Happy National Punctuation Day!

National Punctuation Day is celebrated on September 24 in the US, and it is also recognized in other countries such as Canada. In honor of this language-related holiday, I decided to write about punctuation!

The em dash is fairly common in printed materials and online, but neither English speakers nor learners are usually taught how to use this symbol. I certainly can't recall ever teaching it to my students. Only when I was studying to become an editor did I fully learn the correct usage. I'll share what I've learned in the hopes that both teachers and students will benefit!

What is an em dash?

An em dash is an elongated hyphen (about the length of three hyphens) that is used for specific purposes. Here’s how the dash family looks:

What is the em dash used for?

The em dash is used primarily for joining phrases or clauses together instead of a semicolon, colon, commas, or parentheses. Its purpose is to set some information apart as an explanation or elaboration. It is also used for emphasis.

Examples:

• She was worried about him—he didn’t seem very happy. (explanation, used instead of a semicolon)
• It’s that time of year again—time to cram for final exams. (explanation, used instead of a colon)
• The kiwi bird—a flightless, nocturnal bird—is only native to New Zealand. (elaboration, used instead of commas or parentheses)
• Three of my friends—Sarah, Michelle, and Tracy—are coming to my party. (elaboration, used instead of commas or parentheses)
• His new car—and what a car!—was a Lamborghini. (emphasis, used instead of parentheses)

How did the em dash get its name?

The em dash got its name from the olden days of typesetting. Back before the computer era, when publishers wanted to use this dash, they would make it the same length as the “m” character length of the typeset block. In most modern fonts, too, the em dash is the same length as the letter “m” or “M.”

Where can you find it on your computer?

The em dash is easy to make using keyboard shortcuts. On a Mac, hold down shift + option + hyphen. On a PC, hold down the Alt key and type 0151.

Should there be spaces around the em dash?

Though it is optional, it seems like the slight majority of people choose not to put spaces around the em dash. Some style guides, such as the Chicago Manual of Style, agree.

Examples:

• Three of my friends—Sarah, Michelle, and Tracy—are coming to my party. (without spaces)
• Three of my friends — Sarah, Michelle, and Tracy — are coming to my party. (with spaces)

I suggest teaching students not to use spaces since this is a little more common. For more advanced students, you can tell them that it is optional, and challenge them to find examples of both in printed materials or online.

For editors, it depends on the company's house style. Check the style guide that the company uses to see what’s recommended. At ESL Library, for example, we don’t use spaces.

Source: The Chicago Manual of Style, 16^th edition, sections 6.82–6.89.