If you don’t know the difference between the lines in parentheses above, don’t worry — you’re in the majority.
Take a look at the line I just used. It’s called an em-dash, and it’s used to emphasize an abrupt change in thought, a pause, or an interruption. Here are a couple of examples:
“I’m getting twice the gas mileage with my new car that I got with my old car.”
Okay, you’ve made a point about your car. Now, suppose you think of something else that’s notable about the car, but completely unrelated to gas mileage:
“I’m getting twice the gas mileage with my new car — the one it took the dealer three months to find with the options I wanted — that I got with my old car.”
The em-dashes let the reader know that there’s been a change in thought — or, because we’re talking car, a detour.
An em-dash can also be used as a dramatic pause to set up an expectation or emphasize what comes next.
“We have finally identified the killer as John Smith.”
Okay, now you know that John Smith is the bad guy. What a relief. But wait — (em-dash) there’s something else!
“We have finally identified the killer as John Smith — the same John Smith you’ve been married to for 27 years!”
Ouch. As if it’s not bad enough there’s been a killer on the loose, that em-dash sets off a piece of information that makes the situation even worse.
Em-dash, emphasis. That’s not actually how an em-dash got it’s name — it’s called an “em” dash because it’s the approximate width of the letter “M” on a keyboard — but it’s not a bad way to remember what it’s for.
The next one’s one’s trickier. It’s called an en-dash. It’s wider than a hyphen but not as wide as an em-dash, and it’s used to show numerical ranges in place of the word “to,” as in:
“I wrote chapters 12–17 last night.”
“You’ll have to work 8–10 hours on Saturday to make up for the time you missed.”
The en-dash is also used in place of the word “to” when connecting two things, one of which is made up of two words:
“The New York–Boston flight was canceled.”
On the other hand, if both of those things were made up of only one word, you’d use a hyphen to connect them:
“The London-Boston flight was canceled.”
It’s common for people to use a hyphen in place of an en-dash — common, but wrong. (There’s that em-dash again.)
Hyphens are easy.
A hyphen is used:
- to combine two words into one compound word, such as “well-being”
- to connect two words that modify a third word, such as in “advanced-level course”
- to separate numbers that are not inclusive (in other words, don’t need the word “to” to connect them), such as phone numbers and Social Security numbers
- when spelling out a word, such as “h-y-p-h-e-n.”
Finally, there’s the double-dash, incorrectly called a “double-dash” because it’s actually made up of two hyphens, not dashes. This has traditionally been used in circumstances where the symbol for a dash is not available, such as on a typewriter keyboard or in ASCII-only character encoding. It’s pretty much fallen by the wayside as technology has made it easy to insert an em-dash into text.
Well, gotta dash. More next time when we tackle the “I/me” substitution and — my favorite — the confusion over “preventive” and “preventative.”
And, yes, I could have used commas instead of those last two em-dashes. But that’s another story.