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Hyphens are used to form select compound words and to break words at the end of a line.

M1-a Use a hyphen to join compound adjectives that precede nouns.

When a compound adjective precedes a noun, the hyphen clarifies that the compound functions as a unit.

When two different prefixes or initial words go with the same second word, use a hyphen and a space at the end of the first prefix or word.

Note: Some compound adjectives are nearly always hyphenated, before or after a noun, including those beginning with all- or self-. Check a dictionary if you are not sure whether a hyphen is needed.

A compound with an -ly adverb preceding an adjective or a participle is always left as two words.

M1-b Present a compound noun as one word, as separate words, or as a hyphenated compound.

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Close up the parts of a compound noun spelled as one word.

Omit hyphens in a compound noun spelled as separate words.

Hyphenate fractions, compound numbers (up to ninety-nine), and other nouns that are hyphenated in your dictionary.

Note: If using compound words that have more than one acceptable spelling (workforce and work force, for example), choose one spelling and use it consistently. If you are unsure about whether to use a hyphen, check your dictionary, or follow the common usage of professional publications in that field.

M1-c Spell words formed with most prefixes as one word with no hyphen.

Insert a hyphen in a compound noun beginning with ex-, great-, or self- (unless it is followed by a suffix, as in selfhood) or ending in -elect or -in-law.

Use a hyphen in a word that includes a prefix and a proper noun.

M1-d Use a hyphen when necessary to avoid ambiguity.

Sometimes a hyphen is necessary to prevent a reader from confusing a word with a prefix (re-cover, re-creation) with another word (recover, recreation) or from stumbling over a word in which two or three of the same letters fall together (anti-inflammatory, troll-like).

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M1-e Insert a hyphen between syllables to divide a word at the end of a line.

If you must divide a word, look for a logical division, such as between syllables, between parts of a compound word, or between the root and a prefix or suffix. If you are uncertain about where to divide a word, check your dictionary.

Although many published works divide words, writing is easier to read without numerous broken words.