As a keen-eyed reader, you have no doubt noticed that those little horizontal lines between words and numbers come in varying lengths. As a keen-eyed typist, you'll also have noticed that your keyboard is equipped with only one key: the hyphen/minus key. And you may have observed that sometimes when you type in two hyphens to set off an interjection -- because you just know that a simple hyphen isn't up to the task—they sometimes automatically morph into a longer dash. Or not, as demonstrated in the previous sentence.  

What’s a conscientious writer to do? Stay calm and read on. The usage rules for the most commonly used dashes are relatively simple, as are the key combinations needed to produce them.  

Em-dash: When to Use

The em-dash —so named because it’s about the length of an uppercase M—is, because it’s so common, sometimes simply referred to as the dash. It’s a versatile piece of punctuation used to set off abrupt breaks in thought or as an alternative to parentheses, commas, colons, or ellipses. (Note, however, the subtle variations in effect.)

• to set off an interjection or abrupt break in thought

After two hours of inching their way through ever-heavier snowfall—why, oh why, hadn’t they listened to the weather forecast?—Kelly and Samir realized that they were in serious trouble.

• as an alternative to parentheses or commas (to set off amplifying or explanatory elements)

The troupe (who had arrived at the theatre only minutes before curtain time) delivered a stunning if somewhat breathless performance.

The troupe, who had arrived at the theatre only minutes before curtain time, delivered a stunning if somewhat breathless performance.

The troupe—who had arrived at the theatre only minutes before curtain time—delivered a stunning if somewhat breathless performance.

• as an alternative to a colon

After scouring the mall’s shoe stores for two hours, Eliza finally found what she was looking for: red patent-leather pumps in size 5. 

After scouring the mall’s shoe stores for two hours, Eliza finally found what she was looking for—red patent-leather pumps in size 5. 

• as an alternative to ellipses (to indicate a thought that trails off or is unspoken)

“Well,” said Jenny, “I suppose we could drive up on Saturday, but with Mother in hospital …”

“Well,” said Jenny, “I suppose we could drive up on Saturday, but with Mother in hospital—”

The em-dash also precedes the author’s name after a quotation. Here’s an example:

Scribbler, n. A professional writer whose views are antagonistic to one’s own.

—Ambrose Bierce (in The Devil’s Dictionary)

Em-dash or En-dash?

Traditionally, the em-dash is set without spaces on either side, as in the examples above.

However, some publishers prefer to replace the em-dash with an en-dash preceded and followed by spaces, like this:

After reading the publisher’s instructions – something he should have done beforesubmitting his manuscript – Ferdinand realized that the hyphens in his bibliography should have been en-dashes. Oh well, he thought, I suppose the copy editor will fix that.

En-dash: When to Use

You’d be amazed at how much time we editors spend on the mundane task of changing hyphens to en-dashes, particularly in endnotes and bibliographies. (Oh, those Ferdinands!) The en-dash —so named because it is about the length of an uppercase N—is used to denoteto, primarily in number and date ranges but also between words. Here are a few examples:

• July–August 1997
• 4:00–6:00 p.m.
• pages 157–159 (or 157–59, or 157–9, depending on the publisher’s preferred style)
• a 15–12 vote
• the Toronto–Winnipeg flight
• mother–daughter relationship

The en-dash is also used in compound adjectives if one element is an open compound or if both elements are hyphenated:

• post–Second World War era (or post–World War II era)
• early-childhood–late-teen years

Keyboard Shortcuts for the Em-dash and En-dash

Once you get the hang of it, typing these dashes is quite simple.

• The em-dash: On a PC, hold CTRL and ALT and press the minus sign on the keypad to the right of the keyboard. On a Mac, hold SHIFT and OPTION and press the regular hyphen/minus key.

Alternately, if you type two hyphens—without a space before or after—your word processing program should change the hyphen to an em-dash once you’ve hit the space bar after the word following the dash. 

• The en-dash: On a PC, hold CTRL and press the minus sign on the keypad to the right of the keyboard (far lower left, far upper right). On a Mac, hold OPTION and press the regular hyphen/minus key.

Alternately, if you type a hyphen—with a space before and after—your word processing program should change the hyphen to an en-dash once you’ve hit the space bar after the word following the dash. If you’re using the en-dash with spaces as a substitute for the em-dash (see above), then you’ll need to close up the spaces.     

One final point: Remember to keep your dashes consistent in your text!

If it’s information about hyphens you need, see my earlier blog.