Hyphen Clinic

Language is living. It changes. We see this especially with the use of hyphens. Two words are first joined together with a hyphen, and then after many years the hyphen disappears, and one, new word is left.

For example, did you know that "today" and "tomorrow" used to be spelled "to-day" and "to-morrow"? The trend in research writing is not to use hyphens when you don't need to.

Use a hyphen when you use two or more words BEFORE a noun that ACT AS ONE IDEA: a six-month period, woman-centered care, high-risk pregnancy, patient-awareness survey, high-impact surgery, low-calorie diet, AIDS-related complications, etc.

Note: Some expressions are always linked by a hyphen, no matter where they come: full-time, HIV-positive, over-the-counter.

Do NOT use a hyphen after an adverb ending with -ly: a carefully planned project, a recently discovered virus

Use hyphens to write numbers twenty-one to ninety-nine and fractions (five-eighths, one-fourth)

The prefixes self-, all-, ex-, and cross- almost always require a hyphen (self-reported, all-inclusive, ex-husband, cross-cultural)

Use a hyphen when the prefix ends with the same letter that begins the word: anti-inflammatory, de-emphasize. But not always! Unnatural, coordinate, cooperate, etc.

Do NOT hyphenate words prefixed by semi, non, un, in, dis, co, anti, hyper, pre, re, post, out, bi, counter, de, mis, mega, micro, inter, over, and under (among others).
semistructured, nonemergency, uninfected, inpatient, disorder, coworker, antismoking, antibacteria, hypertension, preoperative, reoccur, postoperative, posttraumatic, outpatient, bimonthly, countermeasure, decompress, misdiagnosed, megabyte, microscopic, interconnected, interdisciplinary, overemphasize, override, underrepresented, underestimate

If you don't know whether to use a hyphen or not, DON'T WORRY! Most native English writers make hyphen mistakes, too. ドンマイ！ドンマイ！