How (and why) to use em-dashes

Em-dashes are among the most useful but underused punctuation marks.

Mar 29, 2021

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When you are writing longer sentences, keep the reader’s short-term memory and mental energy in mind. Help the reader absorb information in manageable chunks by using punctuation to break the sentence into parts. The em-dash ( — ) is particularly useful for this task.

Em-dashes, en-dashes, and hyphens

At the outset, you should learn to recognize the difference between em-dashes (—), en-dashes (–), and hyphens (-). En-dashes are used primarily for numeric ranges (e.g., “March 15–20” and “pp. 159–61”).

When to use an em-dash

Here are three common uses of em-dashes:

Use an em-dash to set off and emphasize a parenthetical phrase. (For this purpose, em-dashes are more emphatic than parentheses or commas.)

Example:

First-year law students read judicial opinions as they read most other material — from beginning to end — but experienced lawyers often jump straight to the rule.

Use em-dashes to set off a phrase that modifies or explains something in the middle of the sentence.

Example:

This year’s 2Ls — many of whom have had their plans disrupted by COVID-19 — are even more concerned about grades than usual.

Use em-dashes to add an afterthought to a sentence.

Example:

I read War and Peace this summer — all 1,200 pages of it.

How to create em-dashes

Sadly, keyboards do not normally include an em-dash key. Here are three ways to create em-dashes (which are sometimes referred to simply as “dashes”):

In Microsoft Word, type a letter immediately followed by two hyphens and then another letter, as in “a--b.” The two hyphens should automatically expand into an em-dash.
In Word or other text-editing programs, create a keyboard shortcut such as Ctrl + Alt + M that inserts an em-dash. In my version of Word, you can accomplish this by visiting Insert > Advanced Symbol > Special Characters. Then, highlight “Em Dash” and click “Keyboard Shortcut.”
Use a text expansion program such as aText or PhraseExpress to create a text snippet that expands into an em-dash. For example, when I type “emd” with aText running, those letters are immediately replaced by an em-dash.

Note that Macs and iOS devices have built-in text expansion. To set up text snippets, visit System Preferences > Keyboard > Text.

A caveat about overuse

Note that em-dashes create emphasis by forcing the reader to pause. Be careful not to overuse them. I recommend sticking to a maximum of one em-dash or pair of em-dashes per paragraph, and no more than a handful per page.

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Ryan McCarl (LinkedIn | Twitter | Blog) teaches Advanced Legal Writing at the UCLA School of Law and is a partner at the law firm Rushing McCarl.