Guidelines for Using Commas Effectively

In his essay "In Praise of the Humble Comma," author Pico Iyer compares the comma to "a flashing yellow light that asks us only to slow down." But when do we need to flash that light, and when is it better to let the sentence ride on without interruption?

Here we'll consider four main guidelines for using commas effectively. But keep in mind that these are only guidelines, not ironclad laws.

01
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Use a Comma Before a Conjunction That Joins Main Clauses

As a general rule, use a comma before a common conjunction (and, but, yet, or, nor, for, so) that links two main clauses:

  • "The drought had lasted now for ten million years, and the reign of the terrible lizards had long since ended."
    (Arthur C. Clarke, 2001: A Space Odyssey, 1968)
  • "It is hard to fail, but it is worse never to have tried to succeed."
    (Theodore Roosevelt, "The Strenuous Life," 1899)
  • "The color of the sky darkened to gray, and the plane began to rock. Francis had been in heavy weather before, but he had never been shaken up so much."
    (John Cheever, "The Country Husband," 1955)

There are exceptions of course. If the two main clauses are short, the comma may not be needed.

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.
02
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Use a Comma to Separate Items in a Series

Use a comma between words, phrases, or clauses that appear in a series of three or more:

  • "You get injected, inspected, detected, infected, neglected, and selected."
    (Arlo Guthrie, "Alice's Restaurant Massacree," 1967)
  • "Walking at night, sleeping by day, and eating raw potatoes, he made it to the Swiss border."
    (Victor Hicken, The American Fighting Man, 1968)
  • "It is by the goodness of God that in our country we have three unspeakably precious things: freedom of speech, freedom of conscience, and the prudence never to practice either of them."
    (Mark Twain, Following the Equator, 1897)

Notice that in each example a comma appears before (but not after) the conjunction and. This particular comma is called the serial comma (also known as the Oxford comma), and not all style guides require it. For more information, see What Is the Oxford (or Serial) Comma?

In the following paragraph from Animal Farm, observe how George Orwell uses commas to separate main clauses that appear in a series of three or more:

Man is the only creature that consumes without producing. He does not give milk, he does not lay eggs, he is too weak to pull the plow, he cannot run fast enough to catch rabbits. Yet he is lord of all the animals. He sets them to work, he gives back to them the bare minimum that will prevent them from starving, and the rest he keeps for himself. 
03
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Use a Comma After an Introductory Word Group

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

  • "At the front of the room, a man in a tuxedo and a light-up bow tie played requests on his portable keyboard."
    (Brad Barkley, "The Atomic Age," 2004)
  • "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, 1989)
  • Whenever I get the urge to exercise, I lie down until the urge passes.

However, if there's no danger of confusing readers, you may omit the comma after a short introductory phrase:

"At first I thought the challenge was staying awake, so I guzzled venti cappuccinos and 20-ounce Mountain Dews."
(Rich Lowry, "The One and Only." National Review, August 28, 2003)
04
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Use a Pair of Commas to Set Off Interruptions

Use a pair of commas to set off words, phrases, or clauses that interrupt a sentence:

  • "Words are, of course, the most powerful drug used by mankind."
    (Rudyard Kipling)
  • "My brother, who was normally quite an intelligent human being, once invested in a booklet that promised to teach him how to throw his voice."
    (Bill Bryson, The Life and Times of the Thunderbolt Kid. Broadway Books, 2006)

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)

Also see the discussion of restrictive elements and nonrestrictive elements at Building Sentences with Adjective Clauses.

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Nordquist, Richard. "Guidelines for Using Commas Effectively." ThoughtCo, Mar. 28, 2017, thoughtco.com/guidelines-for-using-commas-effectively-1691756. Nordquist, Richard. (2017, March 28). Guidelines for Using Commas Effectively. Retrieved from https://www.thoughtco.com/guidelines-for-using-commas-effectively-1691756 Nordquist, Richard. "Guidelines for Using Commas Effectively." ThoughtCo. https://www.thoughtco.com/guidelines-for-using-commas-effectively-1691756 (accessed November 19, 2017).