49 Hyphens and Dashes
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.
| 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