6.5 Hyphens, En Dashes, & Em Dashes

Image of punctuation marks: hyphen, em dash, and en dash

“Dashes” by Aptiva, is licensed CC0 1.0 Universal Public Domain

According to the style manual of the Oxford University Press, “If you take hyphens seriously, you will surely go mad.”[1]

Hyphens are supposed to keep us from misreading things and show us how words in complex phrases relate to each other. The problem is that the rules for hyphens just cannot be applied absolutely consistently—you end up hyphenating everything, including the-kitchen-sink. (*Note: that hyphenation is incorrect.) Professional editors keep long lists of exactly which word pairs they will hyphenate in a specific document (so they don’t end up in therapy).

Hyphens do matter, however. Our language culture seems to encourage piling up ambitious noun phrases. These sentences verge on having a problem called noun stacks or noun strings. To read this kind of stuff, we need hyphens—they show us what goes with what. Hyphens show that a pair of words is acting as a unit, perhaps as an adjective or a compound noun, and must be read as one thing. The common types of unit modifiers—which are two or more words acting as a unit—are discussed in this section, but this is by no means exhaustive coverage of the topic. Different organizations have different in-house rules and style guides that specify their preferences regarding hyphenation. Consult the appropriate style guide when you are writing for an organization that has one. But below are a few general guidelines.

do not hyphenate the common prefixes such as pre, anti, multi, and so on

(Unless failing to do so spells some other word or just looks hopelessly weird)

  • prehistoric
  • pre-exist
  • reusable
  • re-sent
  • antisocial
  • anti-icing

hyphenate prefix words (such as self-)

  • self-lubricating hinges
  • mid-1970s
  • micro-universe

Hyphenate a unit modifier

The unit in these examples is made up of a number followed by a unit of measurement.

  • 5-year grant
  • 10-month period
  • 28-gigabyte memory
  • 8-oz. cup
  • 4-gallon tub

Hyphenate two words that act as a unit to modify another word

Compound modifiers require hyphens. (Often these are acting as adjectives.)

  • below-average rainfall
  • warm-up period
  • on-board timer

  • pay-off period

They may include a non-verb element and a verb-like element acting as a unit.

  • drought-producing system
  • water-repellent fabric
  • coffee-flavored ice cream
  • government-sponsored programs

 

Watch out for three or more words acting as a unit to modify a noun

Think of the three words as one unit, connected by hyphens.

  • a case-by-case basis
  • a three-to-one ratio
  • the right-to-die statutes
  • the air-to-ground voice transmission
  • on-the-job experience

Don’t hyphenate units in which the first word ends in -ly.

  • highly developed country
  • fully equipped computer

The toughest area for hyphenation are those combinations that look like:

adjective + noun + noun

noun + noun + noun

If the initial adjective or noun modifies the final noun, do not use a hyphen.

  • embryonic stem cells
  • poor economic performance

If the initial adjective or noun modifies the noun directly following it, consider using a hyphen.

  • cell-replacement strategies
  • cell-surface markers
  • big-name automakers
  • large-scale production

If you are in doubt about whether to use a hyphen, don’t use it. The recent trend is away from hyphenation and, over time, many words that are originally written using hyphens gradually shake off the hyphenation to become single words. A solid resource on hyphens is Garner’s Modern English Usage; see “Phrasal adjectives.”

Once you get a partial feel for hyphens, watch out! Everything will seem like it needs a hyphen! When that happens, back off and ask yourself—could someone misread this sentence without a hyphen? If the sentence won’t be misread, give your hyphen key a break.

Be sure to note the difference between a hyphen and an em dash or an en dash. When you are separating a chunk of text within a sentence—such as this phrase—a hyphen is not the correct punctuation mark. You need an em dash instead. An em dash is a dash that is the same as the length of a particular font point size. If you are using 12-point font, the em dash in that font will be 12 points wide. An en dash is slightly less wide than an em dash (but longer than a hyphen) and is used to indicate ranges, such as scores, pages, and dates.

Read pages 274–298. (en dash)

The Yankees beat the Rangers 7–4. (en dash)

Here’s what the different marks look like:

hyphen-

en dash –

em dash —

Using these punctuation marks—the hyphen, the em dash, and the en dash—correctly brings a level of professionalism to your writing and makes it easier for your readers to understand the text.


  1. “Hysteria over Hyphens.” The Economist, The Economist Newspaper, 8 June 2017, http://www.economist.com/books-and-arts/2017/06/08/hysteria-over-hyphens.