The semicolon is probably the most sophisticated punctuation device and is, therefore, well worth adding to your repertoire. First, however, we need to establish the difference between a colon and a semicolon. As you might imagine, it is sometimes the case that in attempting to use one of these devices students opt for the wrong one.
The colon
We can dispose of the colon fairly quickly. Whereas a semicolon is like a heavy-duty comma or surrogate full stop, a colon has a narrower role in Introducing a clause or word or list that amplifies, interprets, explains or reveals what has gone before. The context in which you are most likely to encounter it, and want to use it, is essentially as a substitute for the words ‘us follows’ or ‘that is’. For example:
Dickens wrote two semi-autobiographical novels: David Copperfield and Great Expectations.
The new team of four has just been announced: Short, Parker, Abbott and Cosgrove.
It is also used in the manner that we used it a couple of lines above, to introduce an indented quotation when you are writing, and also to introduce a quotation when the sentence that has preceded it can stand alone. In some ‘Contexts, where the sense continues, a comma precedes the quotation:
When Hamlet says, To be, or not to be .. we know that he is pondering some great question.
But if the sentence has been completed and can stand alone, a colon is used:
Everyone knows Hamlet’s famous soliloquy: ‘To be, or not to be …’.
These two uses of the colon are, in fact, the really straightforward ones. The first we can sum up as introducing a list of items, while the second introduces quoted material, as a stronger alternative to the comma.
Other uses of the colon have in common the idea of being an anticipatory effect, leading from what precedes to what follows. We can see it when there is a following on from one clause to another:
I just want you to be aware of this: one false move and you’re dead.
It helps you gain control of the idea of the colon if you see it very specifically’ as a device that moves meaning forward. In a way it is a dramatic highlighting: a statement is made, and then what follows explains or elaborates on it; or thinks in terms of a simple split: the first part of the sentence makes the general point while what follows the colon is more particular or specific. Notice, however, that the colon is not followed by a dash (not thus:-, but thus:). Notice, too, the spacing: the space comes after the colon, not before! Or both sides of it.