Depending on the context, an em-dash—so named because its width matches a typesetter’s capital M—can take the place of a comma, parenthesis, or a colon in a sentence. Because it signals an abrupt break in the text, the em-dash is used best when you want to emphasize the material that follows it. (Enclosing a phrase in parenthesis will de-emphasize it; blocking it off with commas will treat it neutrally.)
In many software programs, an em-dash is created by typing two hyphens in a row—with no space before, between, or after the two—and hitting “enter.”
This versatile em-dash can be used in pairs, as seen in the following example from Richard Wydick’s Plain English for Lawyers (5th ed.):
The judge—bristling with indignation—slammed his gavel on the bench.
The em-dashes above set out text that is not necessary for comprehension of the sentence. The words, “[t]he judge slammed his gavel on the bench,” convey all the information you need to understand what happened. “Bristling with indignation” is a descriptive phrase that—as marked off by em-dashes—adds drama and flair. Setting the phrase out with commas just doesn’t have the same effect:
The judge, bristling with indignation, slammed his gavel on the bench.
You can also employ two em-dashes to enclose a piece of text that must be placed in the middle of the sentence because of the word it modifies. Here is Wydick’s example of that sort of usage:
The magistrate may rule on any procedural motion—including a motion to suppress evidence and a motion to allow or disallow discovery—at any time following the acceptance of a plea.
An em-dash can be used alone, as in this example from the online The Punctuation Guide:
After months of deliberation, the jurors reached a unanimous verdict—guilty.
The em-dash emphasizes the conclusion of the sentence, but with less formality than a colon. Consider the difference between the sentence above and the one below:
After months of deliberation, the jurors reached a unanimous verdict: guilty.
An em-dash can also take the place of a semicolon or a period between two sentences, as in this example from Plain English:
We need not reach the constitutional issue—that can await another day and another set of facts.
Replacing the em-dash above with a semicolon or period will lessen the dramatic effect of the second half of the sentence and make the resulting text feel more formal.
We need not reach the constitutional issue; that can await another day and another set of facts.
We need not reach the constitutional issue. That can await another day and another set of facts.
Strunk and White’s The Elements of Style—the seminal guide to effective writing—instructs us to use an em-dash to set off an abrupt break or interruption and to announce a summary or a long appositive (a noun phrase that renames or relates to a preceding noun). Here are two examples from the third edition:
His first thought on getting out of bed—if he had any thought at all—was to get back in again.
The rear axle began to make a noise—a grinding, chattering, teeth-gritting rasp.
While the em-dash was once considered inappropriate for more formal writing, its use in legal briefs and other legal writing has become widely accepted. Some advocates of the Plain English approach openly embrace it for its ability to liven up a piece of text. Bryan Garner, for example, says in The Winning Brief (3d ed.) that em-dashes are “genuinely useful—even indispensable—to the writer who cares about rhythm.” Here is one of Garner’s “before and after” examples showing how a piece of legal writing can be improved by replacing commas with em-dashes:
The evidence of all these efforts to protect confidentiality, combined with the fact that for all the firm’s years of experience there had never been an instance of misappropriation, amply shows that the firm made reasonable efforts to protect its trade secrets.
The evidence of all these efforts to protect confidentiality—combined with the fact that the firm had never had a trade secret misappropriated—amply shows that the firm tried to protect its trade secrets.
The “but this” version does a much better job of highlighting a “good” fact for the firm—that is, that “there had never been an instance of misappropriation.”
Be careful, however, not to wear out this handy punctuation mark. You don’t want to break the flow of your sentences too often or sound like your thoughts are constantly interrupting each other. As Garner says in The Winning Brief, “[I]f you learn how to use dashes well, without overdoing them, you’ll wonder how you ever did without them.”
About the author:
Savannah Blackwell is a former news reporter who covered government and politics in San Francisco for more than a decade and is now Of Counsel at Renne Public Law Group. She can be reached at firstname.lastname@example.org. Follow her on Twitter at @SavannahBinSF.