View source for Colon (punctuation)

{{Short description|Punctuation mark with two dots}}
{{About|the punctuation mark|a colon-like character used as an alphabetic letter in some languages, rather than as punctuation|Colon (letter)|other uses|Colon (disambiguation)}}
{{Use dmy dates|date=October 2025}}
{{Infobox symbol|mark={{not a typo|&colon;}}<!--Changing to regular colon breaks the infobox-->|name=Colon
|unicode={{unichar|003A|html=}}
|see also={{unichar|003B}}<br />Other types of colon, see list below.
|different from={{unichar|20A1}}
}}

The '''colon''', {{char|''':'''}}, is a [[punctuation]] mark consisting of two equally sized dots aligned vertically. A colon often precedes an explanation, a list,<ref name="PunctuationGuide">{{cite web |title=Colon |url=https://www.thepunctuationguide.com/colon.html |url-status=live |archive-url=https://web.archive.org/web/20201111194829/https://www.thepunctuationguide.com/colon.html |archive-date=11 November 2020 |access-date=22 November 2020 |website=The Punctuation Guide}}</ref> or a quoted sentence.<ref>{{cite book |url=https://ukshop.economist.com/products/the-economist-style-guide-12th-edition-e-book |title=The Economist Style Guide |section=punctuation |access-date=23 May 2021 |archive-url=https://web.archive.org/web/20210523100728/https://ukshop.economist.com/products/the-economist-style-guide-12th-edition-e-book |archive-date=23 May 2021 |url-status=live}}</ref> It is also used between hours and minutes in time,<ref name="PunctuationGuide" /> between certain elements in [[medical journal]] citations,<ref>{{Citation |title=International Committee of Medical Journal Editors (ICMJE) Uniform Requirements for Manuscripts Submitted to Biomedical Journals: Sample References |url=https://www.nlm.nih.gov/bsd/uniform_requirements.html |access-date=1 March 2013 |archive-url=https://web.archive.org/web/20200217002459/https://www.nlm.nih.gov/bsd/uniform_requirements.html |archive-date=17 February 2020 |url-status=live |publisher=[[United States National Library of Medicine]]}}</ref> between [[chapters and verses of the Bible|chapter and verse]] in [[Bible citation]]s,<ref>{{cite web |title=How to Cite the Bible*. Guide for Four Citation Styles: MLA, APA, SBL, CHICAGO |url=https://www.jbu.edu/assets/writing-center/resource/how_to_cite_the_bible.pdf |url-status=dead |archive-url=https://web.archive.org/web/20210928021857/https://www.jbu.edu/assets/writing-center/resource/How_to_Cite_the_Bible.pdf |archive-date=28 September 2021 |access-date=23 May 2021 |website=jbu.edu |publisher=[[John Brown University]]}}</ref> between two numbers in a [[ratio]], and, in the US, for [[salutation]]s in business letters and other formal letters.<ref name="PunctuationGuide" />

==History==
{{Further|Colon (rhetoric)}}
In [[Ancient Greek]], in [[rhetoric]] and [[Meter (poetry)|prosody]], the term {{wikt-lang|grc|κῶλον}} (''{{transliteration|grc|kôlon}}'', {{Literal translation}} 'limb, member of a body') did not refer to punctuation, but to a member or section of a complete thought or passage; see also ''[[Colon (rhetoric)]]''. From this usage, in [[palaeography]], a colon is a clause or group of clauses written as a line in a [[manuscript]].<ref>{{cite encyclopedia |title=Paperback Oxford English Dictionary |publisher=Oxford University Press |url=https://archive.org/details/paperbackoxforde0000unse_n1q8 |access-date=11 October 2025 |date=1 June 2006 |isbn=978-0-19-861424-1 |lccn=2006040125 |oclc=64554623 |ol=7401639M |last2=Sara |first2=Hawker |last3=Julia |first3=Elliott |last1=Catherine |first1=Soanes}}</ref>

In the 3rd century BC, [[Aristophanes of Byzantium]] is alleged to have devised [[Greek punctuation|a punctuation system]], in which the end of such a {{transliteration|grc|kôlon}} was thought to occasion a medium-length breath, and was marked by a [[interpunct|middot]] {{char|[[·]]}}. In practice, evidence is scarce for its early usage, but it was revived later as the ''[[ano teleia]]'', the [[modern Greek]] [[semicolon]].<ref>{{cite web |last=Nicolas |first=Nick |date=2005 |title=Greek Unicode Issues: Punctuation |url=http://www.tlg.uci.edu/~opoudjis/unicode/punctuation.html |url-status=dead |archive-url=https://archive.today/20120806003722/http://www.tlg.uci.edu/~opoudjis/unicode/punctuation.html |archive-date=6 August 2012 |access-date=7 October 2014 |website=tlg.uci.edu}}</ref> Some writers also used a [[two dot punctuation|double dot symbol]] {{char|⁚}}, that later came to be used as a [[full stop]] or to mark a change of speaker. (See also ''[[Greek punctuation|Punctuation in Ancient Greek]]''.)

In 1589, in ''The Arte of English Poesie'', the [[English language|English]] term ''colon'' and the corresponding punctuation mark {{char|:}} is attested:<ref name="arber">{{cite book |url=https://www.digitale-sammlungen.de/en/view/bsb10748543 |title=The Arte of English Poesie: 1589 |date=1869 |publisher=Alex. Murray & Son |editor1-last=Arber |editor1-first=Edward |editor1-link=Edward Arber |location=London |page=[https://www.digitale-sammlungen.de/en/view/bsb10748543?page=96,97 88] |access-date=26 October 2022 |archive-url=https://web.archive.org/web/20221026184916/https://www.digitale-sammlungen.de/en/view/bsb10748543 |archive-date=26 October 2022 |url-status=live}}</ref>{{efn|The work was published anonymously and attributed to [[George Puttenham]] in reprints.{{r |arber}}}}
{{Blockquote|For these respectes the auncient reformers of language, inuented, three maner of pauses [...] The shortest pause or intermission they called ''comma'' [...] The second they called ''colon'', not a peece but as it were a member for his larger length, because it occupied twise as much time as the comma. The third they called ''periodus'', [...]}}

In 1622, in [[Nicholas Okes]]' print of [[William Shakespeare]]'s ''[[Othello]]'', the typographical construction of a colon followed by a [[hyphen]] or [[dash]] to indicate a restful pause is attested.<ref>{{cite book |url=https://archive.org/details/firstquartoofoth0000shak |title=The first quarto of Othello |date=2001 |publisher=Cambridge University Press |isbn=978-0-521-56257-7 |editor1-last=McMillin |editor1-first=Scott |location=United Kingdom |page=[https://archive.org/details/firstquartoofoth0000shak/page/22 22]}}</ref> This construction, known as the ''[[dog's bollocks (typography)|dog's bollocks]]'', was once common in [[British English]], though this usage is now discouraged.<ref>{{cite web |last1=Dean |first1=Paul |date=25 April 2008 |title=Extreme Type Terminology Part 4: Numerals and Punctuation |url=http://ilovetypography.com/2008/04/25/extreme-type-terminology-part-4/ |url-status=live |archive-url=https://web.archive.org/web/20141119203833/http://ilovetypography.com/2008/04/25/extreme-type-terminology-part-4/ |archive-date=19 November 2014 |access-date=28 November 2014 |website=I Love Typography}}</ref><ref>{{cite web |last1=Martens |first1=Nick |date=20 January 2010 |title=The Secret History of Typography in the Oxford English Dictionary |url=http://bygonebureau.com/2010/01/20/the-secret-history-of-typography-in-the-oxford-english-dictionary/ |url-status=dead |archive-url=https://web.archive.org/web/20141122150147/http://bygonebureau.com/2010/01/20/the-secret-history-of-typography-in-the-oxford-english-dictionary/ |archive-date=22 November 2014 |access-date=28 November 2014 |website=The Bygone Bureau}}</ref><ref name="Trask1997">{{cite web |last1=Trask |first1=Larry |author1-link=Larry Trask |date=1997 |title=The Colon |url=http://www.sussex.ac.uk/informatics/punctuation/colonandsemi/colon |url-status=live |archive-url=https://web.archive.org/web/20180116232539/http://www.sussex.ac.uk/informatics/punctuation/colonandsemi/colon |archive-date=16 January 2018 |access-date=28 November 2014 |work=Guide to Punctuation |publisher=University of Sussex}}</ref>

As late as the 18th century, [[John Mason (minister)|John Mason]] related the appropriateness of a colon to the length of the pause taken when reading the text aloud, but [[silent reading]] eventually replaced this with other considerations.<ref>{{cite web |last=Mason |first=John |author-link=John Mason (minister) |date=1748 |title=An Essay on Elocution |url=https://archive.org/details/essayonelocution00kirk |lccn=70367350 |oclc=37255 |ol=6384113W |quote=A Comma Stops the Voice while we may privately tell one, a Semi Colon two; a Colon three: and a Period four. |location=Menston, Yorks.}}</ref>

==Usage in English==
In modern English usage, a complete sentence precedes a colon, while a list, description, explanation, or definition follows it. The elements which follow the colon may or may not be a complete sentence: since the colon is preceded by a sentence, it is a complete sentence whether what follows the colon is another sentence or not. While it is acceptable to capitalise the first letter after the colon in American English, it is not the case in British English, except where a proper noun immediately follows a colon.<ref>{{cite web |date=20 September 2017 |title=Colons: How to Use Them |url=https://style.mla.org/colons-how-to-use-them/ |url-status=live |archive-url=https://web.archive.org/web/20200810054447/https://style.mla.org/colons-how-to-use-them/ |archive-date=10 August 2020 |access-date=17 August 2020 |website=The MLA Style Center |language=en-US}}</ref>

;Colon used before list
:''Daequan was so hungry that he ate everything in the house: chips, cold pizza, pretzels and dip, hot dogs, peanut butter, and candy.''

;Colon used before a description
:''Bertha is so desperate that she'll date anyone, even William: he's uglier than a squashed toad on the highway, and that's on his good days.''

;Colon before definition
:''For years while I was reading Shakespeare's ''Othello'' and criticism on it, I had to constantly look up the word "egregious" since the villain uses that word: outstandingly bad or shocking.''

;Colon before explanation
:''I guess I can say I had a rough weekend: I had chest pain and spent all Saturday and Sunday in the emergency room.''

Some writers use fragments (incomplete sentences) before a colon for emphasis or stylistic preferences (to show a character's voice in literature), as in this example:
:''Dinner: chips and juice. What a well-rounded diet I have.''

''[[The Bedford Handbook]]'' describes several uses of a colon. For example, one can use a colon after an independent clause to direct attention to a list, an [[appositive]], or a quotation, and it can be used between independent clauses if the second summarizes or explains the first. In non-literary or non-expository uses, one may use a colon after the salutation in a formal letter, to indicate hours and minutes, to show proportions, between a title and subtitle, and between city and publisher in bibliographic entries.<ref>{{cite book |last1=Hacker |first1=Diana |url=https://archive.org/details/bedfordhandbookw00hack |title=The Bedford Handbook |publisher=Bedford/St. Martin's |year=2010 |isbn=978-0-312-65269-2 |location=Boston-New York |pages=[https://archive.org/details/bedfordhandbookw00hack/page/n433 384]–387 |url-access=limited}}</ref>

[[Luca Serianni]], an Italian scholar who helped to define and develop the colon as a punctuation mark, identified four punctuational modes for it: ''syntactical-deductive'', ''syntactical-descriptive'', ''appositive'', and ''segmental''.<ref>{{cite book |last1=Serianni |first1=Luca |author1-link=Luca Serianni |title=Grammatica italiana. Italiano comune e lingua letteraria. Suoni, forme, costrutti |last2=Castelvecchi |first2=Alberto |publisher=UTET |year=1988 |isbn=88-02-04154-7 |location=[[Turin]] |language=it}}</ref>

===Syntactical-deductive===
The colon introduces the [[logical consequence]], or effect, of a fact stated before.

:''There was only one possible explanation: the train had never arrived.''

===Syntactical-descriptive===
In this sense the colon introduces a description; in particular, it makes explicit the elements of a set.
:''I have three sisters: Daphne, Rose, and Suzanne.''

Syntactical-descriptive colons may separate the numbers indicating [[hour]]s, [[minute]]s, and [[second]]s in abbreviated measures of time.<ref>{{cite ISO standard |csnumber=40874 |title=Data elements and interchange formats – Information interchange – Representation of dates and times}}</ref>
:''The concert begins at 21:45.''
:''The rocket launched at 09:15:05.''

[[British English]] and [[Australian English]], however, more frequently use a [[decimal mark|point]] for this purpose:
:''The programme will begin at 8.00 pm.''
:''You will need to arrive by 14.30.''<ref name="Trask1997"/><ref>{{Cite book |last1=Peters |first1=Pam |title=The Cambridge Australian English style guide |date=1995 |publisher=Cambridge University Press |isbn=978-0-521-43401-0 |editor1-last=Grayston |editor1-first=Graham |location=Cambridge |page=146}}</ref>

A colon is also used in the descriptive location of a book verse if the book is divided into verses, such as in the [[Bible]] or the [[Quran]]:
:"Isaiah 42:8"
:"Deuteronomy 32:39"
:"Quran 10:5"

===Appositive===
:''Luruns could not speak: he was drunk.''<ref>Example quoted in [https://web.archive.org/web/20061209020735/http://eatsshootsandleaves.com/eslguide.pdf ''An Educational Companion to ''Eats, Shoots & Leaves] by Lynne Truss</ref>

An appositive colon also separates the [[subtitle (titling)|subtitle]] of a work from its principal title. (In effect, the example given above illustrates an appositive use of the colon as an abbreviation for the conjunction "because".) Dillon has noted the impact of colons on scholarly articles,<ref>{{cite journal |last1=Dillon |first1=J. T. |date=1981 |title=The emergence of the colon: An empirical correlate of scholarship. |journal=American Psychologist |volume=36 |issue=8 |pages=879–884 |doi=10.1037/0003-066x.36.8.879}}</ref><ref>{{cite journal |last1=Dillon |first1=J. T. |date=1982 |title=In Pursuit of the Colon: A Century of Scholarly Progress: 1880–1980 |journal=The Journal of Higher Education |volume=53 |issue=1 |pages=93–99 |doi=10.2307/1981541 |jstor=1981541}}</ref> but the reliability of colons as a predictor of quality or impact has also been challenged.<ref>{{cite journal |last1=Townsend |first1=Michael A.R. |date=1983 |title=Titular Colonicity and Scholarship: New Zealand Research and Scholarly Impact |url=http://www.psychology.org.nz/wp-content/uploads/NZJP-Vol121-1983-7-Townsend.pdf |url-status=live |journal=New Zealand Journal of Psychology |volume=12 |pages=41–43 |archive-url=https://web.archive.org/web/20170409003450/http://www.psychology.org.nz/wp-content/uploads/NZJP-Vol121-1983-7-Townsend.pdf |archive-date=9 April 2017 |access-date=20 April 2017}}</ref><ref>{{cite journal |last1=Lupo |first1=James |last2=Kopelman |first2=Richard E. |date=1987 |title=Punctuation and publishability: A reexamination of the colon. |journal=American Psychologist |volume=42 |issue=5 |pages=513 |doi=10.1037/0003-066x.42.5.513.a}}</ref> In titles, neither needs to be a complete sentence as titles do not represent [[wikt:expository|expository]] writing:

:''Star Wars Episode VI: Return of the Jedi''

===Segmental===

Like a [[dash]] or [[quotation mark]], a segmental colon introduces [[speech]]. The segmental function was once a common means of indicating an unmarked quotation on the same line. The following example is from the grammar book ''[[The King's English]]'':

:''Benjamin Franklin proclaimed the virtue of frugality: A penny saved is a penny earned.''

This form is still used in British industry-standard templates for written performance [[dialogue]]s, such as in a [[play (theatre)|play]].<ref>{{cite web |title=Playscript template |url=https://www.nycplaywrights.org/p/playscript-template.html |url-status=live |archive-url=https://web.archive.org/web/20230313163929/https://www.nycplaywrights.org/p/playscript-template.html |archive-date=13 March 2023 |access-date=13 March 2023}}</ref> The colon indicates that the words following an character's name are spoken by that character.

:''Patient: Doctor, I feel like a pair of curtains.''
:''Doctor: Pull yourself together!''
The uniform visual pattern of <code>&lt;character_nametag : character_spoken_lines></code> placement on a script page assists an actor in scanning for the lines of their assigned character during rehearsal, especially if a script is undergoing rewrites between rehearsals.

===Use of capitals===
Use of capitalization or lowercase after a colon varies. In [[British English]], and in most [[Commonwealth of Nations|Commonwealth]] countries, the word following the colon is in lowercase unless it is normally capitalized for some other reason, as with [[proper noun]]s and [[acronym]]s. British English also capitalizes a new sentence introduced by a colon's [[#Segmental|segmental use]].{{citation needed|date=January 2024}}

[[American English]] permits writers to similarly capitalize the first word of any [[independent clause]] following a colon. This follows the guidelines of some modern American style guides, including those published by the [[Associated Press]] and the [[Modern Language Association]]. ''[[The Chicago Manual of Style]]'', however, requires capitalization only when the colon introduces a direct quotation, a direct question, or two or more complete sentences.<ref>{{cite web |title=Chicago Style Q&A: Capitalization |url=http://www.chicagomanualofstyle.org/qanda/data/faq/topics/Capitalization.html |url-status=live |archive-url=https://web.archive.org/web/20121015022853/http://www.chicagomanualofstyle.org/qanda/data/faq/topics/Capitalization.html |archive-date=15 October 2012 |access-date=8 November 2011 |publisher=Chicagomanualofstyle.org}}</ref>{{failed verification|date=January 2024}}

In many [[Europe]]an languages, the colon is usually followed by a lowercase letter unless the upper case is required for other reasons, as with British English. [[German language|German]] usage requires capitalization of [[independent clause]]s following a colon.<ref>[https://web.archive.org/web/20071012100137/http://www.duden.de/deutsche_sprache/newsletter/archiv.php?id=21 Duden Newsletter vom 24 August 2001]</ref> [[Dutch language|Dutch]] further capitalizes the first word of any quotation following a colon, even if it is not a complete sentence on its own.<ref>{{cite web |title=Hoofdletter na dubbele punt |url=http://taaladvies.net/taal/advies/vraag/392/ |url-status=live |archive-url=https://web.archive.org/web/20111026015501/http://taaladvies.net/taal/advies/vraag/392 |archive-date=26 October 2011 |access-date=8 November 2011 |publisher=taaladvies.net}}</ref>

===Spacing and parentheses===
{{See also|Sentence spacing}}
In print, a thin space was traditionally placed before a colon and a thick space after it. In modern [[English-language]] printing, no space is placed before a colon and a single space is placed after it.<ref>{{cite book |last1=DeRespinis |first1=Francis |title=The IBM Style Guide: Conventions for Writers and Editors |last2=Hayward |first2=Peter |last3=Jenkins |first3=Jana |last4=Laird |first4=Amy |last5=McDonald |first5=Leslie |last6=Radzinski |first6=Eric |date=2012 |publisher=IBM Press |location=Boston |page=43}}</ref><ref>{{cite book |last1=Gibaldi |first1=Joseph |title=MLA Style Manual and Guide to Scholarly Publishing |date=2008 |publisher=Modern Language Association of America |location=New York |page=91}}</ref> In [[French language|French-language]] typing and printing, the traditional rules are preserved.

One or two spaces may be and have been used after a colon. The older convention (designed to be used by [[monospaced font]]s) was to use ''two'' spaces after a colon.<ref>{{cite web |last1=Paterson |first1=Derek |date=19 November 2009 |title=How many spaces after a colon? |url=http://absolutewrite.com/forums/showthread.php?p=4279434#post4279434 |url-status=live |archive-url=https://web.archive.org/web/20130927105919/http://absolutewrite.com/forums/showthread.php?p=4279434#post4279434 |archive-date=27 September 2013 |access-date=4 November 2012 |work=Absolute Write forums |at=Post 4 |quote=Back in the typewriter day, when fading ink ribbons could result in commas being mistaken for periods and vice versa, typists were taught to insert 2 spaces after the period to differentiate between the two. The same happened with colons and semicolons: 2 spaces were left after a colon; 1 space after a semicolon.}}</ref>

In modern typography, a colon will be placed outside the closing [[parenthesis]] introducing a list. In very early English typography, it could be placed inside, as seen in [[Roger Williams]]' 1643 book about the Native American languages of New England.<ref>{{cite web |year=1643 |title=A key into the language of America |url=https://archive.org/details/keyintolanguageo04will/page/52/mode/2up}}</ref>

==Usage in other languages==

===Suffix separator===
In [[Finnish language|Finnish]] and [[Swedish language|Swedish]], the colon can appear inside words in a manner similar to the [[apostrophe]] in the English [[possessive case]], connecting a grammatical [[suffix]] to an [[abbreviation]] or [[initialism]], a special symbol, or a [[Numerical digit|digit]] (e.g., Finnish ''USA:n'' and Swedish ''USA:s'' for the [[genitive case]] of "USA", Finnish ''%:ssa'' for the [[inessive case]] of "%", or Finnish ''20:een'' for the [[illative case]] of "20").

===Abbreviation mark===
Written Swedish uses colons in [[contraction (grammar)|contractions]], such as ''S:t'' for ''Sankt'' (Swedish for "Saint") – for example in the name of the [[Stockholm metro]] station ''[[Sankt Eriksplan metro station|S:t Eriksplan]]'', and ''k:a'' for ''kyrka'' ("church") – for instance [[Svenska kyrkan|Svenska k:a]] (Svenska kyrkan), the Evangelical Lutheran national Church of Sweden. This can even occur in people's names, for example [[Antonia Ax:son Johnson]] (''[[Ax:son Johnson family|Ax:son]]'' for ''Axelson''). [[Early Modern English]] texts also used colons to mark abbreviations.<ref>{{cite book |last1=Ioppolo |first1=Grace |url=https://books.google.com/books?id=wbZHFFvA9eUC&pg=PA73 |title=Dramatists and their manuscripts in the age of Shakespeare, Jonson, Middleton and Heywood |publisher=Psychology Press |year=2006 |isbn=978-0-203-44942-4 |page=73}}</ref><ref>Compare: {{cite book |url=https://books.google.com/books?id=DO5vQXpdJHIC&pg=PA460 |title=Elizabeth I: translations, 1544–1589 |publisher=University of Chicago Press |year=2009 |isbn=978-0-226-20133-7 |editor1-last=Mueller |editor1-first=Janel |page=460 |quote=In the medieval and early modern eras, [...] the colon and raised dot [...] signal a contracted word [...]. |editor2-last=Scodel |editor2-first=Joshua}}</ref>

===Word separator===
[[File:Ethiopic genesis (ch. 29, v. 11-16), 15th century (The S.S. Teacher's Edition-The Holy Bible - Plate XII, 1).jpg|thumb|15th century Bible text in Ge'ez script showing colons between the words]]
In [[Ethiopia]], both [[Amharic]] and [[Ge'ez script]] used and sometimes still use a [[Geʽez script#Punctuation|colon-like mark]] as [[word separator]].

Historically, a colon-like mark was used as a word separator in [[Old Turkic script]].

===End of sentence or verse===
In [[Armenian language|Armenian]], a colon indicates the end of a sentence, similar to a Latin [[full stop]] or period.

In liturgical [[Hebrew punctuation|Hebrew]], the [[sof passuk|sof pasuq]] is used in some writings such as prayer books to signal the end of a verse.

===Score divider===
In [[German language|German]], [[Hebrew language|Hebrew]], and sometimes in [[English language|English]], a colon divides the scores of opponents in sports and games. A result of [[AS Adema 149–0 SO l'Emyrne|149–0]] would be written as 149 : 0 in German and in Hebrew.

==Mathematics and logic<!--'Such that' redirects here-->==
{{Multiple issues|section=yes|
{{More citations needed|section|date=January 2018}}
{{Original research|section|date=January 2018}}
}}
The colon is used in [[mathematics]], [[cartography]], [[scale model|model building]], and other fields, in this context it denotes a [[ratio]] or a [[scale (ratio)|scale]], as in 3:1 (pronounced "three to one").<ref name="PunctuationGuide" />

When a ratio is [[reduction (mathematics)|reduced]] to a simpler form, such as 10:15 to 2:3, this may be expressed with a [[double colon (disambiguation)|double colon]] as 10:15::2:3; this would be read "10 is to 15 as 2 is to 3". This form is also used in tests of logic where the question of "Dog is to Puppy as Cat is to _____?" can be expressed as "Dog:Puppy::Cat:_____". For these uses, there is a dedicated [[Unicode]] symbol ({{unichar|2236}}) that is preferred in some contexts. Compare {{not a typo|2:3}} (ratio colon) with 2:3 (U+003A ASCII colon).

In some languages (e.g. German, Russian, and French), the colon is the commonly used sign for division (instead of ÷).
{{Crossreference|(See also [[Division sign]] and {{section link|Division (mathematics)|Notation}}.)}}

The notation <math>|G : H|</math> may also denote the [[index of a subgroup]].

The notation <math>f : X \to Y</math> indicates that {{mvar|f}} is a [[function (mathematics)|function]] with domain {{mvar|X}} and codomain {{mvar|Y}}.

The combination with an equal sign ({{math|≔}}) is used for [[definition]]s.

In [[mathematical logic]], when using [[set-builder notation]] for describing the characterizing property of a [[set (mathematics)|set]], it is used as an alternative to a [[vertical bar]] (which is the [[ISO 31-11]] standard), to mean "'''such that'''". Example:
:<math>S = \{x \in \mathbb{R} : 1 < x < 3 \}</math> (''S'' is the set of all {{mvar|x}} in <math>\mathbb{R}</math> (the [[real number]]s) such that {{mvar|x}} is strictly greater than 1 and strictly smaller than 3)

In older literature on mathematical logic, it is used to indicate how expressions should be bracketed (see [[Glossary of Principia Mathematica|Glossary of ''Principia Mathematica'']]).

In [[type theory]] and [[programming language theory]], the colon sign after a term is used to indicate its type, sometimes as a replacement to the "∈" symbol. Example:
:<math>\lambda x . x \mathrel{:} A \to A </math>.

A colon is also sometimes used to indicate a [[tensor contraction]] involving two indices, and a double colon (::) for a contraction over four indices.

A colon is also used to denote a [[parallel sum]] operation involving two operands (many authors, however, instead use a [[∥]] sign and a few even a [[∗]] for this purpose).

==Computing==
The character was on early typewriters and therefore appeared in most text encodings, such as [[Baudot code]] and [[EBCDIC]]. It was placed at code 58 in [[ASCII]] and from there inherited into Unicode. Unicode also defines several related characters:
* {{unichar|003A}}
* {{unichar|02D0}}, used in [[International Phonetic Alphabet|IPA]].<ref>{{cite web |year=2005 |title=The International Phonetic Alphabet |url=http://weston.ruter.net/projects/ipa-chart/view/ |url-status=live |archive-url=https://archive.today/20120729122639/http://westonruter.github.com/ipa-chart/ |archive-date=29 July 2012 |access-date=27 October 2011 |work=Weston Ruter}}</ref>
* {{unichar|10781}}, IPA modifier-letter.<ref name="L220252">{{cite web |last1=Miller |first1=Kirk |last2=Ashby |first2=Michael |date=8 November 2020 |title=L2/20-252R: Unicode request for IPA modifier-letters (a), pulmonic |url=https://www.unicode.org/L2/L2020/20252r-mod-ipa-a.pdf |url-status=live |archive-url=https://web.archive.org/web/20210730010133/https://www.unicode.org/L2/L2020/20252r-mod-ipa-a.pdf |archive-date=30 July 2021 |access-date=21 September 2022}}</ref>
* {{unichar|02D1}}, used in IPA.
* {{unichar|10782}}, IPA modifier-letter.<ref name="L220252" />
* {{unichar|02F8}}, used by [[Uralic Phonetic Alphabet]].<ref>{{cite web |last1=Everson |first1=Michael |display-authors=etal |date=20 March 2002 |title=L2/02-141: Uralic Phonetic Alphabet characters for the UCS |url=https://www.unicode.org/L2/L2002/02141-n2419-uralic-phonetic.pdf |url-status=live |archive-url=https://web.archive.org/web/20180219081033/https://www.unicode.org/L2/L2002/02141-n2419-uralic-phonetic.pdf |archive-date=19 February 2018}}</ref>
* {{unichar|05C3}}, compatible with right-to-left text.
* {{unichar|2236}}, for mathematical usage.
* {{unichar|2254}}, for use in pretty-printing programming languages.
* {{unichar|2255}}<ref>{{cite web |last1=Whistler |first1=Ken |last2=Freytag |first2=Asmus |date=19 April 2000 |title=L2/00-119: Encoding Additional Mathematical Symbols in Unicode |url=https://www.unicode.org/L2/L2000/00119-math.pdf |url-status=live |archive-url=https://web.archive.org/web/20180219085257/https://www.unicode.org/L2/L2000/00119-math.pdf |archive-date=19 February 2018}}</ref>
* {{unichar|2360}}
* {{unichar|2982}}
* {{unichar|2A74}}
* {{unichar|205D|nlink=}}
* {{unichar|2AF6}}
* {{unichar|A789}}, see [[Colon (letter)]]. (This character is also sometimes used in [[Microsoft Windows|Windows]] [[filename]]s as it is identical to the colon in the [[Segoe UI]] font used for filenames. The colon itself is not permitted as it is a [[reserved character]].)
* {{unichar|FE13}}, compatibility character for the Chinese Standard [[GB 18030]].
* {{unichar|FF1A}}, for compatibility with [[halfwidth and fullwidth forms|halfwidth and fullwidth fonts]].
* {{unichar|FE55}}, compatibility character for the Chinese National Standard [[CNS 11643]].

===Programming languages===
{{See also|Semicolon#Computing}}

Many programming languages, most notably [[ALGOL]], [[Pascal (programming language)|Pascal]] and [[Ada (programming language)|Ada]], use a colon and equals sign {{code|1=:=}} as the [[assignment (computer science)|assignment operator]], to distinguish it from a single equals {{code|1==}} which is an equality test (C instead uses a single equals as assignment, and a double equals {{code|1===}} as the equality test).<ref>{{cite web |date=4 February 2021 |title=Becomes |url=https://wiki.freepascal.org/Becomes |url-status=live |archive-url=https://web.archive.org/web/20220302024707/https://wiki.freepascal.org/Becomes |archive-date=2 March 2022 |website=Free Pascal and Lazarus Wiki}}</ref><ref>{{cite web |year=2012 |title=Ada Reference Manual – 5.2 Assignment Statements |url=http://www.ada-auth.org/standards/rm12_w_tc1/html/RM-5-2.html |url-status=live |archive-url=https://archive.today/20200520204221/http://www.ada-auth.org/standards/rm12_w_tc1/html/RM-5-2.html |archive-date=20 May 2020 |publisher=Ada Conformity Assessment Authority}}</ref>

Many languages including [[C (programming language)|C]] and [[Java (programming language)|Java]] use the colon to indicate the text before it is a [[label (computer science)|label]], such as a target for a [[goto]] or an introduction to a case in a [[switch statement]].<ref name="c99">{{cite web |author=((ISO/IEC JTC1/SC22/WG14)) |date=7 September 2007 |title=ISO/IEC 9899:TC3 – Programming languages – C |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf |url-status=live |archive-url=https://archive.today/20200416164053/http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf |archive-date=16 April 2020}}</ref>{{rp|p=131}}<ref>{{cite web |date=23 February 2022 |title=The Java Language Specification – Chapter 14. Blocks, Statements, and Patterns |url=https://docs.oracle.com/javase/specs/jls/se18/html/jls-14.html |url-status=live |archive-url=https://web.archive.org/web/20220608143908/https://docs.oracle.com/javase/specs/jls/se18/html/jls-14.html |archive-date=8 June 2022 |website=Oracle Help Center |publisher=Oracle}}</ref> In a related use, [[Python (programming language)|Python]] uses a colon to separate a control statement (the ''clause header'') from the block of statements it controls (the ''suite'').<ref>{{cite web |date=22 January 2016 |title=The Python Language Reference – 8. Compound statements |url=https://docs.python.org/3/reference/compound_stmts.html |url-status=live |archive-url=https://archive.today/20160126080617/https://docs.python.org/3/reference/compound_stmts.html |archive-date=26 January 2016 |publisher=Python Software Foundation}}</ref>

In many languages, including [[JavaScript]], colons are used to define [[name–value pair]]s in a [[JSON|dictionary]] or [[Object (computer science)|object]].<ref>{{cite book |author=((ECMA TC39)) |url=https://www.ecma-international.org/wp-content/uploads/ECMA-262_13th_edition_june_2022.pdf |title=ECMA-262 |date=June 2022 |publisher=Ecma International |edition=13th |archive-url=https://web.archive.org/web/20220704012713/https://www.ecma-international.org/wp-content/uploads/ECMA-262_13th_edition_june_2022.pdf |archive-date=4 July 2022 |url-status=live}}</ref>{{rp|pp=96–100}} This is also used by data formats such as [[JSON]].{{Ref RFC|8259}} Some other languages use an equals sign.

The colon is used as part of the [[?:]] conditional operator in C and many other languages.<ref name='c99' />{{rp|p=90}}

[[C++]] and [[Rust (programming language)|Rust]] use a double colon as the [[scope resolution operator]]/[[namespace]] qualification, and [[class member function|class member access]].<ref>{{cite web |date=16 June 2022 |title=Identifiers |url=https://en.cppreference.com/w/cpp/language/identifiers |url-status=live |archive-url=https://web.archive.org/web/20220722004426/https://en.cppreference.com/w/cpp/language/identifiers |archive-date=22 July 2022 |access-date=28 July 2022 |website=C++ Reference}}</ref> This is unlike some other languages, which use periods to do so. Another language using colons for scope resolution is [[Erlang (programming language)|Erlang]], which uses a single colon.<ref>{{cite web |date=15 July 2022 |title=Erlang Reference Manual – Expressions |url=https://www.erlang.org/doc/reference_manual/expressions.html |url-status=live |archive-url=https://web.archive.org/web/20220721195015/https://www.erlang.org/doc/reference_manual/expressions.html |archive-date=21 July 2022 |access-date=28 July 2022 |website=Erlang |publisher=Ericsson}}</ref> In [[C Sharp (programming language)|C#]], the double colon is used to access a member of an aliased namespace.<ref>{{cite web|title=:: operator - the namespace alias operator|url= https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/namespace-alias-qualifier|date=11 April 2023|publisher=Microsoft Learn|website=learn.microsoft.com}}</ref> Similarly in [[Java (programming language)|Java]], the double colon is used to retrieve a method reference.

In [[BASIC]], it is used as a separator between the statements or instructions in a single line. Most other languages use a semicolon, but BASIC had used semicolon to separate items in print statements.<ref>{{cite web |date=15 September 2021 |title=Special Characters in Code (Visual Basic) |url=https://docs.microsoft.com/en-gb/dotnet/visual-basic/programming-guide/program-structure/special-characters-in-code |url-status=live |archive-url=https://web.archive.org/web/20220411195955/https://docs.microsoft.com/en-us/dotnet/visual-basic/programming-guide/program-structure/special-characters-in-code |archive-date=11 April 2022 |website=Microsoft Docs |publisher=Microsoft}}</ref>

In [[Forth (programming language)|Forth]], a colon ''precedes'' definition of a new word.<ref>{{cite web |title=Core: Glossary |url=https://forth-standard.org/standard/core/Colon |url-status=live |archive-url=https://web.archive.org/web/20151117054836/https://forth-standard.org/standard/core/Colon |archive-date=17 November 2015 |website=Forth Standard |publisher=Forth-Standard-Committee}}</ref>

[[Haskell]] uses a colon (pronounced as "[[cons]]", short for "construct") as an operator to add a [[data element]] to the front of a [[List (computing)|list]],<ref>{{cite book |last1=O'Sullivan |first1=Bryan |url=https://book.realworldhaskell.org/read/getting-started.html |title=Getting Started |last2=Stewart |first2=Don |last3=Goerzen |first3=John |date=2007–2008 |publisher=Real World Haskell |access-date=8 November 2011 |archive-url=https://archive.today/20120710090552/http://book.realworldhaskell.org/read/getting-started.html |archive-date=10 July 2012 |url-status=live}}</ref> while a double colon <code>::</code> is read as "has type of" (compare [[Scope resolution operator#Haskell|scope resolution operator]]).<ref>{{cite book |last1=Lipovača |first1=Miran |url=https://learnyouahaskell.com/types-and-typeclasses |title=Learn You a Haskell for Great Good! |date=April 2011 |publisher=No Starch Press |isbn=978-1-59327-283-8 |chapter=Types and Typeclasses |access-date=8 November 2011 |archive-url=https://archive.today/20120710015700/http://learnyouahaskell.com/types-and-typeclasses |archive-date=10 July 2012 |url-status=live}}</ref> The [[ML (programming language)|ML]] languages (such as [[Standard ML]]) have the above reversed, where the double colon (<code>::</code>) is used to add an element to the front of a list; and the single colon (<code>:</code>) is used for type guards.<ref>{{cite book |last1=Milner |first1=Robin |author1-link=Robin Milner |url=https://smlfamily.github.io/sml97-defn.pdf |title=The Definition of Standard ML |last2=Tofte |first2=Mads |author2-link=Mads Tofte |last3=Harper |first3=Robert |author3-link=Robert Harper (computer scientist) |last4=MacQueen |first4=David |publisher=MIT Press |year=1997 |isbn=0-262-63181-4 |edition=Revised |archive-url=https://web.archive.org/web/20200430075159/https://smlfamily.github.io/sml97-defn.pdf |archive-date=30 April 2020 |url-status=live}}</ref>{{rp|pp=20, 70}} Rust, [[ActionScript]], [[Kotlin (programming language)|Kotlin]], and [[TypeScript]] also use a colon to include a type annotation on a function or a variable.

[[MATLAB]] uses the colon as a binary operator to generate a vector, or to select a part of an extant matrix.

[[APL (programming language)|APL]] uses the colon:
* to introduce a [[Control flow|control structure]] element. In this usage it must be the first non-blank character of the line.<ref name="DyalogAPL">{{cite web |date=April 2011 |title=Dyalog APL Language Reference Manual |url=http://docs.dyalog.com/13.0/Dyalog%20APL%20Language%20Reference.v13.0.pdf |url-status=live |archive-url=https://web.archive.org/web/20160304040415/http://docs.dyalog.com/13.0/Dyalog%20APL%20Language%20Reference.v13.0.pdf |archive-date=4 March 2016 |access-date=14 February 2012 |publisher=Dyalog Limited}}</ref>{{Rp|p=64}}
* after a label name that will be the target of a <code>:goto</code> or a right-pointing arrow (this style of programming is deprecated and programs are supposed to use control structures instead).<ref name="DyalogAPL" />{{Rp|p=64}}
* to separate a guard ([[Boolean expression]]) from its expression in a dynamic function.<ref name="DyalogAPL" />{{Rp|p=111}} Two colons are used for an Error guard (one or more error numbers).<ref name="DyalogAPL" />{{Rp|p=115}}
* Colon + space are used in class definitions to indicate inheritance.<ref name="DyalogAPL" />{{Rp|p=135}}
* ⍠ (a colon in a box) is used by APL for its variant operator.<ref name="DyalogAPL" />{{Rp|p=340}}

The colon is also used in many operating systems commands.<ref>{{cite web |year=2018 |title=colon – null utility |url=https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#colon |url-status=live |archive-url=https://archive.today/20181017145503/http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html |archive-date=17 October 2018 |website=IEEE Std 1003.1-2017 |publisher=The Open Group}}</ref>

In the [[esoteric programming language]] [[INTERCAL]], the colon is called ''two-spot'' and used to label a [[32-bit computing|32-bit]] variable, distinct from ''spot'' (.) to label a [[16-bit computing|16-bit]] variable.<ref>{{cite web |last1=Woods |first1=Donald R. |author1-link=Don Woods (programmer) |last2=Lyon |first2=James M. |year=1973 |title=INTERCAL reference manual |url=http://oops.se/~urban/pit/intercal.ps |url-status=dead |archive-url=https://web.archive.org/web/20110716084816/http://oops.se/~urban/pit/intercal.ps |archive-date=16 July 2011 |access-date=10 March 2012 |format=PS}}</ref>{{Rp|p=3}}

===Addresses===
Internet URLs use the colon to separate the protocol (such as {{code|http:}}) from the [[hostname]] or [[IP address]].{{Ref RFC|3986|repeat=yes}}

In an [[IPv6 address#Representation|IPv6 address]], colons (and one optional double colon) separate up to 8 groups of 16 [[bit]]s in [[hexadecimal]] representation.{{Ref RFC|4291}} In a [[URL]], a colon follows the initial scheme name (such as Hypertext Transfer Protocol ([[HTTP]]) and [[File Transfer Protocol]] (FTP), and separates a [[port number]] from the [[hostname]] or [[IP address]].{{Ref RFC|3986}}

In [[Microsoft Windows]] [[filename]]s, the colon is reserved for use in [[fork (file system)#Microsoft|alternate data streams]] and cannot appear in a filename.<ref>{{cite web |date=24 August 2020 |title=[MS-FSCC]: 2.1.5 Pathname |url=https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-fscc/ffb795f3-027d-4a3c-997d-3085f2332f6f |url-status=live |archive-url=https://archive.today/20201022102028/https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-fscc/ffb795f3-027d-4a3c-997d-3085f2332f6f |archive-date=22 October 2020 |website=Microsoft Docs |publisher=Microsoft}}</ref> It was used as the directory separator in [[Classic Mac OS]], and was difficult to use in early versions of the newer [[BSD]]-based [[macOS]] due to code swapping the slash and colon to try to preserve this usage. In most systems it is often difficult to put a colon in a filename as the shell interprets it for other purposes.

[[CP/M]] and early versions of [[MSDOS]] required the colon after the names of devices, such as {{code|CON:}} though this gradually disappeared except for disks (where it had to be between the disk name and the required [[path (computing)|path representation]] of the file as in <code>C:\Windows\</code>). This then migrated to use in [[Uniform Resource Locator|URLs]].{{Ref RFC|3986|repeat=yes}}

===Text markup===
{{Unreferenced section|date=April 2022}}

It is often used as a single post-fix [[delimiter]], signifying a token keyword had immediately preceded it or the transition from one mode of character string interpretation to another related mode. Some applications, such as the widely used [[MediaWiki]], use the colon as both a pre-fix and post-fix delimiter.
<!-- Could work more wikimarkup into that as an example. --><!-- What is this trying to say? -->

In [[wiki markup]], the colon is often used to indent text. Common usage includes separating or marking comments in a discussion as replies, or to distinguish certain parts of a text.

==See also==
* [[Semicolon]] ({{char|;}})
* [[Two dots (disambiguation)]]

==Notes==
{{Notelist}}

==References==
{{Reflist}}

== External links ==
{{Commons category|Colons}}
* {{cite web |title=Using the Colon |url=http://programs.northlandcollege.edu/owl/Colon%20rules.htm |url-status=dead |archive-url=https://web.archive.org/web/20141016001636/http://programs.northlandcollege.edu/owl/Colon%20rules.htm |archive-date=16 October 2014 |access-date=2 December 2013 |website=On-line Writing Lab |publisher=[[Northland Community and Technical College]]}}
* [https://academicguides.waldenu.edu/writingcenter/punctuation/colons Walden University Guides] Punctuation: Colons

{{Navbox punctuation}}
{{Authority control}}

[[Category:Punctuation]]
[[Category:Typographical symbols]]
[[Category:Programming language comparisons]]
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