Colons shouldn't be confusing. Just think of them as a really nifty way of pointing your reader towards a bit of relevant information. As with all the articles in the ‘Punctuation Pointers’ blog series, we’re keeping it short, sweet and uncomplicated with the essential do's and don'ts of correct colon use.
1. Do use a colon to introduce a subtitle after a title. It's up to you whether you start the subtitle with a capital letter or not. I've opted for not in this blog post because I thought the aesthetic of two lower case d's looked better, but it's just a question of personal style choice.
2. Do use a colon to introduce a list.
E.g. The cake ingredients include the following: flour, butter, eggs, cocoa powder and sugar.
3. Do use a colon instead of a linking word or phrase (e.g. namely, such as, that is …) to join two statements where the second explains the first.
E.g. I have two dogs: Lucy and Benoit.
However, there’s no need for both a colon and a linking word, i.e. I have two dogs namely: Lucy and Benoit. It's one or the other.
(I don't actually have two dogs called Lucy and Benoit, but if I did those names are right at the top of my potential puppy list!).
4. Do use a colon to introduce direct speech or quote.
E.g. In the words of Charles Dickens: “It was the best of times, it was the worst of times.”
Alternatively, you can use a comma.
5. Don't follow a colon with a dash (:−). This was once quite common, but in modern writing it's seen as outdated so best avoided (unless you just fancy going a bit retro with your punctuation practice).
6. (UK WRITERS) Don't follow a colon with a capital letter unless it's part of a title (see Do's No. 1). In the US, following a colon with a capital letter is completely acceptable. In fact, it's actively encouraged if it precedes a complete sentence. This is just one example where US and UK English differ in their language style preferences. You can find out more about this in one of my first blog posts here.
New Hart’s Rules: The Oxford Style Guide, 2nd ed. (2014) Oxford: Oxford University Press
Seely, J. (2013) Oxford A−Z of Grammar and Punctuation (2nd ed.) Oxford: Oxford University Press