4.9: Dashes and Hyphens

Figure \(\PageIndex{1}\)

Hyphens

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.

Table \(\PageIndex{1}\): Examples of 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. In these examples, no hyphens are needed:

Table \(\PageIndex{2}\): Examples when Hyphens are not 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:

Table \(\PageIndex{3}\): Common prefixes that do not require hyphenation when added to a noun

After	Anti	Bi	Bio	Co
Cyber	Dl	Down	Hetero	Homo
Infra	Inter	Macro	Micro	Mini
Nano	Photo	Poly	Stereo	Thermos

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:

Table \(\PageIndex{4}\): Examples of Common suffixes that do not require hyphenation

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:

Table \(\PageIndex{5}\): Examples of word blends

Blackbody	Groundwater	Airship
Downdraft	Longwall	Upload
Setup	Runoff	Blowout

Dashes

Figure \(\PageIndex{2}\): 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 dash as it is used in the first sentence of this paragraph: 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 + —.

The dash we typically use is technically called the “em dash,” and it is significantly longer than the hyphen. There is also an “en dash”—whose length is between that of the hyphen and the em dash, and its best usage is to indicate inclusive dates and numbers:

Figure \(\PageIndex{3}\): "en dash"

• 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.

It 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.

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