Semicolons = Period (SAT & ACT)

I find that a lot of people are afraid of semicolons. Either that, or they sort of kind of think they might have an idea about how to use them... From what I have observed, semicolons are probably the most misunderstood punctuation mark. Which is very unfortunate because they're actually very simple to use. They also show up on the SAT (Fixing Sentences only) and ACT English a whole lot.

Here's the rule:

Semicolon = Period

That's it (well, almost). Seriously. Wherever you can use a period, you can also use a semicolon. If you want to get a tiny bit more technical about it, a semicolon is used to join two independent clauses, but you don't even need to go that far.

There's one more tiny little piece, though: whenever you start a clause with "however" or "therefore," you need to place a semicolon before it, thereby attaching it to the previous sentence. It is 100% incorrect to use a comma, and technically you shouldn't use a period either.

Correct: It's very sunny outside now; however, it might rain later.

Incorrect: It's very sunny outside now, however, I heard it might rain later.

Incorrect: It's very sunny outside now. However, I heard it might rain later.