Hyphens and Dashes

Learning Objectives

  • Demonstrate the proper use of hyphens and dashes

Hyphens

Appropriate alternative text for this image can be found in the caption.

Figure 1. A hyphen.

The Oxford Manual of Style once stated, “If you take hyphens seriously, you will surely go mad.” Hyphens belong to that category of punctuation marks that will hurt your brain if you think about them too hard, and, like commas, people disagree about their use in certain situations. Nevertheless, you will have to use them regularly because of the nature of academic and professional writing. If you learn to use hyphens properly, they help you to write efficiently and concretely.

The Hyphen’s Function

Fundamentally, the hyphen is a joiner. It can join several different types of things:

  • two nouns to make one complete word (kilogram-meter)
  • an adjective and a noun to make a compound word (accident-prone)
  • two words that, when linked, describe a noun (agreed-upon sum, two-dimensional object)
  • a prefix with a noun (un-American)
  • double numbers (twenty-four)
  • numbers and units describing a noun (1000-foot face; a 10-meter difference)
  • “self” words (self-employed, self-esteem)
  • new word blends (cancer-causing, cost-effective)
  • prefixes and suffixes to words, in particular when the writer wants to avoid doubling a vowel or tripling a consonant (anti-inflammatory; shell-like)
  • multiple adjectives with the same noun (blue- and yellow-green beads; four- and five-year-olds)

A rule of thumb for the hyphen is that the resulting word must act as one unit; therefore, the hyphen creates a new word that has a single meaning. Usually, you can tell whether a hyphen is necessary by applying common sense and mentally excluding one of the words in question, testing how the words would work together without the hyphen. For example, the phrases “high-pressure system,” “water-repellent surface,” and “fuel-efficient car” would not make sense without hyphens, because you would not refer to a “high system,” a “water surface,” or a “fuel car.” As your ears and eyes become attuned to proper hyphenation practices, you will recognize that both meaning and convention dictate where hyphens fit best.

Examples of Properly Used Hyphens

Some examples of properly used hyphens follow. Note how the hyphenated word acts as a single unit carrying a meaning that the words being joined would not have individually.

small-scale study two-prong plug strength-to-weight ratio high-velocity flow frost-free lawn
self-employed worker one-third majority coarse-grained wood decision-making process blue-green algae
air-ice interface silver-stained cells protein-calorie malnutrition membrane-bound vesicles phase-contrast microscope
long-term-payment loan  cost-effective program  time-dependent variable radiation-sensitive sample  long-chain fatty acid

When Hyphens Are Not Needed

By convention, hyphens are not used after words ending in –ly, nor when the words are so commonly used in combination that no ambiguity results. In these examples, no hyphens are needed:

finely tuned engine blood pressure sea level
real estate census taker atomic energy
civil rights law public utility plant carbon dioxide

Note: Phrases like containing the word well like well known are contested. Well is an adverb, and thus many fall into the school of thought that a hyphen is unnecessary. However, others say that leaving out the hyphen may cause confusion and therefore include it (well-known). The standard in MLA is as follows: When it appears before the noun, well known should be hyphenated. When it follows the noun, no hyphenation is needed.

  • She is a well-known person.
  • She is well known.

Prefixes and Suffixes

Most prefixes do not need to be hyphenated; they are simply added in front of a noun, with no spaces and no joining punctuation necessary. The following is a list of common prefixes that do not require hyphenation when added to a noun:

after anti bi bio co
cyber di down hetero homo
infra inter macro micro mini
non photo poly stereo thermo

When prefixes are added to a proper noun, they require a hyphen (e.g., nonviolent, but non-European).

Note: The prefix re generally doesn’t require a hyphen. However, when leaving out a hyphen will cause confusion, one should be added. Look at the following word pairs, for example:

  • resign (leave a position) v. re-sign (sign the paper again)
  • recreation (an activity of leisure) v. re-creation (create something again)

Common suffixes also do not require hyphenation, assuming no ambiguities of spelling or pronunciation arise. Typically, you do not need to hyphenate words ending in the following suffixes:

able less fold like wise

Commonly Used Word Blends

Also, especially in technical fields, some words commonly used in succession become joined into one. The resulting word’s meaning is readily understood by technical readers, and no hyphen is necessary. Here are some examples of such word blends, typically written as single words:

blackbody groundwater airship
downdraft longwall upload
setup runoff blowout

Try It

Dashes

Appropriate alternative text for this image can be found in the caption.

Figure 2 . An em dash.

The dash functions almost as a colon does in that it adds to the preceding material, but with extra emphasis. Like a caesura (a timely pause) in music, a dash indicates a strong pause, then gives emphasis to material following the pause. In effect, a dash allows you to redefine what was just written, making it more explicit. You can also use a pair of dashes in place of parentheses, to frame an interruptive or parenthetical-type comment that you do not want to de-emphasize.

  • Jill Emery confirms that Muslim populations have typically been ruled by non-Muslims—specifically Americans, Russians, Israelis, and the French.
  • The dissolution took 20 minutes—much longer than anticipated—but measurements were begun as soon as the process was completed.
There is no “dash” button on a computer keyboard. Instead, create it by typing the hyphen button twice in a row; or use the “symbol” option in your word processor; or use the Mac shortcut option + shift + —.
Appropriate alternative text for this image can be found in the caption.

Figure 3. An en dash.

The Em-dash

The dash we typically use is technically called the “em dash,” which gets its name from back in the days of typesetting on old-fashioned printing presses. It is a dash that is the width of an M, so it is significantly longer than the hyphen.

The En-dash

There is also an “en dash”—whose length is that of an N, between that of the hyphen and the em dash, and its best usage is to indicate inclusive dates and numbers:

  • July 6–September 17
    • The date range began on July 6 and ended on September 17.
  • Barack Obama (1961–)
    • This indicates the year a person was born, as well as the fact that he or she is still alive.
  • pp. 148–56
    • This indicates pages 148 through 156. With number ranges, you can remove the first digit of the second number if it’s the same as the first number’s.

The en dash can also be used for flight or train routes.

  • The London–Paris train will be running thirty minutes late today.
Like the em dash, the en dash is not on the standard computer keyboard.  Select it from word processor’s symbol map (or if you have a Mac, you can type option), or it may even be inserted automatically by your word processor when you type inclusive numbers or dates with a hyphen between them. In most contexts, a hyphen can serve as an en dash, but in professional publications—especially in the humanities—an en dash is correct.

When you type the hyphen, en dash, and em dash, no spaces should appear on either side of the punctuation mark.

Try It

Click through this presentation and answer the questions to test your understanding of when to use dashes and hyphens.

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