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“Many students avoid colons and semicolons altogether because they do not know how to use them ... [but] these punctuations marks are graceful, helping authors to write with style.”
Colons can easily be misused but if used properly can be very helpful in your writing. They have a range of uses; the two main ones are explained below.
To introduce a list
The problem is that not all lists need to be introduced by a colon. What you need to remember is that the clause (group of words containing a verb) that comes before the colon must make sense on its own.
Compare the two sentences below.
Students are expected to carry out a range of activities: attend lectures, take part in tutorials, produce written work, meet deadlines for assignments and sit examinations.
Students are expected to arrive on time for classes and lectures, to work independently, to keep appointments, to be considerate to others and to the environment.
In the first sentence, “Students are expected to carry out a range of activities” makes perfect sense. It is therefore correct to use a colon before the list.
In the second one, “Students are expected to” does not make sense on its own. Something is clearly missing. This means that no colon is needed and it would be incorrect to use one before the list.
So, if you have a list, remember you only use a colon before it if the list follows a clause that could be used on its own.
To introduce the second half of a sentence when it explains/expands on the first half
It can be seen as an invitation for the reader to continue reading about an idea. Think of it as meaning "let me explain..." or "what I mean by that is..."
In the sentence below, the main idea is that the British diet is often not as healthy as it should be. After the colon, the reader finds an explanation of why this is the case.
The average British diet is often considered unhealthy: it tends to contain too many fried foods, too many ready prepared foods with a high salt content and not enough fresh vegetables.
As in the case of the list (see above) the words before the colon make sense on their own (they are a main clause). What follows the colon is additional information. If the first part of the sentence cannot be used alone, do not use a colon.
Capital letter after or not?
One minor complication is the question of whether or not to use a capital letter to start the word following the colon. If the explanation after the colon contains more than a single sentence you should use a capital.
Mediterranean cookery is considered healthy: It uses olive oil, fresh vegetables and fish. It often also includes a moderate amount of wine and avoids the use of butter.
If the words following the colon are a quotation, again a capital letter needs to be used for the first word after the colon.
The advice given by the Skills Team on research proposals aims to be reassuring: “Writing a research proposal is like any other form of writing.”
In other cases, the best advice is probably to be consistent. Either always use a capital or always use a lower case letter after the colon. If in doubt, you could perhaps check whether your tutor has a strong preference and be guided accordingly!
You’ll be pleased to learn that semi-colons are both extremely useful and easy to use!
In complicated lists
Some lists are complicated and using semi-colons makes them much easier for the reader to understand. (Always remembering to help your reader is so important.) Generally a comma is sufficient to separate items in a list but in lists like the one below commas are not enough.
When she conducted her research she travelled to Selby, Yorkshire, Peterborough, Lincolnshire, Newcastle, Northumbria, Carlisle, Cumbria and Buxton, Derbyshire.
Adding semi-colons makes the following sentence much easier to read and understand:
When she conducted her research she travelled to Selby, Yorkshire; Peterborough, Lincolnshire; Newcastle, Northumbria; Carlisle, Cumbria and Buxton, Derbyshire.
To link two closely-related clauses
Semi-colons can be used to link two clauses (groups of words with a verb) which could stand on their own. Consider the following two sentences:
I always park in the Salmon Grove car-park. It’s not far from my office.
In this case there are two, separate sentences and although grammatically correct, the punctuation does not help the reader see the relationship between the two. When such a close link is implicit, you can use a semi-colon to separate them instead:
I always park in the Salmon Grove car-park; it’s not far from my office.
It would also be possible to link the two sentences with a conjunction or “joining-word”. In this case, there is no semi-colon:
I always park in the Salmon Grove car-park because it’s not far from my office.
I always park in the Salmon Grove car-park since it’s not far from my office.
When using a semi-colon to connect two clauses, remember that each clause has to make sense on its own. If it does not, do not use a semi-colon.
Using a semi-colon is a good way to avoiding using the comma-splice.