Colon (punctuation)

A colon is a mark consisting of two points arranged vertically (:). As a punctuation mark it is used in many languages. It is also used in mathematics to show ratios: a ratio of five to four can be written 5:4.

Punctuation mark

Like a full-stop (BrE, known as a period in AmE), a colon can follow a grammatically complete utterance. The same is true of the semi-colon. (In the case of the full stop/period the complete phrase is called a sentence.)

Unlike the full-stop and semi-colon, which merely mark an ending, a colon points forward, 'delivering' what is promised before it:

I have something to tell you: you were right after all.