This sentence contains a list of four animals. The first part of the sentence tells you that there will be four animals; then the colon tells you "here are the four animals".
You can also use a colon to introduce an explanation or a definition of something. For instance:
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The colon (:) seems to bewilder many people, though it's really rather easy to use correctly, since it has only one major use. But first please note the following: the colon is never preceded by a white space; it is always followed by a single white space in normal use, and it is never, never, never followed by a hyphen or a dash ‹ in spite of what you might have been taught in school. One of the commonest of all punctuation mistakes is following a colon with a completely pointless hyphen.
The colon is used to indicate that what follows it is an explanation or elaboration of what precedes it. That is, having introduced some topic in more general terms, you can use a colon and go on to explain that same topic in more specific terms. Schematically:
More general: more specific
A colon is nearly always preceded by a complete sentence; what follows the colon may or may not be a complete sentence, and it may be a mere list or even a single word. A colon is not normally followed by a capital letter in British usage, though American usage often prefers to use a capital. Here are some examples:
[Explains what the clear situation is.]
[Identifies the one thing she was sure of.]
[Explicates the golden rule.]
[Identifies the friends in question.]
[Explains why we found it easily.]
[Identifies the post in question.] Very occasionally, the colon construction is turned round, with the specifics coming first and the general summary afterward:
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You should not use a colon, or any other mark, at the end of a heading which introduces a new section of a document: look at the chapter headings and section headings in the present document.
It is, however, usual to use a colon after a word,phrase or sentence in the middle of a text which introduces some followingmaterial which is set off in the middle of the page. There are three consecutiveexamples of this just above, in the second, third and fourth paragraphs of this section.
The colon has a few minor uses. First, when you cite the name of a book which has both a title and a subtitle, you should separate the two with a colon:
You should do this even though no colon may appear on the cover or the title page of the book itself. Second, the colon is used in citing passages from the Bible:
Observe that, exceptionally, the colon is not followed by a white space in Biblical references. Third, the colon may be used in writing ratios:
In formal writing, however, it is usually preferable to write out ratios in words:
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Finally, the colon is used in formal letters and in citing references to published work.



