Definitions

# Colon (punctuation)

The colon (“:”) is a punctuation mark, consisting of two equally sized dots centered on the same vertical line.

## Punctuation

### Usage

As with many other punctuation marks, the usage of colon varies among languages and, for a given language, among historical periods. As a rule, however, a colon informs the reader that what follows proves and explains, or simply enumerates elements of what is referred to before.

The following classification of the functions that a colon may have, given by Luca Serianni (a pioneer of the colon) for Italian usage, is generally valid for English and many other languages:

• syntactical-deductive: introduces the logical consequence, or effect, of a fact stated before

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

• syntactical-descriptive: introduces a description—in particular, makes explicit the elements of a set

I have three sisters: Catherine, Sarah and Mary.

• appositive: introduces a sentence with the role of apposition with respect to the previous one
• segmental: introduces a direct speech, in combination with quotation marks and dashes. The segmental function was once a common means of indicating an unmarked quotation on the same line. The following example is from Fowler's grammar book, The King’s English:

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

It is commonly used to introduce speech in a dialogue (such as a script):

Patient: Doctor, I feel like a pair of curtains.
Doctor: Pull yourself together!

A colon may also be used for the following:

• introduction of a definition

A: the first letter in the Latin alphabet
Hypernym of a word: a word having a wider meaning than the given one; e.g., vehicle is a hypernym of car

• separation of the chapter and the verse number(s) indication in many references to religious scriptures, and also epic poems; it was also used for chapter numbers in roman numerals

John 3:14–16 (or John III:14–16) (cf. chapters and verses of the Bible)
The Qur'an, Sura 5:18

• separation when reporting time of the day (cf. ISO 8601); however, this is not universal (but is typically used with American software)

The concert finished at 23:45 (or alternatively 23.45 )

• separation of a title and the corresponding subtitle

In English, a colon may be followed either by a capital letter or by a lower case letter, depending on usage: where speech follows, a capital letter is used; where an acronym or proper noun follows, a capital is used; otherwise a lower case letter is used. In British English, the word following the colon is uncapitalized unless it is a proper noun, an acronym, or if it is normally capitalized for some other reason. Some modern American style guides, including those published by the Associated Press and the Modern Language Association, specify capitalization where the colon is followed by an independent clause (i.e. a complete sentence). However, The Chicago Manual of Style requires capitalization only when the colon introduces two or more complete sentences.

• TAYLOR: You know that I have red hair, Chloe. How many more times?
• He is inordinately proud of one article he created: FRESH, UNESCO arose out of his efforts to disambiguate Fresh
• Julian Duguid, author of Green Hell (1931), starts his book boldly: “When a man yields to the urge of Ishmael . . .”
• This theory isn’t as high-falutin’ as it sounds: De Picciotto is just pointing out that, for a tennis player in an important match, it is much easier to shut out an awareness of the plight of the horned owl than to resist the distractions of personal problems. [Peter Bodo, “The Human Side of Steffi Graf,” Tennis, Sept. 1990, p. 46.]
• To err is human: to forgive, Divine

### Conventions and non-English languages

In many European languages the colon is usually followed by a lowercase letter (unless the uppercase is due to other reasons, such as a proper noun). However, usage differs from this in German, where an uppercase letter may be used only if the sentence after the colon could stand alone without the preceding sentence (elsewise one may judge freely according to the relative independency of the two assertions), and in Dutch, where an uppercase letter must be used if the colon is followed by a quotation or an enumeration of complete sentences, although in all other cases a lowercase letter should be used.

A thin space is traditionally placed before a colon and a thick space after it. In English-language modern high-volume commercial 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 typewriters and same-width fonts [i.e. Courier New]) was to use TWO spaces after a colon. The newer convention (designed for digital systems and different-width fonts [i.e. Arial and Times New Roman]) is that ONE space is sufficient.

## History

English colon is from Latin colon (plural cola), itself from Greek κῶλον "limb, member, portion", in rhetorics or prosody especially a part or section of a sentence or a rhythmical period of an utterance. In paleography, a colon is a clause or group of clauses written as a line. The OED cites William Blades' The life and typography of W. Caxton (1882), p. 126: "The Greek grammarians [...] called a complete sentence a period, a limb was a colon, and a clause a comma." Use of the : symbol to mark the discontinuity of a grammatical construction, or a pause of a length intermediate between that of a semicolon and that of a period, was introduced in English orthography around 1600. John Bullokar, An English expositor (1616) glosses Colon as "A marke of a sentence not fully ended which is made with two prickes."

John Mason in An essay on elocution (1748) prescribes "A Comma Stops the Voice while we may privately tell one, a Semi Colon two; a Colon three: and a Period four."

## Diacritical usage

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 bit larger than a point 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 (particularly in Mexico) which have a phonemic long/short distinction in vowels.

## Word-medial separator

In Finnish and Swedish, the colon can appear inside words in a manner similar to the English apostrophe, between a word (or abbreviation, especially an acronym) and its grammatical (mostly genitive) suffixes. In Swedish, it also occurs in names, for example son Johnson (Ax:son for Axelson). In Finnish it is used in loanwords and abbreviations; e.g., USA:han for the illative case of "USA". For loanwords ending orthographically in a consonant but phonetically in a vowel, the apostrophe is used instead: e.g. show'n for the genitive case of the English loan "show" or Versailles'n for the French place name Versailles.

## Mathematics and logic

The colon is also used in mathematics, cartography, model building and other fields to denote a ratio or a scale, as in 3:1 (pronounced “three to one”). Unicode provides a distinct ratio character, Unicode U+2236 (∶) for mathematical usage.

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, to mean “such that”. Example:

$S = \left\{x in mathbb\left\{R\right\}colon 1 < x < 3 \right\}$ (S is the set of all x in $mathbb\left\{R\right\}$ such that x is strictly greater than 1 and strictly smaller than 3)

The colon is used as a division sign: “a divided by b” is written as a : b, or to denote a ratio.

The combination with an equal sign, $:=,$, is used for definitions.

## Computing

In computing, the colon character is represented by ASCII code 58, and is located at Unicode code-point U+003A. The full-width (double-byte) equivalent, , is located at Unicode code point U+FF1A.

The colon is quite often used as a special control character in many operating systems commands, URLs, computer programming languages, and in the path representation of several file systems. 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.

Several programming languages use the colon for various purposes. In particular, Matlab uses the colon as an binary operator that generates vectors, as well as to select particular portions of existing matrices.

For a double colon see Paamayim Nekudotayim.

## Internet usage

On the Internet (online chats, email, message boards, etc.) a colon, or multiple colons, is sometimes used to denote an action or to emote. In this use it has the inverse function of quotation marks, denoting actions where unmarked text is assumed to be dialog. 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. :Click: Compare to the use of the asterisk.

It also has the widespread usage of representing two vertically aligned eyes in a emoticon, such as :-), :), :(:P, :D, :O, etc.