The hyphen, the em dash and the en dash are the straight arrows among punctuation marks, an otherwise fairly curvaceous lot. The hyphen (-), the shortest of the three marks, is familiar (sometimes wretchedly so) to most writers. So is the em dash (—), more often called the long dash, or sometimes just the dash. The middle-length en dash (–) is the most mysterious of the three. Known mainly to editors, printers and desktop publishers, the en is surprisingly easy to use once you understand its purpose.

Hyphens

Know someone who thinks hyphens don’t matter? Show them this headline and its accompanying text:

A single misplaced hyphen and the reader expects destructive frogs instead of a deadly fungus.

The hyphen, which shares a key with the underscore mark on the standard keyboard, has several functions. It punctuates phone numbers, ISBN codes on books and other strings of numerals. It divides words at the end of lines in typeset material. And most commonly, as in the headline above, it glues together compound structures.

Herein lies the hyphen’s beauty, and its perversity. Why do people sign up for things on a sign-up sheet? How can someone wear a tight-fitting skirt and a tightly woven scarf? Why is a well-tailored suit well tailored? And a long-term plan a scheme for the long term?

The guidelines for compounding with hyphens fill eleven pages in The Canadian Style (2nd ed., 1997), twelve in The Chicago Manual of Style (16th ed., 2010). No wonder John Benbow, former editor of the Oxford University Press stylebook, once warned, "If you take hyphens seriously, you will surely go mad." Still, there are some general principles. For instance, a hyphen often joins a compound modifier when the modifier precedes the word described, but not when it follows it.

• on-site facilities
• facilities on site

• his well-received debut
• his debut was well received

One important exception occurs when the first part of the compound modifier is an adverb ending in -ly. Such compounds never take hyphens.

• a widely criticized notion
• thoroughly disreputable behaviour

A compound verb made up of a verb plus an adverb or a preposition is normally not hyphenated. But when the compound serves as an adjective or a noun, it is.

• run on at the mouth (verb)
• a run-on sentence (adjective)

• follow up the meeting (verb)
• a follow-up meeting (adjective)

• sing along with me (verb)
• a sing-along (noun)

A good dictionary and a reliable style guide are indispensable aids for navigating the labyrinth of hyphen use. When in doubt, remember that hyphens exist primarily to help readers get the meaning. If you need a hyphen for clarity, leave it in. A compound missing its hyphen can perplex and befuddle.

• a small armed man (a man who should build his biceps? or one who is puny and carrying weapons?)
• the worst paying jobs (the jobs that pay the worst? or the worst of the paying jobs?)

Em dashes

The em dash—so called because in traditional typesetting it was the length of a capital M—is often known by its more pedestrian, non-alphabetical name, the long dash. In the bygone days of typewriters, the em dash was rendered as two hyphens (--), but today modern word processing packages offer a genuine em dash in their special character sets.

The em is an expansive, attention-seeking dash. It supplies much stronger emphasis than the comma, colon or semicolon it often replaces. Positioned around interrupting elements, em dashes have the opposite effect of parentheses—em dashes emphasize; parentheses minimize.

• Rayna has said that she will help with the play—but not direct it—in the coming months.
• Rayna has said that she will help with the play (but not direct it) in the coming months.

Em dashes set off interruptions that are too abrupt or lengthy to be set off by commas, as well as interruptions that already contain commas.

• When you vote for me—and I know you will—please remember that I have promised nothing, and I will deliver what I promise. (abrupt)
• Four tragedies—Hamlet, Macbeth, King Lear and Othello—are generally considered among Shakespeare’s best plays. (lengthy, contains commas)

An em dash can focus or summarize a list of elements. It can also mark a sharp turn in thought.

• Chocolate, cream, honey, peanut butter—all go into this fabulously rich dessert. (focuses a list)
• He praised Ann’s intelligence, her warmth, her good taste—and then proposed to her sister. (marks a sharp turn)

A word of warning: because em dashes are so emphatic, use them sparingly. Some writers latch on to dashes, stretching their prose with them until the reader is positively breathless. It’s best to heed the counsel of John Wilson, author of the Victorian-era Treatise on English Punctuation: "[T]he unnecessary profusion of straight lines, particularly on a printed page, is offensive to good taste, is an index of the dasher’s profound ignorance of the art of punctuation . . . ."

En dashes

Despite its name, the en dash has more in common with the hyphen than with the em dash. In fact, it helps to think of the en dash, which is half the length of the em, as a variant of the hyphen.

The en dash, which like the em is supplied in word processing character sets, mainly joins inclusive numerals, between which the word to is intended.

• chapters 13–24
• 25–50 MP3 players
• pages 3–8
• the 1986–87 term

The en dash also attaches a prefix or suffix to an unhyphenated compound.

• post–World War I treaty
• New York–based writer
• non–sodium chloride solution
• sodium chloride–free solution

And often the en dash joins the names of two or more places.

• the Calgary–Vancouver route
• the constituency of Hull–Aylmer

The long and the short of it

Similar in appearance yet disparate in function, hyphens, em dashes and en dashes are essential marks. Follow these guidelines and a reliable style manual, and you’ll have little trouble keeping them straight.

Test yourself