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.

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)

Tip: 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 you become attuned to proper hyphenation practices, you will recognize where hyphens fit best.

Examples of Properly Used Hyphens

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. So, for example, above, we use no hyphen when discussing properly used hyphens.

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. So, for example, above, we use no hyphen when discussing properly used hyphens.

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 containing the word well like well known are contested. Well is an adverb (like finely and other adverbs that typically end in -ly). Thus many think a hyphen is unnecessary with well known. Others say that leaving out the hyphen may cause confusion and 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.
  • The actor in the series is a well-known bodybuilder.
  • She is well known.
  • As she becomes more well known, her Instagram following will probably increase.

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

Ambiguities of spelling or pronunciation are exceptions.

Her face is bell-like. (Using an “l” three times in a row would be messy).

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 (like a colon) to add emphasis to the preceding material.  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 em dash here gives extra emphasis to the examples of non-Muslims (American, 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. (The pair of em dashes here work like parentheses to add emphasis to the fact that 20 minutes was much longer than anticipated.)
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 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 it’s best used with 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 the former president was born as well as the fact he 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.

Notice the en dash and numbers. 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.