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4 Punctuation

4.5 Colon

The colon points forward: from a premise to a conclusion, from a cause to an effect, from an introduction to a main point, from a general statement to an example. It fulfils the same function as words such as namely, that is, as, for example, for instance, because, as follows, and therefore. Material following a colon need not contain a verb or be able to stand alone as a sentence:

  • That is the secret of my extraordinary life: always do the unexpected

  • It is available in two colours: pink and blue

Use the colon to introduce a list; formerly a colon followed by a dash : — was common practice, but now this style should be avoided unless you are reproducing antique or foreign-language typography:

  • We are going to need the following: flashlight, glass cutter, skeleton key, …

  • She outlined the lives of three composers: Mozart, Beethoven, and Schubert

The word following a colon is not capitalized in British English (unless it is a proper name, of course), but in US English it is often capitalized if it introduces a grammatically complete sentence:

Mr Smith had committed two sins: First, his publication consisted principally of articles reprinted from the London Review

A colon should not precede linking words or phrases in the introduction to a list, and should follow them only where they are introduced by a main clause:

  • She outlined the lives of three composers, namely, Mozart, Beethoven, and Schubert

  • She gave this example: Mozart was chronically short of money

Do not use a colon to introduce a statement or a list that completes the sentence formed by the introduction:
  • Other Victorian authors worth studying include Thackeray, Trollope, and Dickens

A dash can also be used in a similar way to a colon, but they are not interchangeable: a dash tends to be more informal, and to imply an afterthought or aside (see 4.11.2).

A colon is used after the title of a work to introduce the subtitle. It may be followed by a capital or a lower-case letter (Oxford style uses a capital):

  • Finding Moonshine: A Mathematician’s Journey through Symmetry

  • Monster: The Autobiography of an L.A. Gang Member

A colon may introduce direct speech: see 9.2.2.

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