Use a colon after an independent clause to introduce a list of particulars, an appositive, an amplification, or an illustrative quotation.
A colon tells the reader that what follows is closely related to the preceding clause. The colon has more effect than the comma, less power to separate than the semicolon, and more formality than the dash. It usually follows an independent clause and should not separate a verb from its complement or a preposition from its object. The examples in the lefthand column, below, are wrong; they should be rewritten as in the righthand column.
Your dedicated whittler requires:
a knife, a piece of wood, and a back porch.
Understanding is that penetrating quality of knowledge that grows from:
theory, practice, conviction, assertion, error, and humiliation.
Your dedicated whittler requires three props:
Knife, a piece of wood, and a back porch. Understanding is that quality of knowledge that grows from theory, practice,
conviction, assertion, error and humiliation.
Join two independent clauses with a colon if the second interprets or amplifies the first.
But even so, there was a directness and dispatch about animal burial: there was no stopover in the undertaker’s foul parlor, no wreath or spray.
A colon may introduce a quotation that supports or contributes to the preceding clause.
The squalor of the streets reminded her of a line from Oscar Wilde: “We are all in the gutter, but some of us are looking at the stars.”
The colon also has certain functions of form: to follow the salutation of a formal letter, to separate hour from minute in a notation of time, ad to separate the title of a work from its subtitle or a Bible chapter from a verse.
Dear Mr. Montague:
departs at 10:48 P.M.
Practically Calligraphy: An Introduction to Italic Script