Colon (:)

How to read it

Unicode encodes it as U+003A COLON and notes that it is also used for division or scale, where the separate RATIO sign ∶ (U+2236) is preferred in mathematics, and that in Finnish and Swedish it marks an abbreviation inside a word. The American Heritage Dictionary defines it as the mark after a word introducing a quotation, explanation, example or series, and after the salutation of a business letter, and as the sign between numbers in times and ratios. The Guardian’s style guide puts it between two parts of a sentence “where the first introduces a proposition that is resolved by the second”, and uses a colon rather than a comma to introduce a quotation that could be a sentence on its own: He said: “You’ll never take me alive.” The US Government Publishing Office’s Style Manual lists more jobs: clock time, Biblical and other citations, between place of publication and publisher in a bibliography, between title and subtitle, and in proportions.

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Colon or semicolon?

The colon introduces; the Semicolon (;) joins two clauses that are closely related and could each stand alone (American Heritage Dictionary). The Guardian’s style guide warns that the distinction is being lost and that the two “are not” interchangeable. Its example of a semicolon “where only a colon will do” is one of its own sentences from 2010: “Here’s a task for the new coalition government; set up a Drumming Taskforce today, and appoint a Snare Tsar.”

A capital letter after it?

Style guides differ. Chicago lowercases the first word after a colon inside a sentence, even when a full sentence follows, but capitalizes it when the colon introduces quoted speech or two or more sentences (CMOS Shop Talk). The Guardian usually lowercases after a colon in a headline (“Osborne: there is no plan B”), except after the name of a series or a tag such as “Exclusive”.

Times, ratios and Bible verses

Cambridge Dictionary says British English writes times with a full stop or a colon (9.30 or 9:30); the American Heritage Dictionary’s example is 2:30 AM. GOV.UK writes ratios with no space either side, 5:12, and the GPO Style Manual writes a ratio of proportion with a double colon. Unicode notes that the colon is also used for division, a job it shares with the division sign.

Look-alikes

Unicode separates the colon from the ratio sign ∶ (U+2236), the modifier letter triangular colon ː (U+02D0), the Armenian full stop ։ (U+0589), the Hebrew sof pasuq ׃ (U+05C3) and the two dot punctuation ⁚ (U+205A). The tricolon ⁝ (U+205D) has three dots.