Using Semicolons

The semicolon is a hugely powerful punctuation mark. Getting it right will not only impress your tutors and future employers, it will allow you to express your ideas and opinions with more subtlety and precision than ever before. The good news is that it is simple and easy to use and should take you no more than a few minutes to master.

In complicated lists.
The semicolon can be used to sort out a complicated list containing many items, many of which themselves contain commas.

Have a look at this example:

In the meeting today we have Professor Wilson, University of Barnsley, Dr Watson, University of Barrow in Furness, Colonel Custard, Metropolitan Police and Dr Mable Syrup, Genius General, University of Otago, New Zealand.

In a situation such as this, only the mighty semicolon can unravel the mess.

In the meeting today we have Professor Wilson, University of Barnsley; Dr Watson, University of Barrow in Furness; Colonel Custard, Metropolitan Police and Dr Mable Syrup, Genius General, University of Otago, New Zealand.

In most lists a comma is enough to separate the items. In a complicated list like the one above, it is perfectly acceptable to use the semicolon to make the list more understandable.

Separating closely-related independent clauses. 
The semicolon is also used to connect two closely-related independent clauses. Have a look at this example:

• Terry always slept with the light on; he was afraid of the dark. 

The two clauses here are closely connected but the link has not been made explicit. They could have been separated by a full stop.

• Terry always slept with the light on. He was afraid of the dark. 

They could have been connected by a conjunction.

• Terry always slept with the light on because he was afraid of the dark. 
• Terry always slept with the light on, as he was afraid of the dark. 

In this instance we have changed the second clause into a dependent clause; it is directly dependent on the first clause.

If you are going to use a semicolon to connect two clauses, it is very important that the two clauses are both independent. That means that each clause has to be able to stand alone and make complete sense without the other. If either one cannot stand alone, a semi-colon cannot be used.

Style.
Using the semicolon to separate the two clauses has allowed us to imply the relationship between the two without stating it explicitly. This can be quite a powerful tool in allowing/encouraging your reader to make implicit connections. As the reader is involved in the development of the idea, it may well be more persuasive than simply stating the causal relationship between the two clauses. The decision as to whether to use a semicolon or to make the two clauses into separate sentences is one of style and, as such, is up to you the writer. As with many punctuation marks, the semicolon is powerful and can give your writing a good deal more style and precision, but it should not be over used.

Taken from HERE.