Em dashes, which are commonly just called dashes, have four primary functions: emphasize important or essential information, enclose additional information, connect lists with sentences, and create pauses or disruptions in dialogue.
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1. Emphasize Important or Essential Information
Em dashes can be used to emphasize important or essential information midsentence or at the end of sentences. Although colons and commas can serve the save function, em dashes create a more dramatic effect.1
The weary traveler forgot something in the airport bathroom—her plane ticket.
The truck driver—riding on fumes—hoped that the neon light in the distance was a gas station.
2. Enclose Additional Information
Pairs of em dashes can showcase additional information midsentence.2
Tourists collect all sorts of dust-collecting knickknacks—particularly porcelain seashells and shot glasses—while visiting the beachside resort town.
The United Kingdom has produced many quality television programs—for example, Downton Abbey, Doc Martin, and The Vicar of Dibley—that appeal to those of us across the pond.
3. Connect Lists with Sentences
Like colons, em dashes can introduce lists. However, em dashes are usually reserved for situations where the list has an effect on the meaning of the connected sentence.3
Tom had a lot to do before transferring to his new job in Alaska—hire movers, turn off the utilities, buy warm clothing, and learn to drive a dog sled.
The sleepy copy editor overlooked several important issues in the document—misspelled words, sentence fragments, and errant commas.
4. Create Pauses or Disruptions in Dialogue
Em dashes can indicate pauses or disruptions in dialogue.4 If you follow The Chicago Manual of Style, use ellipses rather than em dashes for dialogue disruptions caused by the speaker’s confusion (like the confusion displayed in the second example below).5
John dropped the phone and turned to Milly: “You’re not going to believe this—we just inherited a fortune from my uncle Wilbur!”
“Uncle Wil—I didn’t know you had an uncle Wilbur!” exclaimed Milly.
In addition to the four functions explained above, em dashes have several less common uses, which we’ll cover in a future blog post.
Further Reading: How to Use En Dashes
1. The Chicago Manual of Style, 17th ed. (Chicago: University of Chicago Press, 2017), 6.85.
2. Bryan A. Garner, Garner’s Modern English Usage, 4th ed. (Oxford: Oxford University Press, 2016), 750; Publication Manual of the American Psychological Association, 6th ed. (Washington, DC: American Psychological Association, 2010), 4.06; The Chicago Manual of Style, 17th ed. (Chicago: University of Chicago Press, 2017), 6.51, 6.85.
3. Bryan A. Garner, The Chicago Guide to Grammar, Usage, and Punctuation (Chicago: University of Chicago Press, 2016), 449 (p. 370).
4. Bryan A. Garner, The Chicago Guide to Grammar, Usage, and Punctuation (Chicago: University of Chicago Press, 2016), 500 (p. 370–71); The Chicago Manual of Style, 17th ed. (Chicago: University of Chicago Press, 2017), 6.87.
5. The Chicago Manual of Style, 17th ed. (Chicago: University of Chicago Press, 2017), 13.41.