2. Em-dashes Instead of Commas
If you were wondering whether you could have used commas in place of parentheses or em-dashes in the examples above, you can. In terms of adding emphasis to a phrase, the comma falls somewhere between the parentheses and the em-dash. Another thing to keep in mind is that many sentences already have commas so using them to set off a descriptive phrase can make things a little crowded with commas. Let’s revisit our “Dennis road trip” sentence to use as an example.
Dennis took his car, a tiny, two-door Honda, on a weekend road trip.
See, lots of commas. An em-dash gives you another option when you are dealing with a phrase that describes or elaborates upon a noun. But again, use it only when it is clear that you want to add emphasis to a phrase.
For instance, in the sentence below the em-dash highlights an unusual (and unfortunate) fact about this person’s friend:
Her best friend, indeed her only friend, did not even send her a birthday wish.
Her best friend—indeed her only friend—did not even send her a birthday wish.
As we saw with parentheses, when an em-dash replaces the commas that set off a phrase, it adds more emphasis. It also gives a writer the opportunity to avoid “comma clutter.”
Em-dashes in Place of a Colon
Just as em-dashes add emphasis when they take the place of commas or parentheses, so do they add emphasis to an already emphatic punctuation mark: the colon. You want to be sparing in your use of an em-dash in place of a colon, and remember that by using an em-dash instead of a colon, your style becomes less formal. If that’s your intention and you want to add special emphasis to a word or phrase, then use the em-dash. Take the following sentence as an example.
After 1,000 miles of sputtering along in his tiny Honda, Dennis could think only one thing as he approached his driveway—home.
Of course, you could use a colon in this sentence, but the em-dash gives it an extra dramatic flair.