Hyphen (-)

How to read it

The keyboard hyphen is Unicode’s U+002D HYPHEN-MINUS, a character the standard calls ambiguous: it is “used generically for hyphen, minus sign or en dash”. CMOS Shop Talk, from the Chicago Manual of Style, explains the name: before Unicode was published in 1991, the same character did duty as the minus sign. Unicode also encodes a hyphen proper, U+2010 HYPHEN, for words such as “left-to-right”, and prefers it in typeset text, but Chicago points out that it is not what the hyphen key types and so is not what most documents contain. The American Heritage Dictionary defines the hyphen as the mark between the parts of a compound word or name, or between the syllables of a word, especially one divided at the end of a line. Chicago notes that it is the only one of the dashes with its own key on a standard keyboard.

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Hyphen, en dash, em dash or minus sign?

CMOS Shop Talk puts the difference in one line: “hyphens connect groups of words or numbers whereas dashes set things off.” A range of numbers, such as 3–5, takes an en dash in Chicago style, and a break in a sentence takes an em dash. Because the hyphen is the mark on the keyboard, people often type it in place of a dash, with a space either side or doubled, and Chicago says replacing these is one of the first things many copyeditors do; Microsoft Word turns a double hyphen into an em dash by default. The minus sign looks like an en dash, but Chicago notes that it is designed to line up with the horizontal stroke of a plus sign.

How style guides use it

Matthew Butterick’s Practical Typography lists three uses: the hyphen a word processor adds when a word breaks at the end of a line, words spelled with a hyphen (topsy-turvy, cost-effective), and phrasal adjectives, where it settles the meaning. His example is “five dollar bills”: with no hyphen it reads as five bills of a dollar each, and “five-dollar bills” are bills worth five dollars. Butterick and the Guardian’s style guide both leave out the hyphen after an adverb ending in -ly (a closely held company, a hotly disputed penalty). The Guardian otherwise prefers one word wherever possible, saying hyphens “tend to clutter up text”, but uses them in short compound adjectives (two-tonne vessel, 19th-century artist) and wherever leaving one out would be ambiguous: “black-cab drivers come under attack” is not the same as “black cab-drivers come under attack”.

Spellings drift. The Guardian quotes the grammarian Rodney Huddleston on compounds moving from space to hyphen to a single word, and notes that “wire-less” and “down-stairs” were once hyphenated. Cambridge Dictionary says hyphens are becoming less common, so that post-box is also written post box and postbox. GOV.UK, the UK government’s style guide, hyphenates co-operate, co-ordinate and re- before an e (re-evaluate), but not reuse or email, and otherwise uses a hyphen only where a phrase is confusing without one: “a little used-car is different from a little-used car”.

Other jobs it does

The US Government Publishing Office’s Style Manual uses hyphens between the letters of a word spelled out (H-a-l-i-g-o-n-i-a-n), to separate the elements of a chemical formula, and to stand for deleted letters or illegible words. Chicago uses them between the groups of digits in phone numbers and ISBNs (978-0-226-81797-2). The Oxford Advanced Learner’s Dictionary adds the hanging hyphen that shows something is missing, as in short- and long-term.

The soft hyphen

Unicode’s U+00AD SOFT HYPHEN is, in the standard’s words, “not a hyphen, but rather an invisible format character used to indicate optional intraword breaks”.