Commas

Commas divide parts of a sentence. The comma has more uses and variance of usage than any other mark of punctuation. These are the universally accepted uses of the comma:

Note: Not all style guides mention each of these uses explicitly, but all of these uses are demonstrated within the text of each guide.

Between Clauses with a Coordinating Conjunction

I’ll eat with you, but I won’t work with you.

He went to France, and he enjoyed himself, but he didn’t find what he was looking for.

Note: Most style guides consulted permit the omission of this comma if the independent clauses are short.

Note: The Chicago Manual of Style permits the stylistic omission of this comma.

Around Nonrestrictive Elements

Commas surround elements in a sentence that you can remove without altering the meaning of the sentence.

His home, which is square and brown, used to be my home.

She received a slice of pepperoni, which was not what she asked for.

Jonathan, eating his chicken, complimented the man’s shoes.

Between Items in a Series

Cars, trucks, and vans

He eats, sleeps, and writes.

There are three XHTML document types: transitional, strict, and frameset.

Note: Style guides have different preferences regarding the serial comma.

Note: If items in a list or series contain commas, they are separated by semicolons.

After an Introductory Word Group

Commas follow an introductory word group. Introductory word groups include adverbial modifiers, participial phrases, and interjections.

For our style guide, please use the serial comma.

Strictly speaking, such a comma is not necessary in most circumstances.

Yes, that appears to be true.

As a matter of fact, some people do mind.

Note: The AP Stylebook and the Merriam-Webster Guide to Punctuation permit (and The Chicago Manual of Style recommends) omitting this comma when there is no ambiguity.

See Examples

Note: The Chicago Manual of Style and the Merriam-Webster Guide to Punctuation suggest omitting this comma when the modified clause begins with the primary verb.

See Examples

Between Coordinate Modifiers

He was a beautiful, misunderstood man.

That is the most ridiculous, offensive nonsense I’ve ever had the misfortune of hearing.

She quietly, steadily made her way to the living room.

Note: One method (according to The American Heritage Dictionary) of deciding if two adjectives are coordinate is by replacing the comma with the word “and.” The method specifies that if the word “and” can comfortably separate two modifiers, a comma can also separate them.

Note: The Chicago Manual of Style and the Merriam-Webster Guide to Punctuation permit the stylistic omission of commas separating modifiers.

For Quotations

Commas set off single-sentence quotations, and they replace periods at the end of a quote that does not conclude a sentence.

They shouted, “We are everything!”

“I don’t believe it,” he said. “I can’t believe it.”

Note: Some style guides suggest the punctuation surrounding a quote depends on its use within the sentence.

Note: The AP Stylebook and The New York Times Manual of Style and Usage specify the use of a colon to set off a quotation of more than one sentence.

Note: The The American Heritage Dictionary does not provide an explicit example of a comma replacing a period at the end of a quote that does not conclude a sentence, but I am inclined to believe that the writers approve of the usage because of its prevalence elsewhere.

Around Transitions

One would never, for example, spontaneously turn invisible.

She could not, however, recall what she had said the Saturday before.

Around Parentheticals

He, despite his misgivings, gave them his blessing.

How, and indeed why, do we walk upon this green Earth?

He was ready for action, strange as that is.

Note: Some style guides suggest using dashes in this way.