In the book Eats, Shoots & Leaves: The Zero Tolerance Approach to Punctuation, plucky Lynne Truss describes punctuation as “a courtesy designed to help readers to understand a story without stumbling.”

With this in mind, I would name the em dash as the most chivalrous punctuation mark of all time.

As I often explain to punctuation newbies, em dashes (or long dashes) are used to indicate a pronounced interruption or break in thought. They should be used sparingly and only when another punctuation mark (such as a comma or colon) will not suffice. For example:

• Em dashes can be used when you want to introduce additional information in a sentence, but you don’t want to set it off with commas or parenthesis. “My piano teacher—an exceptionally patient woman—was visibly agitated by my ham-fisted playing.”

• Em dashes can also be used to separate a pronoun from what it refers to. “Mr. Harris is the perfect gentleman—articulate, charming, and handsome.”

• Em dashes can also be used to convey a more emphatic aside. “Your brother—no matter what he says—cannot make you unconscious just by looking at you.”

The best use of an em dash I have ever seen was in an issue of my alumni association newsletter. The article was introducing the newest longhorn selected to serve as Bevo, the University of Texas mascot. A brief family history of the animal included this sentence: “Bevo’s father was killed when he was struck by lighting—his hooves and horns were blown right off—leaving Bevo an orphan.”

Em dashes work perfectly in this sentence because the clause “his hooves and horns were blown right off” would simply not work if it were set off with commas or put in parentheses.

Please do not use two hyphens to make an em dash (or your hooves and horns may be blown right off). Create an em dash on a Mac with option/shift/hyphen. On a PC, it’s Ctrl/Alt/minus sign. In html, it's — .

I hope this post can convince even the most stubborn skeptics of the utility of this unassuming punctuation mark. For emphasis, think em dash.

A version of this story first appeared on the author’s blog Impertinent Remarks.

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