The hyphen's primary functions are to link words and sometimes numbers and to divide words at the ends of lines.
WITH COMPOUND WORDS
The hyphen joins compound words and compound numbers from twenty-one to ninety-nine and fractions when they are used as modifiers. When in doubt about whether or where to hyphenate a word, check your dictionary.
able-bodied, self-contained, brother-in-law twenty-one, one-sixteenth
WITH MODIFIERS
Two-word and three-word unit modifiers that express a single thought are hyphenated when they precede a noun (an out-of-date car, a clear-cut decision). Do not hyphenate cumulative adjectives (a new digital computer) or unit modifiers formed with an adverb ending in -ly (a rarely used computer, a badly needed vacation).
The presence or absence of a hyphen can alter the meaning of a sentence. Use a hyphen when it is needed for clarity
She was a magnetic card reader designer.
COULD MEAN
She was a magnetic-card reader designer.
OR
She was a magnetic card-reader designer.
When the modifying phrase follows the noun it modifies, it is not hyphenated.
Our office equipment is out of date.
A hyphen is always used in a unit modifier or a noun that begins with a letter or numeral.
five-cent candy, nine-inch gap, A-frame house [unit modifiers] H-bomb, T-square, 9-iron [nouns]
If a series of unit modifiers all end with the same term, it does not need to be repeated; for smoothness and brevity you may "suspend" the hyphens and use the modified term only at the end of the series.
change
The third-floor, fourth-floor, and fifth-floor rooms have recently been painted.
to
The third-, fourth-, and fifth-floor rooms have recently been painted.
WITH PREFIXES AND SUFFIXES
A hyphen is used after a prefix when the root word is a proper noun.
pre-Sputnik, anti-Stalmist, post-Newtonian
If there is a possibility of misreading, a hyphen can be used to separate the prefix and the root word, especially if the root begins with the letter that the prefix ends with. When in doubt, consult a dictionary.
re-elect, re-enter, anti-inflationary re-draw
In some cases, a hyphen is inserted after the prefix to change the meaning. Re-cover means "to cover anew," but recover means "to recuperate." Other words whose meaning can be changed with a hyphen include re-sent and resent, re-form and reform, and re-sign and resign. A hyphen is used when ex- means "former."
ex-partners, ex-wife
The suffix -elect is hyphenated.
president-elect, commissioner-elect
TO DIVIDE WORDS
Hyphens are used to divide words at the end of a line. Avoid dividing words whenever possible; but if you must divide them, use the following guidelines for hyphenation.
DIVIDE
• Between syllables (but leave at least three letters on each line)
let-ter
• Between the compound parts of compound words
time-table
• After a single-letter syllable in the middle of a word
sepa-rate
• After a prefix
pre-view
• Before a suffix
cap-tion
• Between two consecutive vowels with separate sounds
gladi-ator
DO NOT DIVIDE
• A word that is pronounced as one syllable
shipped
• A contraction
you're
• An abbreviation or acronym
AOPA
Divide a word spelled with a hyphen only after the hyphen. If the hyphen is essential to the word's meaning, do not divide the word.
OTHER USES OF THE HYPHEN
Hyphens should be used between letters showing how a word is spelled.
In his letter Dean misspelled believed b-e-l-e-i-v-e-d. Hyphens identify prefixes, suffixes, or written syllables.
Re-, -ism, and ex- are word parts that cause spelling problems.
A hyphen can stand tor to or through between letters and numbers. (However, when a number, letter, or date is preceded by the word from, the word to must be used instead of a hyphen.)
