Use a hyphen (-) to form compounds of two or more words and to separate some prefixes and suffixes from root words.
Forming compound modifiers
A compound modifier is two or more words that function as a unit. For compound modifiers that come before a noun, use hyphens to join the parts of the compound so that readers understand your intent. Consider the difference, for example, between red and green ties and red-and-green ties.
When faced with a compound modifier, follow these rules:
- Use a hyphen or hyphens for compound adjectives preceding a noun. (For more on compound adjectives that include a number, see “The Basics.”)
Don’t use a hyphen for compounds including more, less, most, or least unless the compound could be misread.
The email campaign had a better-than-average response.
Take advantage of the 30-day free trial.
The more logical solution is to begin at the beginning.
Her debut single was the most downloaded song of 2009.
Researchers then eliminated less productive plants to favor those with a high yield.
- Use a suspended hyphen (a hyphen followed by a space) when the second element of the first compound modifier is omitted. The second element of the second compound modifier must appear before the noun. (This assumes there are only two compound modifiers).
We heard pro- and anti-IMF speeches.
Both the French- and Chinese-speaking participants had excellent interpreters.
Any class is going to have both under- and overachieving students.
- Don’t use a hyphen or hyphens if a compound modifier follows a noun, unless the modifier comes after a form of the verb to be (like is, are, was, were).
Certain compound modifiers don’t need hyphenation even after a form of the verb to be. These include:
- Adjective + infinitive: easy to use, harder to learn, ready to eat
Note: The infinitive is the to form of a verb.
- Adjective + prepositional phrase: fresh from the field, hot off the grill
- Adjective + than or as comparison: better than average, bland as oatmeal
- Adverb + past participle + preposition: often referred to, much talked about
The well-behaved dog won first prize.
He was well-behaved.
Positive reinforcement made him well behaved.
Sign up now for our trouble-free service.
The service is trouble-free.
It’s an easy-to-use tool.
The tool is easy to use. (Adjective + infinitive exception)
Sample our fresh-from-the-field produce.
Our produce is fresh from the field. (Adjective + prepositional phrase exception)
Her redder-than-red face betrayed her embarrassment.
Her face was redder than red. (Adjective + “than” exception)
This is an often-referred-to section.
This section is often referred to. (Adverb + past participle + preposition exception)
- Don’t use a hyphen following the adverb very and adverbs ending in ly. Very or an -ly adverb clearly modifies the following adjective, so no hyphen is needed to avoid confusion. (But note that not all -ly words in compound modifiers are adverbs. You can tell when an -ly word is not an adverb because the word following the -ly word cannot stand alone without changing the meaning.)
a very exciting product
a completely new production (You can have a “new production.”)
a scholarly-looking girl (You cannot have a “looking girl.”)
When a compound modifier contains punctuation or is too long to string together with hyphens, use quotation marks—for examples, see “Quotation Marks.”
For information about capitalizing compound modifiers, see “Hyphenated compounds in title case” under “Capitalization.”
Joining prefixes and suffixes
Because dictionaries take different approaches to spelling and hyphenation, you and your organization should rely on one primary dictionary to determine which words require hyphenation. A number of Web publications use Dictionary.com, choosing the entries provided by the Random House Dictionary or the American Heritage Dictionary of the English Language. Some use Merriam-Webster Online, which is based on Merriam-Webster’s Collegiate Dictionary. Others use YourDictionary.com, which provides entries from Webster’s New World College Dictionary.
Decide whether to apply blanket rules for all prefixes and suffixes or whether to apply your rules only if a word is not listed in your dictionary. (Either decision is fine; just be consistent. Record your decision in your style guide and include any exceptions in your word list.)
For prefixes, you may want to follow these guidelines:
- Generally, close up prefixes with root words: antiviral, transcontinental.
- Hyphenate to avoid a doubled vowel (for example, two o’s together).
- Insert a hyphen after co- when it designates a shared occupation or status.
- Insert a hyphen after e- when it stands for electronic (exception: email).
- Insert a hyphen if the root word is capitalized.
- Insert a hyphen before a numeral.
- Hyphenate doubled prefixes.
semi-invalid (Hyphen to separate doubled vowel)
co-author (Hyphen for “co-” indicating shared occupation)
e-commerce (Hyphen for “e-” when it stands for “electronic”)
email (Exception: No hyphen in “email”)
pan-Asian (Hyphen to separate capitalized root word)
mid-20th century (Hyphen to separate numeral)
re-reunification (Hyphen to separate doubled prefix)
- Make sure that the prefix is attached to all parts of the phrase it applies to.
anti-child-pornography law (Not “anti-child pornography law”)
The guidelines for suffixes are simpler:
- Insert a hyphen to avoid a doubled consonant.
- Insert a hyphen to avoid a hard-to-read result.
- Insert a hyphen after a capitalized noun.
flowerlike, daffodil-like, hippopotamus-like, Renoir-like
nationwide, pew-wide, university-wide, Seattle-wide
Use a hyphen when omitting it might lead to a misreading.
I resent that message.
I re-sent that message. (Perhaps I resent the message as well, but I am keeping my feelings to myself.)
They then heard more unbelievable stories. (Are the stories more unbelievable than the ones previously told, or are there simply more of them?)
They then heard more-unbelievable stories. (The stories are more unbelievable.)
They then heard stories more unbelievable than the last.