"Hey, don't forget me," says the semi-colon.

A colon - as previously described - is used 1) to connect a definition to an independent clause, 2) to start a list, 3) following a formal salutation, and 4) to connect an independent clause to a direct quotation.

But what about the colon's little brother - or perhaps more social cousin - the semi-colon?

First, a semi-colon is used to connect two independent clauses (complete sentences) that are related to one another. In this situation, you could also use a period but would elect to use a semi-colon if the two independent clauses relate or interact with one another.

1. It was a dark and stormy night; our hero put on a raincoat. (correct)
2. It was a dark and stormy night. Our hero put on a raincoat. (also correct)

Here both examples are correct and mean basically the same thing. The use of a semi-colon (sentence 1) indicates that there is a direct relationship between the weather and the action of the hero.

3. It was a dark and stormy night: our hero put on a raincoat. (incorrect)
4. It was a dark and stormy night: by 4:00 AM over three inches of rain had fallen. (correct)

Here we are getting into the subtle difference between a colon and semi-colon. In sentence 3, the second independent clause does not define the first. Thus, the colon is incorrect. In sentence 4, however, the second clause does define the first. Thus, the colon is correct.

Second, a semi-colon is used to connect two independent clauses when using "however," "therefore," "furthermore," or "thus" (conjunctive verbs). Once again, it is also correct to use a period. Whether we use a period or a semi-colon, the use of the conjunctive verb already indicates that there is a relationship between the two independent clauses. Thus, in this instance, the only reason to use a semi-colon as opposed to a period is to add variety to your sentence structure. In other words, it is a matter of style, not grammar.

5. Cement is very expensive; therefore, it is cheaper to build a house with wood. (correct)
6. Cement is very expensive. Therefore, it is cheaper to build a house with wood. (correct)

Here is a tricky point. If you are connecting two independent clauses with "and" or "but" (coordinating clauses), then you cannot use a semi-colon (sentence 7). In this case, you need to either remove the coordinating clause (sentence 8) or use a comma (sentence 9).

7. Cement is very expensive; but it is cheaper to build a house with wood. (incorrect)
8. Cement is very expensive; it is cheaper to build a house with wood. (correct)
9. Cement is very expensive, but it is cheaper to build a house with wood. (correct)

Third, a semi-colon is used to add clarity to a list that already has commas (sentence 10). In this case, the semi-colon brings order to an otherwise confusing sentence.

10. At the grocery store, Victor bought everything he needed to make dinner: a round steak, which he plans to use as a roast; frozen mixed vegetables; and bakery-fresh brownies, his daughter's favorite dessert. (correct)
11. At the grocery store, Victor bought everything he needed to make dinner: a round steak, which he plans to use as a roast, frozen mixed vegetables, and bakery-fresh brownies, his daughter's favorite dessert. (incorrect and confusing)
12. At the grocery store, Victory bought everything he needed for dinner: a round steak, mixed vegetables, and brownies. (correct)

Note that in a simple list (sentence 12), a comma will suffice. Think of the semi-colon as the Sheriff of a sentence with a list that only needs to intervene when a comma fails to bring order and clarity to the sentence.