Good morning, this is a repost from iWriteNetwork. It is a post by Tristi Pinkston and has given me permission to repost it. Thanks Tristi!!
A semi-colon is used to hook together two complete sentences that are closely related. For example:
Today I'm going to sleep in; playing video games all night wasn't a good idea.
Notice that we have a complete sentence before the semi-colon and another complete sentence after the semi-colon. Then notice that they are related. I played video games all night and so I'm going to sleep in - there's a cause and effect here, a definite connection.
Authors get into trouble with the semi-colon in two ways.
First, they try to stick an incomplete sentence there.
Today I'm going to sleep in; dumb video games.
"Dumb video games" isn't a complete sentence. You'd want to use an em-dash here rather than the semi-colon.
The second way to get in trouble is to hook sentences together that really aren't related.
Mark says we need to buy a new car; the kids will be home from school soon.
Okay, that was a super over-the-top example, but you get what I'm saying. If the first sentence and the second sentence aren't directly related, like a cause-and-effect thing or if the second sentence doesn't clarify or enrich the first, etc., they shouldn't be stuck together with a semi-colon.
Semi-colons were used more frequently fifty and a hundred years ago than they are now, but that doesn't mean we should never use them at all. We should use them; they're awesome. (See - like that.) But we should know how to do it correctly so we can be awesome too.