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The hyphen (‐) is a punctuation mark used to join words and to separate syllables of a single word. The use of hyphens is called hyphenation. The hyphen should not be confused with dashes (‒, –, —, ―), which are longer and have different uses, or with the minus sign (−), which is also longer.
In terms of an orthographic concept, the hyphen is a single entity. In terms of character encoding and display, that entity is represented by any of several characters and glyphs (including hard hyphens, soft or optional hyphens, and nonbreaking hyphens), depending on the context of use (discussed below).
Although, as mentioned above, hyphens are not to be confused with en dashes and minus signs, there are some overlaps in usage (in which either a hyphen or an en dash may be acceptable, depending on user preference; discussed below) and in character encoding (which often uses the same character, called a "hyphen-minus", to represent both the hyphen and minus sign entities; discussed below).
The term (ἡ) ὑφέν ((he) hyphén), was used for a caret-like (^) sign written below two consecutive letters to indicate that they belong to the same word (when it was necessary to avoid ambiguity before the space was in regular use).
Hyphens are mostly used to break single words into parts, or to join ordinarily separate words into single words. Spaces should not be placed between a hyphen and either of the words it connects except when using a suspended or "hanging" hyphen (e.g. nineteenth- and twentieth-century writers).
A definitive collection of hyphenation rules does not exist; rather, different manuals of style prescribe different usage guidelines. 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.
The use of the hyphen in English 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. In 2007, 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). The advent of the Internet and the increasing prevalence of computer technology have given rise to a subset of common nouns that might have been hyphenated in the past (e.g. "toolbar", "hyperlink", "pastebin").
Despite decreased use, hyphenation remains the norm in certain compound-modifier constructions and, amongst some authors, with certain prefixes (see below). Hyphenation is also routinely used as part of syllabification in justified texts to avoid unsightly spacing (especially in columns with narrow measure, such as in newspapers).
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. The word may be divided at the nearest break point between syllables (syllabification), and a hyphen inserted to indicate that the letters form a word fragment, rather than a full word. This allows more efficient use of paper, allows flush appearance of right-side margins (justification) without oddly large word spaces, and decreases the problem of rivers. This kind of hyphenation is most useful when the width of the column (called the measure in typography) is very narrow. For example:
We, therefore, the
We, therefore, the represen-
The details of doing this properly are complex and language-dependent and can interact with other orthographic and typesetting practices. Hyphenation algorithms, when employed in concert with dictionaries, are sufficient for all but the most formal texts. See also justification.
Prefixes (such as de-, pre-, re-, and non-) and suffixes (such as -less, -like, -ness, and -hood) may or may not be hyphenated. (The unhyphenated style is also called closed up or solid.) A rule of thumb is that they are not hyphenated unless the lack of a hyphen hurts clarity—specifically, clarity at first glance rather than clarity upon a second look or a moment's pause. The clear/unclear distinction involves some subjectivity, because what is instantly clear to one reader may not be to another (depending on, for example, subject matter familiarity). Nonetheless, consensus among users of a language often reduces that subjectivity for many words. This is explained further below.
Many long-established words, such as disgusted, degrade, and refresh, do not require a hyphen because they are fully fused to the point that their first syllable is barely even thought about as having a prefix function (even though in many such words, if one stops to think about it, one can clearly see it). Many other words, such as prewashed or repainted, may not be quite so fully fused (the prefix function may be slightly more prominent in consciousness), but nonetheless they require no hyphen, because (1) most readers recognize the closed-up word as a familiar one and thus have no trouble parsing the syllables, and (2) if all such words were hyphenated, the many hyphens throughout the text would seem superfluous.
In contrast, for some other words, the closed-up style may not be as clear, and the hyphen can ensure clarity and avoid awkwardness, including "odd appearance" or misguided parsing of syllables. An example of avoiding misguided parsing would be to hyphenate the word co-worker (versus coworker) to prevent the reader's eye being caught automatically by the letter group cow (which might suggest cow (//) before backtracking and reparsing occurred). In such cases, styling varies depending on individual preference, regional preference, occupational specialty, or style guide preference, because the definition of "awkwardness" for any given word depends on who is judging it.
Words for which prefix hyphenation is least subjective, to the point that closed-up style is widely rejected, are of several classes. One such class consists of a few words that require a hyphen to distinguish them from other words that would otherwise be homographs, such as recreation (fun or sport) versus re-creation (the act of creating again), retreat (turn back) versus re-treat (give therapy again), and un-ionized (not in ion form) versus unionized (organized into trade unions). The other classes are those in which the prefix is applied to (1) a proper (capitalized) noun or adjective (un-American, de-Stalinisation); (2) an acronym (anti-TNF antibody, non-SI units); or (3) a number (pre-1949 diplomacy, pre-1492 cartography).
Style guides codify rules to minimize inconsistency, the ultimate goal of which is to have the style unnoticed by the reader (that is, to avoid catching the reader's eye, either with trivial differences or with a lot of superfluous hyphens). The style guide rules allow exceptions to avoid awkwardness. For example, a guide will typically say to follow dictionary X's style for any word entered therein, and for words not entered, to close up by default and thus hyphenate only to avoid awkwardness. Such a rule successfully codifies almost all choices and thus leaves little to discretion except a few rare or neologistic words, which are safely hyphenated. This ensures high intradocument and interdocument consistency. Rules about avoiding doubled vowels or doubled consonants are often mentioned in style guides. These appropriately cascade only downstream, not upstream, of the "follow dictionary X" rule, because most dictionaries close up many well-established doubled-letter pairs. (For example, any style that follows Merriam-Webster's Collegiate Dictionary thus closes up preempt, reexamine, deemphasize, nonnegotiable, posttransfusion, and hundreds of others.) As mentioned earlier, the definition of "awkwardness" for any given word is inherently subjective but nonetheless also subject to consensus. For example, reexamine and deemphasize are accepted as nonawkward by a broad consensus; to prefer the hyphenated styling is a matter of opinion, but to insist that the solid styling is awkward would be considered pedantic by many educated readers. However, some doublings attract smaller majorities than others in such a consensus; with the co-worker/coworker example (mentioned earlier) or with antiinflammatory/anti-inflammatory, many readers may consider solid styling nonawkward whereas plenty of others don't, and in such cases, dictionary styles may vary (Dorland's, antiinflammatory; Merriam-Webster's Medical Dictionary, anti-inflammatory). Tripled letters rarely occur, but when they do, the hyphen is considered mandatory (thus shell-like, not shelllike).
There is a trend that over decades, words that once were hyphenated for clarity lose the hyphen as their familiarity grows. An excellent example is email/e-mail; the number of people who find email awkward dropped from the 1990s to the 2010s, and thus the hyphen has been dropped increasingly. For some instances, the consensus depends on occupational specialty or subspecialty. Although proto-oncogene is still hyphenated by most users (and by both Dorland's and Merriam-Webster's Medical), the solid styling (protooncogene) is gaining popularity, with oncologists and geneticists (for whom the term is most familiar) leading the way.
A hyphen can clarify that two adjacent vowels—whether two of the same letter (e.g., oo, ee) or two different letters (e.g., ae, ei)—are pronounced separately rather than being merged in a diphthong. The question is how necessary the clarification is. Thus, hyphenated de-escalate and co-operation have plenty of support, consensus-wise (plenty of users consider their hyphens as not superfluous), although solid deescalate and cooperation have plenty of support as well (plenty of users consider the hyphens superfluous). Consensus for styling varies by class, subclass, and even by individual word, with the common theme being that internal punctuation drops out of any combination judged as instantly recognizable enough in its context not to need it. As classes, there are doubling (namely, aa, ee, ii, oo, uu, yy) and nondoubling (for example, a+e, a+i, a+o; e+e, e+i, e+o). Several subclasses exist. There are combinations that are not rare in English as diphthongs and also not rare as nondiphthongs for users willing to style prefixed words solidly (such as ee and ei); regarding de+e/re+e/pre+e and de+i/re+i/pre+i, nearly everyone agrees that some fully fused examples (such as reiterate and reinforce) need no hyphen, but other examples have more evenly split pluralities (such as reexamine/re-examine or deemphasize/de-emphasize). There are combinations that are rare in English as diphthongs (for example, aa and ii) but not rare in prefixed words for those willing to style them solidly; and thus either they hardly need clarification within prefixed words (the solidification argument; thus intraarterial and antiinflammatory) or they need a hyphen to avoid looking like rare diphthongs, which are "odd-looking" because rare (the hyphenation argument, thus intra-arterial and anti-inflammatory).
A diaeresis can also sometimes be used, either to indicate nondiphthong status (as in coöperation and naïve) or to indicate nonsilent terminal -e (as in Brontë), but there are several implicit boundaries on this style's use; it is now rare (its peak of popularity was in the late 19th and early 20th centuries), and it was never applied extensively across the language (only a handful of examples, including coöperation, naïve, and Brontë, are encountered with any appreciable frequency in English; for whatever reason, it never had any popularity in the de+e/re+e/pre+e or de+i/re+i/pre+i subclasses—thus never *reëxamine, *reïterate, *deëmphasize, or others, although they might have been useful). Many users (and various dictionaries) consider the diaeresis optional in naive/naïve (because not necessary for the reader to recognize the word), and *na-ive draws attention to itself as a style that is simply never used (although comprehensible). For deity and deify, only solid styling (no hyphen or diaeresis) is normative.
Hyphens are occasionally used to denote syllabification, as in syl-la-bi-fi-ca-tion. Most British and North American dictionaries use an interpunct, sometimes called a "middle dot" or "hyphenation point", for this purpose, as in syl·la·bi·fi·ca·tion. This allows the hyphen to be reserved only for places where a hard hyphen is intended (for example, self-con·scious, un·self·con·scious, long-stand·ing). Similarly, hyphens may be used to indicate a word is being or should be spelled. For example, 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 an adverb–adjective combination appears before a term, the compound modifier is often hyphenated to prevent misunderstanding, such as in American-football player or little-celebrated paintings. Without the hyphen, there is potential confusion about whether the writer means a "player of American football" or an "American player of football" and whether the writer means paintings that are "little celebrated" or "celebrated paintings" that are little. 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). However, if the compound is a familiar one, it is usually unhyphenated. For example, at least one style guide prefers the construction high school students, to high-school students. Although the expression is technically ambiguous ("students of a high school"/"school students who are high"), it would normally be formulated differently if other than the first meaning were intended. Noun–noun compound modifiers may also be written without a hyphen when no confusion is likely: grade point average and department store manager. When the modifier is an adverb ending in -ly or when one of the parts is a proper noun or a proper adjective, there is no hyphen (e.g. "a badly written novel" or "a South American actor").
When a compound modifier follows the term to which it applies, a hyphen is typically not used if the compound is a temporary compound. For example, "that gentleman is well respected", not "that gentleman is well-respected"; or "a patient-centered approach was used" but "the approach was patient centered." But permanent compounds, found as headwords in dictionaries, are treated as invariable, so if they are hyphenated in the cited dictionary, the hyphenation will be used in both attributive and predicative positions. For example, "A cost-effective method was used" and "The method was cost-effective" (cost-effective is a permanent compound that is hyphenated as a headword in various dictionaries).
In the 19th century, it was common to hyphenate adverb–adjective modifiers with the adverb ending in -ly (in other words, producing the character string ly-). However, this has become rare. For example, wholly owned subsidiary and quickly moving vehicle are unambiguous, because the adverbs clearly modify the adjectives: "quickly" cannot modify "vehicle". However, if an adverb can also function as an adjective, then a hyphen may be or should be used for clarity, depending on the style guide. 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. Similarly, more-beautiful scenery (with a mass-noun) is distinct from more beautiful scenery. (In contrast, the hyphen in "a more-important reason/a more important reason" is not necessary, because the syntax cannot be misinterpreted.) A few words, including well and early, attract especial attention in this category. The hyphen in "well-[past_participled] noun", such as in "well-differentiated cells", might very reasonably be judged too superfluous to stet (the syntax cannot be misinterpreted), and yet plenty of style guides call for it. And because early has both adverbial and adjectival senses, its hyphenation can attract attention. Some editors, comparing with advanced-stage disease and adult-onset disease, like the parallelism of early-stage disease and early-onset disease. Similarly, the hyphen in little-celebrated paintings clarifies that one is not speaking of little paintings.
Hyphens are usually used to connect numbers and words in modifying phrases (such as in dimensional measurements of weight, size, and time) under the rationale that, like other compound modifiers, they take hyphens in attributive position (before the modified noun), although not in predicative position (after the modified noun). This is applied whether numerals or words are used for the numbers. Thus 28-year-old woman and twenty-eight-year-old woman or 32-foot wingspan and thirty-two-foot wingspan, but the woman is 28 years old and a wingspan of 32 feet. However, with symbols for SI units (such as m or kg)—as opposed to the names of these units (such as metre or kilogram)—both the International Bureau of Weights and Measures and the U.S. National Institute of Standards and Technology recommend use without a hyphen: a 25 kg sphere (which is why some scientists get annoyed when such hyphens are added to their article when it is edited for a journal using AMA style, whose hyphenation of these symbols bucks SI style). When the units are spelled out, this recommendation does not apply: a 25-kilogram sphere, a roll of 35-millimeter film.
In spelled-out fractions, hyphens are usually used when the fraction is used as an adjective but not when it is used as a noun: thus two-thirds majority and one-eighth portion but I drank two thirds of the bottle or I kept three quarters of it for myself. However, at least one major style guide hyphenates spelled-out fractions invariably (whether adjective or noun).
In English, an en dash ( – ) sometimes replaces the hyphen in hyphenated compounds if either of its constituent parts is already hyphenated or contains a space (for example, San Francisco–area residents, hormone receptor–positive cells, cell cycle–related factors, and public-school–private-school rivalries). A commonly used alternative style is the hyphenated string (hormone-receptor-positive cells, cell-cycle-related factors). (For other aspects of en dash–versus–hyphen usage, see Dash > En dash.)
When an object is compounded with a verbal noun, such as egg-beater (a tool that beats eggs), the result is sometimes hyphenated. Some authors do this consistently, others only for disambiguation; in this case, egg-beater, egg beater, and eggbeater are all common.
An example of an ambiguous phrase appears in they stood near a group of alien lovers, which without a hyphen implies that they stood near a group of lovers who were aliens; they stood near a group of alien-lovers clarifies that they stood near a group of people who loved aliens, as "alien" can be either an adjective or a noun. On the other hand, in the phrase a hungry pizza-lover, the hyphen will often be omitted (a hungry pizza lover), as "pizza" cannot be an adjective and the phrase is therefore unambiguous.
Similarly, there's a man-eating shark in these waters is nearly the opposite of there's a man eating shark at table 6; the first is a shark, and the second a man. A government-monitoring program is a program that monitors the government, whereas a government monitoring program is a government program that monitors something else.
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.
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 only the woman hyphenates her birth surname, appending her husband's surname.
A suspended hyphen (also called a "suspensive hyphen" or "hanging hyphen", or less commonly a "dangling" or "floating" 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 now common in English and specifically recommended in some style guides. Although less common, suspended hyphens are also used in English when the base word comes first, such as in "investor-owned and -operated". Usages such as "applied and sociolinguistics" (instead of "applied linguistics and sociolinguistics") are frowned on in English; the Indiana University Style Guide uses this example and says "Do not 'take a shortcut' when the first expression is ordinarily open." (i.e., ordinarily two separate words). This is different, however, from instances where prefixes that are normally closed up (styled solidly) are used suspensively. For example, preoperative and postoperative becomes pre- and postoperative (not pre- and post-operative) when suspended. Some editors prefer to avoid suspending such pairs, choosing instead to write out both words in full.
A hyphen may be used to connect groups of numbers, such as in dates (see below), telephone numbers or sports scores. It can also be used to indicate a range of values, although many styles prefer an en dash (see examples at Dash > En dash > Ranges of values).
The hyphen is sometimes used to hide letters in words (censoring), as in G-d, although an en dash can be used as well (“G–d”).
The hyphen is often used in reduplicatives.
Some strong examples of semantic changes caused by the placement of hyphens:
|This section does not cite any references or sources. (June 2006)|
The first use of the hyphen—and its origination—is often 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.
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.
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 is encoded as character 45. This character is actually called the hyphen-minus, and it is also used as the minus sign and for dashes. In Unicode, the hyphen-minus is encoded as U+002D (-) 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 the em dash U+2014 (—), en dash U+2013 (–) and other related characters. The hyphen-minus is a general-purpose character which attempts to fulfill several roles, and wherever optimal typography is desired, the preferred hyphen, minus, or other symbol should be used instead. For example, compare 4+3−2=5 (minus) and 4+3-2=5 (hyphen-minus); in most fonts the hyphen-minus will not have the optimal width, thickness, or vertical position, whereas the minus character will.
However, the Unicode hyphen is awkward to enter on most keyboards, so the hyphen-minus character remains very common. They are often used instead of dashes or minus signs in situations where the preferred characters are unavailable (such as ASCII-only text), where the preferred characters take effort to enter (via dialog boxes or multi-key, unmemorable keyboard shortcuts), or when the writer is unaware of the distinction. Some writers use two hyphen-minuses (--) to represent a dash in ASCII text.
The ASCII hyphen-minus character is also often used when specifying command-line options. The character is usually followed by one or more letters that indicate specific actions. Typically it is called a dash or switch in this context. Various implementations of the getopt() function to parse command-line options additionally allow the use of two hyphen-minus characters ( -- ) to specify long option names that are more descriptive than their single-letter equivalents. Another use of hyphens is that employed by programs written with pipelining in mind— a single hyphen may be recognized in lieu of a filename, with the hyphen then serving as an indicator that a standard stream, instead of a file, is to be worked with.
Although software (hyphenation algorithms) can often automatically make decisions on when to hyphenate a word at a line break, it is also sometimes useful for the user to be able to insert cues for those decisions (which are dynamic in the online medium, given that text can be reflowed). For this purpose, the concept of a soft hyphen (discretionary hyphen, optional hyphen) was introduced, allowing such manual specification of a place where a hyphenated break is allowed but not forced. That is, it does not force a line break in an inconvenient place when the text is later reflowed.
In contrast, a hyphen that is always displayed and printed is called a hard hyphen (although some use this term to refer to a non-breaking hyphen; see below). Soft hyphens are inserted into the text at the positions where hyphenation may occur. It can be a tedious task to insert the soft hyphens by hand, and tools using hyphenation algorithms are available that do this automatically. Current modules of the Cascading Style Sheets (CSS) standard provide language-specific hyphenation dictionaries.
The word segmentation rules of 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), or in languages other than English (e.g. a line break at the hyphen in Irish an t‑athair or Romanian s‑a would be undesirable). For this purpose, Unicode also encodes a nonbreaking hyphen (non-breaking hyphen, no-break hyphen) as U+2011 (‑, coded for by ‑). This character looks identical to the regular hyphen, but it is treated as a letter by word processors, namely that the hyphenated word will not be divided at the hyphen should this fall at what would be the end of a line of text; instead, the whole hyphenated word either will remain in full at the end of the line or will go in full to the beginning of the next line. The non-breaking space exists for similar reasons.
In parts of Europe, the hyphen is used 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. Use 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 is also the typical date format used in large parts of Eastern Europe and Asia, although sometimes with other separators than the hyphen.
This method has gained influence within North America, as most common computer filesystems make the use of slashes difficult or impossible. DOS, OS/2 and Windows simultaneously support both \ and / as directory separators, but / is also used to introduce and separate switches to shell commands (unless reconfigured to use the hyphen-minus in DOS). 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. Apart from the separator used the non-year form of the date format is also identical 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.
Apart from dash and minus sign, Unicode has multiple hyphen characters:
-) (still not to be confused with U+2212 − minus sign)
And in non-Latin scripts:
Unicode distinguishes the hyphen point from the general interpunct:
(See interpunct for more round characters.)
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