An em-dash (—) is longer than an en-dash (–) and three times as long as a hyphen (-). Don’t be afraid of it. It is useful and versatile, and too many writers avoid it.
Em-dash uses
1. Em-dashes set apart parenthetical phrases or clauses in a sentence. In this use, em-dashes are similar to commas and parentheses, but there are subtle differences. For example, em-dashes are used when a parenthetical remark contains an internal comma or would otherwise sound awkward if enclosed by commas. Here are a few examples of em-dashes used well for this purpose:
Steely Dan’s title track to FM—a justly forgotten, Robert Altman-inspired 1978 comedy that tries to pass off Foreigner, Foghat, and REO Speedwagon as paragons of rock rebellion—initially sounds like an extension of that movie’s middle-of-the-road sounds. [AV Club]
Since 2007, the consensus of the economic establishment—bankers, policymakers, CEOs, stock analysts, pundits—has been catastrophically wrong. [Slate]
Both Dagan and Diskin oppose military action against Iran unless all other options – primarily international diplomatic pressure and perhaps sabotage – have been exhausted. [Guardian]
In other cases, em-dashes are used where parentheses would interrupt the flow of a sentence—for example:
The president’s nephews — sons of his late brother — include Amar, the deputy director for national security . . . [New York Times]
2. An em-dash can indicate a sudden break, an interruption, or a trailing off—for example:
HOWARD: … She’s totally unapologetic, she’s–
CHEW-BOSE: She’s everything. [Interview Magazine]
3. Em-dashes can replace colons or serve as harder versions of commas (similar to semicolons). While parenthetical em-dashes often operate in pairs (see the examples under the first point above), hard-comma em-dashes often function alone—for example:
The all-renewable energy sector is 30 years away — and always will be. [Salon]
It’s that time of year again — time for New Year’s Resolutions! [Pegasus Books]
Em-dash typography
As you can see from the above em-dash examples, which are copied from their sources with no typographical changes, publications have varying standards for em-dash typography. Some use the equivalent of three linked hyphens surrounded by a space on each side (like — this), and some omit the surrounding spaces (like—this). Others, like the online New York Times, use an en-dash (or the equivalent of two hyphens) surrounded by spaces (like — this). Some use an en-dash with no spaces (like–this). And we’ve noticed that some writers, especially on blogs and in other informal contexts, increasingly use a single hyphen surrounded by spaces (like – this) instead of an em-dash.
