Just as all punctuation marks ensure the clarity of writing, hyphens function to avoid confusion and misreading by joining compound words including nouns and other modifiers. Hyphens perform seven basic functions.
Compound numbers and fractions
1. Use hyphens with compound numbers between and including twenty-one and ninety-nine. For example:
Also use hyphens to separate numerators and denominators in fractions. For example:
2. Use hyphens with some compound nouns. For example:
Do not use hyphens with other compound nouns. For example:
The best way to determine if a compound noun requires a hyphen is to consult a dictionary.
3. Use hyphens to join coequal nouns. For example:
Do not use hyphens between nouns in which the first noun modifies or describes the second. For example:
- child actor
- football player
- chocolate cake
4. Use hyphens to join compound modifiers that precede nouns. For example:
- middle-class family
- self-fulfilling prophecy
- soft-hearted neighbor
Use hyphens to join adjectives with adverbs such as better, best, ill, lower, little, and well. For example:
- well-known novelist
- better-prepared student
- ill-mannered child
Use hyphens to join compound modifiers in which the second word is the present or past participle of a verb. For example:
- sports-loving uncle
- fear-inspired devotion
- hate-filled rhetoric
Use hyphens to join compound modifiers that contain numbers. For example:
- sixth-floor stacks
- second-semester freshmen
- twentieth-century literature
Do not use hyphens to join compound modifiers that follow state-of-being verbs and that directly modify the subject of the sentence. For example:
- The author is well known.
- Those peanuts are chocolate covered.
- This child is ill mannered.
- My students were better prepared.
Do not use hyphens to join adjectives with adverbs ending in -ly or the adverbs too, very, or much. For example:
- very hungry caterpillar
- too ripe tomatoes
- much loved grandmother
- extremely terrible day
Phrases as modifiers
5. Use hyphens to separate words in phrases functioning as modifiers that precede nouns. For example:
- all-you-can-eat buffet
- out-of-this-world experience
- over-the-counter medication
Prefixes and suffixes
6. Use hyphens with certain prefixes and suffixes such as all-, anti-, -elect, ex-, mid-, neo-, post-, pre-, pro-, and self-. For example:
Use hyphens with the prefixes anti-, mid-, neo-, post-, pre-, and pro- that precede proper nouns and numbers. For example:
- post-Vietnam War
Do not use hyphens with most other prefixes. For example:
Avoid confusion and misreading
7. Use hyphens to avoid confusion and misreading. Use hyphens to avoid awkward letter combinations. For example:
- re-sign (as in to sign again, not resign or quit)
- English-language student (a student studying English, not an English speaking student studying language)
- semi-independent (not *semiindependent)
The accompanying printable reference sheet of the rules for using colons in English is available for download at The Use of Hyphens in Written English Reference Sheet.