How to Use an Em Dash
The em dash (the longest of the three types of dash) is a useful piece of punctuation, but it’s often misused (though not as much as commas) and not typographically rendered correctly. In this post, I’ll discuss how to use an em dash and how to correctly format it in your text. Also, all my examples in this post are space-themed, so buckle up!
What is an Em Dash?
In my first ever copy editing and proofreading course, I was shocked to learn that there are three types of dash in English. I’m not going to go into detail about all three of them here, but just know that there is the hyphen (the short one that connects words), the en dash (a little bit longer than the hyphen and often appears between numbers), and the em dash (the longest of the bunch).
The em dash is so named because it was the length of the letter M on old-fashioned typewriters. On your web browser, it looks like this: — (as opposed to the hyphen, -, and the en dash, –).
What the Em Dash Does
The em dash acts as an interrupter and draws emphasis to what comes next. Em dashes can be used to introduce something in the middle or at the end of the sentence:
Kepler 186f—discovered in 2016—is over 500 light years from Earth.
Kepler 186f is over 500 light years from Earth—and may be capable of hosting life.
Em dashes are particularly helpful if you encounter a situation in which using commas would be confusing. Consider the following example:
Mars, which has comparatively low gravity, a thin atmosphere, and no magnetic field, is a target for human colonization.
All those commas make it difficult to pick out the main clause of the sentence (“Mars is a target for human colonization”). In other words, the non-essential (or parenthetical) element of the sentence is not immediately clear. This is where the em dash comes in:
Mars—which has comparatively low gravity, a thin atmosphere, and no magnetic field—is a target for human colonization.
Replacing the first and last comma with em dashes makes clear where the main clause pauses and picks up again.
The em dash can also be helpful to set off what otherwise would act as a sentence fragment:
The meteor exploded into several pieces that ignited upon contact with the atmosphere. Stunning, to say the least.
That last part—“Stunning, to say the least”—is a sentence fragment. Depending on the context and the kind of writing you’re doing, sentence fragments may or may not be acceptable. In either case, it’s best to keep them to a minimum. Using an em dash is a pain-free way of incorporating fragments into a sentence:
The meteor exploded into several pieces that ignited upon contact with the atmosphere—stunning, to say the least.
How to Render Em Dashes
This depends on what program you’re using. I’m going to talk about Microsoft Word, because that is, by far, the most common word-processing program used for revisions and constructing manuscripts.
The easiest way to make an em dash is with unicode. Simply type “2014” into your manuscript. Then, with the text cursor right after the “4,” hit ALT+X. Poof. An em dash will appear in place of the numbers.
In North American English, we don’t put spaces on either side of the em dash (like I’ve done in all the above examples). In British English, however, the em dash often appears with spaces around it (like this: this is — an em dash). This practice seems to be growing less common, however. Oxford Dictionary now recommends closing up em dashes as in North American English.
So there you have it—a handy guide on how to use an em dash. Em dashes are versatile and can help your reader visualize parts of the sentence more easily. However, I caution you against overusing them. Em dashes, like semicolons, derive their impact largely from their relative scarcity in the text. Including too many em dashes can distract your reader. So use em dashes, but save them for when they can have the most effect!