There are two types of dashes: the em dash and the en dash. Their names come from their respective length:
The em dash is formed with two hyphens (–) and no extra spaces, which MS Word reformats automatically to a longer dash when you keep typing.
The en dash is formed with one hyphen and no spaces around it. Again, as you keep typing, Word will lengthen the hyphen slightly to create an en dash.
Many style manuals suggest you leave no spaces around a dash (word—word). It is not unusual, though, to see instead a dash with spaces around it (word – word). Whatever usage you follow, the main thing is to be consistent.
The Em Dash
Since the em dash is the most common dash, we will just refer to it as “the dash.” The purpose of the dash is to indicate a sudden shift in a sentence or to set off and draw attention to specific words.
Either way, the dash adds some style to your writing. Dashes make you appear nonchalant, confident, even witty. So dash off a dash—you’ll look dashing!
Let’s review the principal uses.
Before a Final Explanation
A dash is a great way to extend a sentence and add a final explanation, a list, or an appositive phrase:
In the 1986 FIFA World Cup, the quarter-final was a contest between England and Argentina—two nations that had been at war over the Falkland Islands four years earlier.
He ordered an expensive-sounding bottle of champagne—a Banlieue de Paris.
She did not want to open the envelope—it could wait.
Richard Filigree spent four months tracking the Australian elephant—the most elusive animal he had ever studied.
A flywheel is a wheel that stores and transfers rotational energy—something that is especially useful when you want to turn intermittent power into a continuous supply of energy.
Fatima’s project on the Edo culture of Japan included three demonstrations—a sumo wrestling contest, a recitation of haiku, and a dramatic demonstration of seppuku.
You’ll note that before an appositive or a list you would normally use a comma or colon. A dash simply creates a more casual effect.
After an Introductory Element
You can use a dash not only before a list, but also after one:
Tsunamis, typhoons, and tornadoes—these are a few of my favourite things.
While phoning my fiancée, arranging for a tow-truck, and writing down the registration information from the truck driver, who did not want to cooperate—while doing all these things I had no time to cry over my crumpled car.
Notice how in the second example—with its rather long list—the dash allows you to gather all your thoughts before concluding the sentence.
Around Parenthetical Information
Extra information is normally placed between commas or parentheses. This kind of information is called “non-essential” or non-restrictive” because it does not restrict or change the meaning of the rest of the sentence—it is just extra material.
You can also place such information between dashes, though the effect is different. Dashes make the words stand out. Here are some examples:
Until 1993—when the London Convention banned the practice—every nuclear nation simply dumped its radioactive waste into the world’s oceans.
After a brief negotiation, the union leaders—to everyone’s surprise—called off the general strike.
Alyson Twinklestar’s piano students—Esther, Emma, and Iris—were always playing pranks.
If I had my own butler—and a mansion to put him in—I would host the most wonderful parties.
As you can see from the examples, the extra material can be one or more appositives, a phrase or clause, or any other interrupting expression.
With a Break in Speech
The dash also has a rather practical function. It suggests a sudden break or shift in a speech:
“You would not dare shoot me! You would not—”
“Do you want to marry—actually, never mind.”
Finally, you can use a dash to indicate dialogue or in a list that uses bullet form.
Here’s how dashes can be used for dialogue:
—Have you seen his latest exhibition?
—At the gallery?
—In the park.
—No, I’m not into artists exhibiting their wares in the park.
And here’s a list that uses dashes:
This government has four main priorities:
—Raise personal income taxes
—Build more coal power plants
—Give generous severance packages to any bureaucrats with ties to the previous government
—Have more children in cabinet positions
The En Dash
As mentioned, sometimes an en dash is simply used in the place of an em dash. This is quite common in British texts.
Otherwise, the en dash has a few specific uses (though a hyphen is fine too).
The shorter en dash can be used to mean “to”:
Mahatma Gandhi (1869–1948) liked to air his dirty laundry.
The Caterpillars Rugby Club won 25–17.
The Paris–Dakar rally was first organized in 1979.
It can also connect compound adjectives, but only if they include a proper noun:
I missed my New York–Tel Aviv connection.
I love your Emily Dickinson–like obsession with dashes.
She studied post–Civil War politics.
By contrast, other compound adjectives can be connected using a hyphen.