A colon means “that is to say” or “here’s what I mean.” Colons and semicolons should never be used interchangeably. They can add sophistication to your written work.
There are two main rules that you should know:
- Use a colon to introduce an item or a series of items. Do not capitalize the first item after the colon (unless it’s a proper noun).
You know what needs to be done: practise.
You may be required to bring many things: sleeping bags, pans, utensils, and warm clothing.
I want the following items: butter, sugar, and flour.
Avoid using a colon before a list if it directly follows a verb or preposition that would ordinarily need no punctuation in that sentence.
I want: butter, sugar, and flour.
Recommended: I want butter, sugar, and flour.
Here is what I want: butter, sugar, and flour.
2. A colon instead of a semicolon may be used to join an independent clause (a clause that makes sense on its own) to a word, phrase or clause with the idea that the second element is to explain, expand or illustrate the idea of first clause.
He became a vet: he couldn’t stand to see animals suffer.
He set up an animal clinic: there were none in his city.
He got what he worked for: he really earned that promotion.
Here’s a handy video explaining the colon:
More examples and quizzes to be found at: http://www.grammarbook.com/punctuation/colons.asp