Dashes and hyphens are so often considered together that when I got to the end of “Sturgis’s Law #10,” I knew something was missing. After all, the Chicago Manual of Style (CMS) devotes several pages to dashes, and so do many other style guides. Surely I should devote at least a few words to the subject?

But I’d already gone on too long (blog posts that top 1,000 words make me nervous), and besides, nowhere in Sturgis’s Laws are dashes even mentioned. (That may change in the future.)

Meanwhile — let’s talk about dashes.

In U.S. usage, dashes come in two sizes. The em dash ( — ) is so called because it’s generally the length of one m. The shorter en dash (which, surprise surprise, is the length of an n) is the one that gets mixed up with hyphens.

As my typographer friends point out, a dash is a dash. How it’s styled — em or en, with or without space before and after — is a typographical decision. In British English (BrE) the kind of dash that indicates a break or sets off parenthetical remarks (as in the previous sentence) is generally rendered by an en dash with a space on either side, like this: How it’s styled – em or en, with or without space before and after – is a typographical decision.

• To create an em dash on a PC: Alt+0151 (use the number pad) or ALT+CTRL+minus key (the latter works in Word but not in WordPress). Using AutoCorrect, you can also tell Word to automatically convert two hyphens (which is how we indicated em dashes back in typewriter days) to an em dash. I don’t allow Word to AutoCorrect anything, but you may be more tolerant than I.
• To create an en dash on a PC: ALT+0150 or CTRL+minus key (see above)
• To create an em dash on a Mac: Option+Shift+minus
• To create an en dash on a Mac: Option+minus

In this blog and in my own writing, I insert a space on either side of my em dashes. This is to avoid bad end-of-line breaks. Word processors may treat “styled—em” in the sample sentence as one word and keep it all on one line, which may lead to an unsightly gap in the line preceding. The shorter dash seems to be coming into its own in ebooks, and with good reason: ebooks can be read on devices with relatively narrow lines, and in a narrow line a full em dash can look huge.

Em dashes generally herald a break of some kind. In dialogue, they are commonly used to indicate in interruption: “But I was about to say—” Frankie began before Sal cut her off. (Dialogue that trails off is generally indicated by an ellipsis. For more about this see “Of Dots and Dashes.”)

In non-dialogue, they can signal a change of subject or an aside. When the aside occurs in the middle of a sentence, it becomes more or less a parenthetical and is set off by em dashes. Why not use parentheses in such cases? You can use parens in such cases. For me an aside set off by parens is more peripheral — expendable, even — than one set off by dashes.

Em dashes are big. They call attention to themselves. Flip through a book — on paper or on screen — and chances are your eye will be drawn to the em dashes. If a writer is overusing em dashes, it’s often the first thing I notice when skimming through a manuscript. So use them sparingly. Like just about everything else in writing, they lose their power when overused.

Emily Dickinson is noted for her extravagant use of dashes, but she could get away with it because (1) she was a poet, (2) her poetry was brilliant, and (3) she was writing in the 19th century, before the Chicago Manual of Style was invented. Long after she died, one of her editors got into big trouble for taming her dashes into commas. If you’re adding Dickinson’s collected poems to your library, make sure the edition you choose has the dashes.

En dashes are somewhat specialized, and different styles have different takes on when to use them. In the social sciences, for instance, an en dash is often used to indicate that a compound comprises two words of equal weight, e.g., “I’m a writer–editor.” Chicago does not recommend this, and neither do I. Here’s my reasoning: The difference in length between a – and a – is not huge. When you’re reading along, you may not notice it at all — unless of course you’re a copyeditor like me. If it is important to know that the two halves of a compound are of equal weight, I would not depend on an en dash alone to get that across. However, if you’re in a field that follows this style, you should too.

Here are the most common uses of en dashes, per Chicago:

• To signify through in number ranges: pages 3–17; the years 1941–1945. The range can be open-ended: my dog Travvy (2008–).  Figures and tables in nonfiction books are often given numbers like 2-5 and 3-17. The hyphen denotes that this is NOT a range; the first number is generally that of the chapter and the second that of the particular figure or table. The distinction comes in handy in footnotes and endnotes, where page ranges run rampant and table and figure numbers are sometimes concealed among them. By the way, It’s a faux-pas to use the dash when the range is preceded by from: She lived in France from 1978 to 1982, not “from 1978–1982.”
• To signify to in destinations, votes, or scores: the Boston–Washington train; my team won, 99–92; the vote was 5–4.
• To form compounds when one element is itself an open compound: the post–World War II baby boom; the New York–Boston rivalry. This is to avoid reading the former as post-world and the latter as York-Boston. Editors sometimes differ on which open compounds have to stay open and which can be hyphenated when attached to prefix, suffix, or another word. Proper nouns generally stay open, but when the New-York Historical Society was founded in 1804 another style prevailed, and its official name is so styled to this very day. Chicago 16, section 6.80, recommends country music–influenced lyrics, but I see nothing wrong with country-music-influenced lyrics.

All clear now? Dash away, dash away, dash away, all. And I really should come up with a dashing Sturgis’s Law . . .