PUNCTUATION - Colons

Use of Colon

A colon informs the reader that what follows the mark proves, explains, or lists elements of what preceded the mark.

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.

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.

Ex:"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.

Ex: "I have three sisters: Catherine, Sarah, and Mary."

The syntactical-descriptive applies to the separation of the hour, minute, and second in abbreviated measures of time.

Ex: The concert begins at 21:45.
The rocket launched at 09:15:05.

Similarly, the syntactical-descriptive colon separates chapter and verse numbers in citations of passages in widely-studied texts, such as epic poetry, religious texts, and the plays of William Shakespeare.

Ex: John 3:14–16 or John III:14–16 refers to verses 14 through 16 of chapter three of the Gospel of John.


Appositive

The colon introduces an appositive independent clause. In other words, the sentence after the colon is in apposition to the one before the colon.

Ex: "Luruns could not speak: He was drunk."

An appositive colon also separates the subtitle of a work (which is a noun phrase) from its principal title (another noun phrase).

Ex: Star Wars Episode IV: A New Hope


Segmental

A segmental colon, like a dash or quotation mark, 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:

Ex: "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.


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 a proper noun or an acronym, or if it is normally capitalized for some other reason. However, in American English, many writers capitalize the word following a colon if it begins an independent clause (i.e., a complete sentence). 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 or two or more complete sentences.

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


Spacing

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 monospaced fonts) was to use two spaces after a colon. The newer convention (designed for proportional fonts) is that one space is sufficient. See also Double spacing at the end of sentences.