The semi-colon (;) has only one major use. It is used to join two complete sentences into a single written sentence when all of the following conditions are met:

1. The two sentences are felt to be too closely related to be separated by a full stop;

2. There is no connecting word which would require a comma, such as ‘and’ or ‘but’;

3. The special conditions requiring a colon are absent.

Here is a famous example:
‘It was the best of times; it was the worst of times.’

A semi colon can always, in principle, be replaced by either a full stop (yielding two seprate sentences) or by the word ‘and’.”

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Thanks Penguin. There is also a semi-colon usage for lists, which is also happens to be demonstrated above.

Meredith