Colon (punctuation)

A colon (":") is a punctuation mark, visually consisting of two equally sized dots centered on the same vertical line. Rarely, it is also called "dots".

Grammar

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 of thumb, however, a colon informs the reader that what follows proves, clarifies, 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 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
syntactical-descriptive: introduces a description; in particular, explicits the elements of a set
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.

This last was once a common means of indicating an unmarked quotation on the same line (from the Fowlers' grammar book, The King's English)

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

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)

The concert finished at 23:45

This file was last modified today at 11:15:05

separation of a title and the corresponding subtitle

Star Wars A New Hope

separation of clauses in a periodic sentence

In English, a colon may be followed either by a capital letter or by a lower case letter, as the author prefers (unless a capital letter is necessary for a proper noun.) No particular consistency is required within a given text, although it is assumed that use of both capital letters and lower case letters in a single given text would serve some purpose in communicating the author's desired meaning, rather than simply reflecting careless inconsistency.

Conventions and foreign languages

In European languages the colon is usually followed by a lowercase letter (again, unless the uppercase is due to other reasons, such as a proper noun). An exception is German, where an uppercase letter must be used if the colon is followed by a complete sentence or a noun, although in all other cases a lowercase letter should be used.

No space is put before a colon, except in French.

In Finnish, the colon can appear inside words in a manner similar to the English apostrophe, between a word (or abbreviation) and its grammatical suffixes.

Trivia:

Many readers of the Italian writer Italo Svevo are quite surprised at seeing his usage of an uppercase letter after colons. This is not the Italian convention, nor was it at the epoch of writing. Svevo, who lived in an almost bilingual environment, adopts in fact the German usage.

Mathematics

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 logic and, correspondingly, when describing the characterizing property of a set, it is used as an alternative to a vertical bar, to mean "such that". Example:

$S = \{x \in\mathbb{R}: 1 < \; x < \; 3 \}$ $\big($ S is the set of (all and only) x in $\mathbb{R}$ such that x is greater than 1 and smaller than 3 $\big)$

Phonetics

A special triangular colon symbol is used in IPA to indicate a preceding long vowel. Its form is that of two equilateral 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 (). A regular colon is often used as a fallback when this character is not available.

Computing

The colon character has the decimal value 58 (hexadecimal value 3A) in Unicode and ASCII character encodings.

A colon is a special character in URLs and in the path representation of several file systems.

References

Punctuation | Typography