to clarifying which sister she called.)
- Use a comma to separate two words that might be unclear if they were read together.
Example:
What the problem is, is not clear.
- Use a comma to set off a direct address.
Example:
I will be home late, Dad.
Many questions about commas can be cleared up by deciding whether the word or phrase is restrictive or nonrestrictive. When in doubt, consult a style guide (or your friendly neighborhood copy editor). The Chicago Manual of Style and The AP Stylebook have helpful sections on punctuation and address a few rarer issues I did not discuss here. As always, the goal is ease of reading, so keep the reader in mind.