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:
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:
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:
- No one believed Hikaru when he said he was (self taught/self-taught) because his skills necessitated the presence of a teacher.
- Jean promised to drop the boys off at the (railroad/rail-road) station.
- Roy and Riza were very tired after the (three hour-long/three-hour-long/three-hour long) PTA meeting.
- Eli was pleased to see that he still had a (four or five-point/four- or five-point) lead on his opponent
- No one believed Hikaru when he said he was self-taught because his skills necessitated the presence of a teacher.
- Jean promised to drop the boys off at the railroad station.
- Roy and Riza were very tired after the three-hour-long PTA meeting.
- Eli was pleased to see that he still had a four- or five-point lead on his opponent.
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.
When you type the hyphen or dash, no spaces should appear on either side of the punctuation mark.
Is the dash used correctly in the following sentences?
- Fifty people will be coming to the potluck on Thursday—at least that’s what the survey said—so we should be sure to bring a lot of sandwiches.
- A balanced meal should always include—proteins, vegetables, and carbohydrates.
- I know I missed the last several meetings, but I won’t sleep through this one—honestly!
- We convinced our teacher that we needed a field trip—who knows how—so we’re all going to a publishing company on Thursday.
- Correct. This dash marks a sudden break in thought.
- Incorrect. The examples should be preceded by a noun: A balanced meal includes several different food groups—proteins, vegetables, and carbohydrates.
- Correct. This dash connects an affirmation to the initial thought.
- Correct. This is another break in thought, and is still correct even though the comment is not very strongly related to the rest of the sentence.