Colon (punctuation)

The colon ( : ) is a punctuation mark consisting of two equally sized dots centered on the same vertical line. A colon precedes an explanation, or an enumeration, or list. A colon is also used with ratios, titles and subtitles of books, city and publisher in bibliographies, Biblical citations between chapter and verse, and—in American English—to separate hours and minutes, for business letter salutations and in formal letter writing.^[1]

In Unicode, it is encoded at U+003A : COLON (HTML :). Its alt code is alt+58.^[2]

Usage

The most common use of the colon is to inform the reader that what follows the colon proves, explains, defines, describes, or lists elements of what preceded it. In modern American 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 capitalize the first letter after the colon in American English, British English does not.^[3]

colon used before list

Williams was so hungry he ate everything in the house: chips, cold pizza, pretzels and dip, hot dogs, peanut butter and candy.

colon used before a description

Jane is so desperate that she'll date anyone, even Tom: 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 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.^[4]

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.^[5] Although Serianni wrote this guide for the Italian language, his definitions apply also to English and many other languages.

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 hours, minutes, and seconds in abbreviated measures of time.^[6]

The concert begins at 21:45.

The rocket launched at 09:15:05.

British English, however, more frequently uses a full stop for this purpose:

The programme will begin at 8.00 pm.

You will need to arrive by 14.30.^[7]

Appositive

Luruns could not speak: he was drunk.^[8]

An appositive colon also separates the subtitle of a work from its principal title. In titles, neither needs to be a complete sentence as titles do not represent 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 written dialogues, such as in a play. The colon indicates that the words following an individual's name are spoken by that individual.

Patient: Doctor, I feel like a pair of curtains.

Doctor: Pull yourself together!

Use of capitals

Use of capitalization or lower-case after a colon varies. In British English, the word following the colon is in lower case unless it is normally capitalized for some other reason, as with proper nouns and acronyms. British English also capitalizes a new sentence introduced by colon's segmental use; American English goes further and 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,^[9] however, requires capitalization only when the colon introduces a direct quotation or two or more complete sentences.^[10]

In many European languages, the colon is usually followed by a lower-case letter unless the upper case is required for other reasons, as with British English. German usage requires capitalization of independent clauses following a colon.^[11] Dutch further capitalizes the first word of any quotation following a colon, even if it is not a complete sentence on its own.^[12]

Spacing

In print, a thin space is 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. In 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 fonts) was to use two spaces after a colon.^[13]

History

The English word "colon" is from Latin colon (pl. cola), itself from Ancient Greek κῶλον, meaning "limb", "member", or "portion". In Greek rhetoric and prosody, the term did not refer to punctuation but to the expression or passage itself. A "colon" was section of a complete thought or passage. From this usage, in palaeography, a colon is a clause or group of clauses written as a line in a manuscript.^[14] In the punctuation system devised by Aristophanes of Byzantium in the 3rd century BC, the end of such a clause was thought to occasion a medium-length breath and was marked by a middot ⟨·⟩. (This was only intermittently used, but eventually revived as the ano teleia, the modern Greek semicolon.^[15]) A double dot symbol ⟨⁚⟩, meanwhile, later came to be used as a full stop or to mark a change of speaker. A variant was introduced to English orthography around 1600, marking a pause intermediate between a comma and a period.^[16] As late as the 18th century, the appropriateness of a colon was still being related to the length of the pause taken when reading the text aloud, but silent reading eventually replaced this with other considerations.^[17]

In British English, it was once common for a colon to be followed by a hyphen or dash to indicate a restful pause, in a typographical construction known as the "dog's bollocks", though this usage is now discouraged.^[18][19][20]

International Phonetic Alphabet

A special triangular colon symbol is used in IPA to indicate that the preceding sound is long. Its form is that of two triangles, each a little larger than a point (dot) of a standard colon, pointing toward each other. It is available in Unicode as modifier letter triangular colon, Unicode U+02D0 (ː). A regular colon is often used as a fallback when this character is not available, and in the practical orthography of some languages which have a phonemic long/short distinction in vowels.

If the upper triangle is used without the lower one (modifier letter half triangular colon, Unicode U+02D1: ⟨ˑ⟩), it designates a "half-long" vowel.^[21]

Word-medial separator

In Finnish and 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 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

In Swedish, the colon is used in contractions, such as S:t for Sankt (Swedish for "Saint"), e.g. in the Stockholm metro station S:t Eriksplan. This can even occur in people's names, for example Antonia Ax:son Johnson (Ax:son for Axelson). The colon was also used to mark abbreviations in early modern English.^[22][23]

Letter

The colon is also used as a grammatical tone letter in Budu in the Democratic Republic of the Congo, in Sabaot in Kenya, in some Grebo in Liberia, and in Papua New Guinea: Erima, Gizra, Go꞉bosi, Gwahatike, Kaluli, Kamula, Kasua, Kuni-Boazi, and Zimakani.^[24] The Unicode character used for the tone letter U+A789 ꞉ MODIFIER LETTER COLON is different from the punctuation (U+003A), as well from IPA's triangular colon U+02D0.

Mathematics and logic

The colon is used in mathematics, cartography, model building, and other fields—in this context it denotes a ratio or a scale, as in 3:1 (pronounced "three to one"). When a ratio is reduced to a simpler form, such as 10:15 to 2:3, this may be expressed with a 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:_____". Unicode provides a distinct character U+2236 ∶ RATIO for mathematical usage. In some languages (e.g. German), the colon is the commonly used sign for division (instead of ÷).

The notation |G : H| may also denote the index of a subgroup.

The notation ƒ: X → Y indicates that f is a function with domain X and codomain Y.

The combination with an equal sign (≔) is used for definitions.

In mathematical logic, when using set-builder notation for describing the characterizing property of a set, it is used as an alternative to a vertical bar (which is the ISO 31-11 standard), to mean "such that". Example:

(S is the set of all x in (the real numbers) such that x is strictly greater than 1 and strictly smaller than 3)

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:

Some languages like Haskell use a double colon (::) to indicate type instead.

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

Computing

In computing, the colon character is represented by ASCII code 58, (HTML :) and is located at Unicode code-point U+003A (colon). Scripts comprising wide characters, such as kanji, use a full-width equivalent, located at Unicode code point U+FF1A ： FULLWIDTH COLON (HTML ：).

Several programming languages use the colon for various purposes.

A number of programming languages, most notably Pascal and Ada, use a colon immediately followed by an equality sign (:=), in which case the colon and the equality sign are considering to compose to an independent assignment sign; this can be represented in Unicode as U+2254 ≔ COLON EQUALS (HTML ≔).

Labels—targets for jumps, notably goto, but also some switch statements—are general formed of a label name followed by a colon. These includes C and DOS batch files.

For the double colon used in computer programming, see the scope resolution operator, and class member access of C++.

The colon is also used as part of the ?: conditional operator in C and other languages.

In a number of languages, including JavaScript and Python, colons are used to define name-value pairs in a dictionary or object.

var obj = {
    name: "Charles",
    age: 18,
}

The colon is also used in many operating systems commands. 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, utilize the colon as both a pre-fix and post-fix delimiter.

In wiki markup, the colon is often used to indent text. Common usage includes separating or marking comments in a discussion as replies (see WP:INDENT), or to distinguish certain parts of a text.

Normal text.
:Dented text by the means of a colon.
::The gap increases with colon number.

Addresses

The colon is quite often used as a special control character in URLs,^[25] computer programming languages, in the path representation of several file systems (such as FAT, following the drive letter, as in C:\Windows\, and HFS).

In an IPv6 address colons (and one optional double colon) separate up to 8 groups of 16 bits in hexadecimal representation.^[26] In a URL a colon follows the initial scheme name (such as HTTP and FTP), and separates a port number from the hostname or IP address.^[25]

Other languages

In BASIC, it is used as a separator between the statements or instructions in a single line, which is represented in other languages via the semicolon.

In Forth, a colon precedes definition of a new word.

Haskell uses a colon (pronounced as "cons", short for "construct") as an operator to add an element to the front of a list:^[27]

"child" : ["woman", "man"] -- returns ["child","woman","man"]

while a double colon :: is read as "has type of" (confer scope resolution operator):^[28]

("text", False) :: ([Char], Bool)

The ML languages (including Standard ML and OCaml) have the above reversed, where the double colon (::) is used to add an element to the front of a list; and the single colon (:) is used for type guards.

MATLAB uses the colon as a binary operator that generates vectors, as well as to select particular portions of existing matrices.

In Python, which uses indentation to indicate blocks, the colon is used in statements to indicate that the next line is the start of an indented block.

APL uses the colon^[29]

• to introduce a control structure element. In this usage it must be the first non-blank character of the line.
• after a label name that will be the target of a :goto or a right-pointing arrow (Note: this style of programming is deprecated and programmers are encouraged to use control structures instead).
• to separate a guard (boolean expression) from its expression in a dynamic function. Two colons are used for an Error guard (one or more error numbers).
• Colon + space are used in class definitions to indicate inheritance.

In the esoteric programming language INTERCAL, the colon is called "two-spot" and is used to identify a 32-bit variable—distinct from a spot (.) which identifies a 16-bit variable.

Internet usage

On the Internet, a colon, or multiple colons, is sometimes used to denote an action (similar to how asterisks are used) or to emote (for example, in vBulletin). In the action denotation usage it has the inverse function of quotation marks, denoting actions where unmarked text is assumed to be dialogue. For example:

Tom: Pluto is so small; it should not be considered a planet. It is tiny!

Mark: Oh really? ::drops Pluto on Tom's head:: Still think it’s small now?

Colons may also be used for sounds, e.g., ::click::, though sounds can also be denoted by asterisks or other punctuation marks.

Colons can also be used to represent eyes in emoticons.

Encoding

• U+003A  :  COLON (HTML :)

• U+FF1A  ：  FULL-WIDTH COLON (HTML ：)

• U+02D0  ː  IPA TRIANGULAR COLON  (HTML ː)

References

External links

Wikimedia Commons has media related to Colons.

• "Using the Colon". On-line Writing Lab. Northland Community and Technical College. Retrieved 2 December 2013.