A colon is a type of punctuation that is used to precede a list or to separate an explanation or rule from a preceding clause. Colons focus the reader on what follows it and it is important to remember not to use the colon to separate a subject from its verb or object. Also, colons should not separate a preposition from its object.
Alright, now we're talking about an often misunderstood punctuation mark, the lonely Mr. Colon and that's the one with the two dots over each other. And what a colon is, is it's something that you use after independent clauses that precedes a list. It also is something you can use to separate an explanation or a rule from the preceding clause in front of it. You can also use it in conventions like, when you're writing 5:00 o'clock, 5:00 to say that. so that's the three different ways that you use it, but there are some tricks that go along with colons; some things to remember. The number one thing is that a colon focuses attention on what's coming next and that's a nice way to think of when you should use it, when you shouldn't use it. I would advise using colons sparingly, they are effective but you don't want to have one in every other sentence in your paper. The other thing to know about colons and this really helps guide the appropriate placement is you never want to use a colon to separate a subject from it's verb, a verb from it's object or a preposition from it's object. So if you're unsure about if you've placed a colon in the correct place, make sure you go back and double check these three instances to make sure you haven't done one of these. So let's take a look over here and see if we can find the appropriate place to throw the colons in these three examples. so the first one I have is "I love cooking dinners, spaghettis, stir fry, you name it." Now we said a colon can be used at the end of a clause to introduce a list and we've got a list of spaghetti, stir fry and you name it. So what we can do here is instead of a comma which theoretically makes us to run on sentence, we can throw in a colon. 'I love making dinners:' it's going to draw our attention to what's coming next and we've got the list: spaghetti, stir fry, you name it. Alright, the next example. When I grow up I'd like to be a doctor, lawyer or a teacher. So now we've got a list here and I know our inclination and say "we've got a list, let's throw our colon here at the end." But if we put a colon here, I want 'When I grow up I'd like to be: a doctor, a lawyer or a teacher'. We're committing this cardinal sin. We're splitting up a verb from it's object. So we don't want to throw it in there. This was actually a trick one, there's no colon needed here. So you always want to make sure and especially after a 'to be' verb no colon is needed, alright. Finally don't forget our most important rule, be nice. So that other rule about colons is that we can use them to introduce a rule or an exception. We've got a rule here. Don't forget our most important rule. Again we're going to draw our attention to the end because that's the crucial meaning of the sentence. Throw a colon after 'rule' and then people will focus in on that. So now you know the simple easy way to use colons. Hopefully it's not so lonely, you can get it into your writing but remember to use it sparingly.