A hyphen (- ) is a punctuation mark. It is used for both: words to join and to separate syllables. It is often confused with the dashes (–, —, ― ), which are longer and have different functions, and with the minus sign (− ) which is also longer. The use of hyphens is called hyphenation.
Hyphens are most commonly used to break single words into parts, or to join ordinarily separate words into single words.
A definitive collection of hyphenation rules does not exist. Therefore, the writer or editor should consult a manual of style or dictionary of his or her preference, preferably for the country in which he or she is writing. The rules of style that apply to dashes and hyphens have evolved to support ease of reading in complex constructions; editors often accept deviations from them that will support, rather than hinder, ease of reading. Spaces should not be placed between a hyphen and either of the words it connects except when using a suspended hyphen (e.g. nineteenth- and twentieth-century writers—see below).
The use of the hyphen in compound nouns and verbs has, in general, been steadily declining. Compounds that might once have been hyphenated are increasingly left with spaces or are combined into one word. The sixth edition of the Shorter Oxford English Dictionary removed the hyphens from 16,000 entries, such as fig-leaf (now fig leaf), pot-belly (now pot belly) and pigeon-hole (now pigeonhole). In other countries hyphens are dropped in favor of connecting the two-word compounds. Use of the hyphen is particularly avoided by those concerned with visual cleanliness, for example writers of advertising copy, packaging labels etc.
However, a significant number of compounds are still routinely hyphenated (e.g. breast-feed, add-on (noun), get-together, merry-go-round). Hyphenation remains the norm in certain compound modifier constructions and, amongst some authors, with certain prefixes (see below). Hyphenation is also routinely used to avoid unsightly spacing in justified texts (for example, in newspaper columns).
To allow more efficient usage of paper, more regular appearance of right-side margins without requiring spacing adjustments, and to eliminate the need to erase hand-written long words begun near the end of a line that do not fit, words may be divided at the nearest breakpoint between syllables and a hyphen inserted to indicate that the letters form a word fragment, not a word. For example:
|Without hyphenation||With hyphenation|
We, therefore, the|
representatives of the United
States of America...
We, therefore, the represen-|
tatives of the United States
The details of doing this properly are complex and language-dependent and can interact with other orthographic and typesetting practices: see justification and hyphenation algorithm. Such hyphenation algorithms, when employed in concert with dictionaries, are sufficient for all but the most formal texts.
In general, prefixes and suffixes are affixed to another word. Certain prefixes (co-, pre-, mid-, de-, non-, anti-, etc.) are often improperly hyphenated, though usage varies between American and British English. British English tends towards hyphenation (pre-school) whereas American English tends towards omission of the hyphen (preschool). A hyphen is mandatory when a prefix is applied to a proper (capitalized) adjective (un-American, de-Stalinisation).
In British English, hyphens may be employed where readers would otherwise be tempted into a mispronunciation (e.g. co-worker is so punctuated partly to prevent the reader's eye being caught automatically by the word cow). The AP Stylebook provides further information on the use of "co-" as a prefix.
Hyphens may be used, in association with prefixes, suffixes or otherwise, when repeated vowels or consonants are pronounced separately rather than being silent or merged in a diphthong. For example: shell-like, anti-intellectual. In the vowel-vowel case, some English authorities use a diaeresis (as in coöperation, rather than co-operation or cooperation), but this style is now rare.
Some prefixed words are hyphenated to distinguish them from other words that would otherwise be homographs, such as recreation (fun or sport) and re‑creation (the act of creating again), or predate (what a predator does) and pre‑date (to be of an earlier calendar date).
Hyphens are occasionally used to denote syllabification, as in syl-lab-i-fi-ca-tion. Most American dictionaries use an interpunct, sometimes called a "middle dot" or "hyphenation point", for this purpose, as in syl·lab·i·fi·ca·tion. Similarly, hyphens may be used to imply the spelling of a word, such as "W-O-R-D spells word".
Compound modifiers are groups of two or more words that jointly modify the meaning of another word. When a compound modifier, other than a noun–noun or adverb–adjective combination, appears before a term, the compound modifier is generally hyphenated to prevent any possible misunderstanding, such as in American-football player or real-world example. Without the hyphen, there is potential confusion about whether American applies to football or player, or whether the author might perhaps be referring to a "world example" that is "real". Compound modifiers can extend to three or more words, as in ice-cream-flavored candy, and can be adverbial as well as adjectival (spine-tinglingly frightening).
When the same combination of words follows the term it applies to, hyphens may or may not be required, depending on whether the compound constitutes an adjective or not. For example: American-football player / a player of American football and real-world example / an example from the real world, since the compounds are not adjectives. Instead, time-sensitive documents / the documents are time-sensitive and left-handed catch / he took the catch left-handed, as the compounds are adjectives.
Hyphens are not normally used in noun–noun compound modifiers, when no confusion is possible; for example: government standards organization and department store manager.
Hyphens should not normally be used in adverb–adjective modifiers such as wholly owned subsidiary and quickly moving vehicle (because the adverbs clearly modify the adjectives; "quickly" does not apply to "vehicle" as "quickly vehicle" would be meaningless). However, if the adverb can also function as an adjective, then a hyphen may be required for clarity. For example, the phrase more-important reasons ("reasons that are more important") is distinguished from more important reasons ("additional important reasons"), where more is an adjective. A mass-noun example is the following: more-beautiful scenery as distinct from more beautiful scenery. Other examples are well-received speech and hard-won fight.
Hyphens are used to connect numbers and words in forming adjectival phrases (particularly with weights and measures), whether numerals or written out, as in 28-year-old woman (cf. twenty-eight-year-old woman) or 320-foot wingspan. The same usually holds for abbreviated time units. Hyphens are also used in spelled-out fractions as adjectives (but not as nouns), such as two-thirds majority and one-eighth portion. Note, though, that for use with symbols for SI units—as opposed to the names of those units—both the Bureau International des Poids et Mesures and the U.S. National Institute of Standards and Technology reject this practice, thus a roll of 35-millimeter film, but not a 25-kg sphere.
Where an adjective–noun compound would be plural standing alone, it usually becomes singular and hyphenated when modifying another noun. For example, four days becomes four-day week.
An en dash (– ) sometimes replaces the hyphen in hyphenated compounds if either of its constituent parts is already hyphenated or contains a space (e.g. high-priority–high-pressure tasks (tasks which are both high-priority and high-pressure). En dashes are more proper than hyphens in ranges (pp. 312–14), relationships (blood–brain barrier) and to convey the sense of to (Boston–Washington race).
Connecting hyphens are used in a large number of miscellaneous compounds, other than modifiers, such as in lily-of-the-valley, cock-a-hoop, clever-clever, tittle-tattle and orang-utan. Usage is often dictated by convention rather than fixed rules, and hyphenation styles may vary between authors; for example, orang-utan is also written as orangutan or orang utan, and lily-of-the-valley may or may not be hyphenated.
Two-word names of numbers less than one hundred are hyphenated. For instance, the number 23 should be written twenty-three, and 123 should be written one hundred and twenty-three. (The and is omitted in American English.)
Some married couples compose a new surname (sometimes referred to as a double-barrelled name) for their new family by combining their two surnames with a hyphen. Jane Doe and John Smith might become Jane and John Smith-Doe, or Doe-Smith, for instance. In some countries, however, only the woman hyphenates her birth surname, appending her husband's surname.
A suspended hyphen (also referred to as a "hanging hyphen" or "dangling hyphen") may be used when a single base word is used with separate, consecutive, hyphenated words which are connected by "and", "or", or "to". For example, nineteenth-century and twentieth-century may be written as nineteenth- and twentieth-century. This usage is derived from that of German, which uses a dangling hyphen when the second word is unhyphenated, e.g., Die Lumpen- und Arbeiterproletariaten.
A hyphen may be used to connect groups of numbers, such as in dates (see below), telephone numbers or sports scores.
The hyphen is sometimes used to hide letters in words, as in G-d, although an en-dash can be used as well for stylistic purposes (“G–d”).
Some strong examples of semantic changes caused by the placement of hyphens:
Additional examples of proper use:
Note, though, that many authoritative sources, such as the Chicago Manual of Style, recommend writing commonplace compounds open (i.e., without hyphen) when they appear after the noun they modify and when they are used adverbially. Thus
Similarly, for the adverbial use compare
The likely first use of the hyphen—and its origination—ought to be credited to Johannes Gutenberg of Mainz, Germany circa 1455 with the publication of his 42-line Bible. Examination of an original copy on vellum (Hubay index #35) in the U. S. Library of Congress shows that Gutenberg's movable type was set justified in a uniform style, 42 equal lines per page.
Prior to Gutenberg setting the first lines printed in the Western world with movable type, there was no need for hyphens or the justification of lines to equal length. The Gutenberg printing press required words made up of individual letters of type to be held in place by a surrounding non-printing rigid frame. Gutenberg solved the problem of making each line the same length to fit the frame by inserting a hyphen as the last element at the right side margin. This interrupted the letters in the last word, requiring the remaining letters be carried over to the start of the line below. His hyphen appears throughout the Bible as a short, double line inclined to the right at a 60-degree angle.
In medieval times and the early days of printing, the predecessor of the comma was a slash. As the hyphen ought not to be confused with this, a double-slash was used, this resembling an equals sign tilted like a slash. Writing forms changed with time, and included the full development of the comma, so the hyphen could become one horizontal stroke.
However, publishers of dictionaries liked that a tilted symbol would give them a little extra room in their books. Those dictionaries based on the second edition of the Merriam-Webster dictionary used one small, slightly tilted slash for a hyphen which they added at the end of a line where they broke the word, but used a double-slash, much like the very old symbol, to indicate a hyphen that was actually a part of the phrase but just happened to fall at the end of the line. This double-slash would be used in hyphenated phrases in the middle of the text as well, so that there would be no confusion.
In the ASCII character encoding, the hyphen was encoded as character 45. Technically, this character is called the hyphen-minus, as it is also used as the minus sign and for dashes. In Unicode, this same character is encoded as ( - ) so that Unicode remains compatible with ASCII. However, Unicode also encodes the hyphen and minus separately, as U+2010 ( ‐ ) and U+2212 ( − ), respectively, along with a series of dashes. Use of the hyphen-minus character is discouraged where possible, in favour of the specific hyphen character. Nevertheless, since the Unicode hyphen is awkward to enter on normal keyboards, the hyphen-minus character remains extremely common. Hyphens are often used instead of dashes in situations where proper dash characters are unavailable (such as ASCII-only text) or difficult to enter, or when the writer is unaware of the difference. Some writers use two hyphens (--) to represent a dash in ASCII text.
When flowing text, it is sometimes preferable to break a word in half so that it continues on another line rather than moving the entire word to the next line. Since it is difficult for a computer program to automatically make good decisions on when to hyphenate a word the concept of a soft hyphen was introduced to allow manual specification of a place where a hyphenated break was allowed without forcing a line break in an inconvenient place if the text was later reflowed. In contrast, a hyphen that is always displayed and printed is called a hard hyphen (though some use this term to refer to a non-breaking hyphen; see below). Soft hyphens are most useful when the width is known but future editability is desired. In contrast, in a medium such as the World Wide Web, where the author has little control over the width of the displayed text, manually marking all possible hyphenation points would be extremely tedious. (In the case of the Web, CSS version 3 will provide a solution in the form of language-specific hyphenation dictionaries.)
When flowing text, a system may consider the soft hyphen to be a point at which a word may be broken, and display a hyphen at the end of the broken line; if the line is not broken at that point the hyphen is not displayed. In most parts of ISO-8859 the soft hyphen is at position 0xAD, and since the first 256 positions in Unicode are taken from ISO-8859-1, it has a Unicode codepoint of U+00AD. In HTML, the soft hyphen is encoded as the character entity '
Most text systems consider a hyphen to be a word boundary and a valid point at which to break a line when flowing text. However, this is not always desirable behavior, especially when it could lead to ambiguity (such as in the examples given before, where recreation and re‑creation would be indistinguishable). For this purpose, Unicode also encodes a non-breaking hyphen as U+2011 ( ‑ ). This character looks identical to the regular hyphen, but is not treated as a word boundary.
The ASCII hyphen-minus character is also often used when specifying parameters to programs in a command line interface. The character is usually followed by one or more letters that indicate specific actions. Typically it is called a dash in this context. This is used in many different operating systems, particularly Unix and Unix-like systems. DOS and Microsoft Windows also sometimes make use of the hyphen, although the use of a forward slash (/) is more prevalent there. A parameter by itself that is only a single hyphen without any letters usually means that a program is supposed to handle data coming from the standard input or send data to the standard output. Two hyphen-minus characters ( -- ) are used on some programs to specify "long options" where more descriptive action names are used. This is a common feature of GNU software.
Continental Europeans use the hyphen to delineate parts within a written date. Germans and Slavs also used Roman numerals for the month; 14‑VII‑1789, for example, is one way of writing the first Bastille Day, though this usage is rapidly falling out of favour. Plaques on the wall of the Moscow Kremlin are written this way. Usage of hyphens, as opposed to the slashes used in the English language, is specified for international standards.
International standard ISO 8601, which was accepted as European Standard EN 28601 and incorporated into various typographic style guides (e.g., DIN 5008 in Germany), brought about a new standard using the hyphen. Now all official European governmental documents use this. These norms prescribe writing dates using hyphens: 1789-07-14 is the new way of writing the first Bastille Day.
This method has gained influence within North America, as most common computer filesystems make the use of slashes difficult or impossible. Windows uses both and / as the directory separator, and / is also used to introduce and separate switches to shell commands. Unix-like systems use / as a directory separator and, while is legal in filenames, it is awkward to use as the shell uses it as an escape character. Unix also uses a space followed by a hyphen to introduce switches. The non-year form is also identical apart from the separator used to the standard American representation.
The ISO date format sorts correctly using a default collation, which can be useful in many computing situations including for filenames, so many computer systems and IT technicians have switched to this method. The government of the Commonwealth of Massachusetts, for example, has switched to this method.