hyphens, general rules (APA 6th, 4.13; CMS 15th, 6.1)
Like those for using commas, the general rules for using hyphens are not always dependable. Exceptions abound. Some common cases are listed as individual entries in this style manual, and the following general rules should provide some guidance, but it is impossible to cover all cases in a work of this size. Therefore, in deciding whether a given compound should be open (two words, no hyphen), closed (one word, no hyphen), or hyphenated, IRA authors and editors are advised to consult the dictionary, APA 6th, 4.13, and CMS 15th, 6.1. For lengthy projects, noting temporary compounds and their treatment on a written style sheet will help maintain consistency and reduce the amount of “looking up” we have to do.
- Use hyphens to clarify how words and phrases relate to one another (i.e., which should be understood as a unit, and which should not).
Example: I am looking for twenty four year old bottles of wine.
How many bottles? How old? Placing the hyphen(s) correctly can eliminate the ambiguity of the original phrase. (20 four-year-old bottles or 24 year-old bottles)
- Use hyphens in certain standard compounds.
Examples: mother-in-law; great-grandchild; over-the-counter. The dictionary will normally list these compounds, with hyphens, as main entries.
- Use hyphens to indicate certain temporary compounds, especially adjective phrases that appear before the nouns they modify (sometimes called unit modifiers). Those that follow the noun are usually open. The following forms are among the most common:
Note: When alternative compound adjectives are used, the word standing alone is followed by a hyphen and a space: hard- and soft-boiled eggs; high- and low-frequency words; 2- and 3-year-old children
- Adjective phrases containing participles: an all-knowing teacher; a thought-provoking article; a never-ending process; a hard-won victory; teacher-directed activities; a meaning-centered approach
(but The victory was hard won. The approach is meaning centered.)
- Noun–adjective compounds: labor-intensive activities; gender-neutral terminology
(but The activities were labor intensive. The terminology is gender neutral.)
- Adjective–noun compounds: low-frequency words; 14th-century structures
(but The structures were built in the 14th century); long-vowel sounds; short-vowel sounds
- Adjective phrases that include a whole number or fraction: two-way street; 12th-grade student; 4-year-old child; half-eaten biscuit
(but The student is in 12th grade. The child is 4 years old.)
- Noun-noun compounds used as adjectives: data-analysis methods (but We used several methods of data analysis.)
- Some common adjective phrases should not be hyphenated:
- Compounds that include an adverb ending in ly: newly discovered elements; recently published articles; widely used texts
- Compounds including comparative or superlative adjectives: higher achieving students; least efficient methods; most recent discoveries. (Note IRA exceptions for better, best.)
- Compounds whose second element is a number or letter: Title I programs; Group B participants; Type A behavior (Note that first word in these compounds is almost always capitalized; grade 1 is an exception.)
- Use a hyphen to indicate a word break at the end of a line of type. (see word division)