Use a comma:
- To separate words in a list or series:
The baby likes grapes, bananas, and cantaloupe.
- To separate two or more adjectives that come before a noun when and can be substituted without changing the meaning:
He had a kind, generous nature.
The dog had thick, soft, shiny fur.
Do not use the comma if the adjectives together express a single idea or the noun is a compound made up of an adjective and a noun:
The kitchen had bright yellow curtains.
A majestic bald eagle soared overhead.
- To set off words or phrases in apposition to a noun:
George Eliot, the great 19th-century novelist, was born in 1819.
Do not use commas when the appositive word or phrase is essential to the meaning of the sentence:
The novelist George Eliot was born in 1819.
- To set off nonessential phrases and clauses:
My French professor, who has an odd sense of humor, has been teaching for some 30 years.
Do not use commas when the phrase or clause is essential to the meaning of the sentence:
The professor who teaches my French class has an odd sense of humor.
- To separate the independent clauses joined by a coordinating conjunction in a compound sentence:
He lives in New York, and she lives in London.
Some people like golf, but others prefer tennis.
- To set off interrupters such as of course, however, I think, and by the way from the rest of the sentence:
She knew, of course, that he was lying.
By the way, I'll be away next week.
- To set off an introductory word, phrase, or clause at the beginning of a sentence:
Yes, I'd like to go with you.
After some years, we met again.
Being tall, she often gets teased.
- To set off a word in direct address:
Thanks, guys, for all your help.
How was your trip, Kathy?
- To set off a tag question:
You won't do that again, will you?
- To introduce a short quotation:
The queen said, “Let them eat cake!”
- To close the salutation in a personal letter and the complimentary close in a business or personal letter:
Dear Mary, … Sincerely, Fred
- To set off titles and degrees:
Sarah Little, Ph.D.Robert Johnson, Jr.
- To separate sentence elements that might be read incorrectly without the comma:
As they entered, in the shadows you could see a figure lurking.
- To set off the month and day from the year in full dates:
The conference will be held on August 6, 2001.
Do not use a comma when only the month and year appear:
The conference will be held in August 2001.
- To set off the city and state in an address:
10 Joy Street
Boston, MA 02116
If the address is inserted into text, add a second comma after the state:
Cincinnati, Ohio, is their home.
See also: The Comma