Punctuation marks, as a convention of written language, function to ensure the clarity of writing for readers and writers. There are seven rules for using hyphens as punctuation marks in written American English:
- With affixes
- In compound nouns
- In coequal nouns
- In compound modifiers
- In phrasal modifiers
- In numbers
- To avoid confusion and misreading
The following sections explain and provide examples of the punctuation rules for hyphens in written English.
Use a hyphen between certain prefixes and suffixes such as all-, anti-, -elect, ex-, mid-, neo-, non-, post-, pre-, pro-, and self- and a noun. For example:
Use a hyphen between the prefixes anti-, mid-, neo-, post-, pre-, and pro- and a proper noun or number. For example:
Usually use a hyphen between a prefix and a noun when the last letter of the prefix is the same as the first letter of the noun. For example:
Do not use a hyphen with most other prefixes and suffixes. When in doubt, check a dictionary for standard hyphen use.
Use a hyphen in some compound nouns. For example:
When in doubt, consult a dictionary to determine if a compound noun requires a hyphen.
Use a hyphen to join two or more coequal nouns. Coequal nouns are defined as pairs of nouns that are equal in function. For example:
Do not use a hyphen to join two or more nouns in which the first noun functions as a noun phrase modifier of the second noun.
Use a hyphen to join compound noun phrase modifiers that precede a noun especially when (1) adverbs such as better, best, ill, lower, little, and well modify an adjective, (2) the second word is a present participle or past participle of a verb, and (3) the compound modifier contains a number. For example:
- blue-collar worker
- self-fulfilling prophecy
- ill-prepared student
- well-behaved toddler
- forth-floor office
- sports-hating aunt
Do not use a hyphen to join compound noun phrase modifiers that follow the noun. Also do not use a hyphen to join an adjective to an adverb ending in -ly or to the adverbs too, very, or much.
Use a hyphen to separate words in a phrase that is functioning as a noun phrase modifier that precedes a noun. For example:
- The cruise ship offers an all-you-can-eat seafood buffet.
- Childbirth can be an out-of-this-world experience.
- My doctor prescribed me an over-the-counter medication.
- He has a stronger-than-he-looks outlook on life.
Use a hyphen in the number between twenty-one and ninety-nine. For example:
Use a hyphen to separate the numerator from the denominator in a fraction. For example:
Use a hyphen to avoid confusion and misreading including awkward letter combinations. For example:
- un-ionized (not ionized instead of unionized)
- re-sign (sign again instead of resign)
- Spanish-speaking student (student who speaks Spanish, not a student from Spain who speaks)
- one-week vacation (vacation that is a week long, not a single week-long vacation)
Punctuation marks are a convention of written language that helps readers and writers more clearly understand writing by ensuring the clarity of writing. Hyphens perform seven basic functions in written American English: with affixes, in compound nouns, in coequal nouns, in compound modifiers, in phrasal modifiers, in numbers, and to avoid confusion and misreading.
Faigley, Lester. 2003. The Brief Penguin Handbook. New York: Pearson Longman.
Gibaldi, Joseph. 2003. MLA Handbook for Writers of Research Papers. 6th ed. New York: The Modern Language Association of America.