The Comma in Punctuation

The little mark indicates a pause or break in a sentence

4 Rules for using commas

 ThoughtCo

comma (,) is a punctuation mark that separates elements and ideas within a sentence. The comma is the most common mark of punctuation—and the most commonly misused.

In his Time magazine essay, In Praise of the Humble Comma", author and essayist Pico Iyer compared the punctuation mark to "a flashing yellow light that asks us only to slow down." Knowing when to insert that flashing light (the comma) and when is it better to let the sentence ride on without interruption is a conundrum that challenges even the most expert of writers.

Learning a few simple rules can help you master when to use a comma and when to omit it.

How to Use Commas Correctly

Place a comma in front of a coordinating conjunction (and, but, for, nor, or, so, and yet) that joins two independent clauses in a compound sentence. Author Maya Angelou used this example of a comma before a coordinating conjunction in "I Know Why the Caged Bird Sings":

"I sliced onions, and Bailey opened two or even three cans of sardines and allowed their juice of oil and fishing boats to ooze down and around the sides."

Note how Angelou's sentence contains two independent clauses—each could stand on its own as a sentence—but the author, instead, decided to join them with the coordinating conjunction and, which was preceded with a comma. If the two independent clauses are short, however, you can usually omit the comma:

  • Jimmy rode his bike and Jill walked.

In most cases, do not use a comma before a conjunction that links two words or phrases:

  • Jack and Diane sang and danced all night.

In a Series

Use commas to separate words and phrases in a series of three or more:

"Everyone hollered, hooted, back-slapped, and jumped into the air."

- Keith Nolan, "Into Cambodia"

Use a comma to separate adjectives that are coordinate (adjectives that are interchangeable before or after a noun):

"The books are trim, crisp, clean, especially in the moment when they arrive from the printer in a cardboard box."

- John Updike, Self-Consciousness

You can tell whether adjectives are coordinate by inserting the conjunction and between them. If the sentence makes sense, the adjectives are coordinate and should be separated by commas. By contrast,  cumulative adjectives—two or more adjectives that build on one another and together modify a noun—are generally not separated by commas:

"I wrote in a marble-floored room at the back of the little lavender house we rented on Essex Road."

- John Updike, "Self-Consciousness"

After an Introductory Clause

To signal a pause, use a comma after an introductory word, phrase, or clause:

"For the first few days of his life, Wilbur was allowed to live in a box near the stove in the kitchen."

- E.B. White, "Charlotte's Web"

Use a comma after a phrase or clause that precedes the subject of the sentence:

"Lacking brothers and sisters, I was shy and clumsy in the give and take and push and pull of human interchange."
- John Updike, "Self-Consciousness"

If the introductory element doesn't require a pause, you can usually omit the comma

To Set Off Phrases

Use commas to set off interrupting phrases and nonrestrictive elements—words, phrases, or clauses that provide added (though not essential) information to a sentence.

For example:

"He sat back in his chairslightly ashamed of himselfand laid down his pen."
- George Orwell, "Nineteen Eighty-Four"

But don't use commas to set off words that directly affect the essential meaning of the sentence:

"Your manuscript is both good and original. But the part that is good is not original, and the part that is original is not good."
- Samuel Johnson

Other Uses for Commas

Use a comma between the day and year in a date, in numbers greater than 999 (except in street addresses and years), and between the city and state in a location:

  • The last time I was there was Jan. 8, 2008.
  • The house is located at 1255 Oak Street, Huntsville, Ala.
  • He had 1,244,555 marbles in his collection.
  • In the year 1492, Columbus sailed the ocean blue.

When a phrase refers to a month, day, and year, set off the year with a comma, says "The Associated Press Stylebook, 2018":

  • Feb. 14, 2020, is the target date

The Oxford, or Serial, Comma

The Oxford comma, also called the serial comma, precedes the conjunction before the final item in a list of three or more items. It is usually optional and is generally not used when only two parallel items are connected by a conjunction: faith and charity:

  • This song was composed by Moe, Larry, and Curly.

Though the AP Stylebook is a notable exception, most American style guides recommend using the serial comma for the sake of clarity and consistency. In contrast, most British style guides discourage use of the serial comma unless the items in the series would be confusing without it. As Joan I. Miller and Bruce J. Taylor say in "The Punctuation Handbook":

"Nothing is gained by omitting the final comma in a list, while clarity can be lost in some cases through misreading."

The Oxford comma is so called because it has traditionally been used by editors and printers at Oxford University Press. New Englanders may favor the term Harvard comma (the convention is also followed by Harvard University Press).

Commas and Meaning

The comma can alter the meaning of a sentence, says Noah Lukeman in "A Dash of Style: The Art and Mastery of Punctuation." Consider:

  • The windows with the glass treatment are holding up well.
  • The windows, with the glass treatment, are holding up well.

In the latter sentence, the windows are holding up well because of the glass treatment, says Lukeman. In the former, the windows, which were treated with a glass treatment, are holding up well in general.

"The entire meaning of the sentence changes, simply due to the comma placement," he notes.