From Rick:

As I did with commas, I’m going to cover the basics of semicolons. This is not an exhaustive list of their uses. For the finer points, consult The Chicago Manual of Style.

THE SEMICOLON– Many people misunderstand the semicolon. Some believe it to be a strong comma. That’s not the case. If anything, it’s more like a weak period. And because it functions more like a period, it should not be used to connect phrases and dependent clauses (that is, ones lacking a subject and verb). I see it abused all the time by both new and established writers.

RULE #1: Use the semicolon to indicate a close relation between two independent clauses in place of a conjunction (such as “and” or “or”). The semicolon is used in this case to break up what might otherwise be a long sentence or to join short sentences to keep the narrative from sounding choppy.

Here’s one example.

Jennifer loved living in a museum; what young girl wouldn’t?

For a second example, let’s look at a passage written three ways.

In the past year I had learned to be tolerant, I had learned to counsel, and I had learned when to shut my door–all valuable, real-world skills. [Long and awkward, and not all that interesting]

In the past year I had learned to be tolerant. I had learned to counsel. I had learned when to shut my door. All of these were valuable, real-world skills. [Short, choppy, uninteresting]

In the past year I had learned to be tolerant; I had learned to counsel; I had learned when to shut my door–all valuable, real-world skills. [Smoother and has more punch]

Of course, there are other ways to write this passage, but this use of the semicolon demonstrates another way to vary your sentence structure.

One good test of proper semicolon use is whether you can replace the semicolon with “and.” If you can, chances are you good that you’ve used it properly. But there’s an additinal test. Are the sentences closely related?

Here are some wrong uses of the semicolon:

John still felt he could call her Mrs. Parker; Alice would feel offended at that; she was a friend, after all; treated him as if he was her own kid. [This is wrong on several fronts. For one, it overuses semicolons. Two, most of them cannot be replaced with “and.” Three, the last one is a clause, not a complete sentence. The last semicolon would be better off as a comma.]

Here’s another bad example:

The honking jeep outside my window at eight-thirty a.m. quashed my planned sleep-in; I had not intended to attend my father’s make-Scott-miserable party. I didn’t bother shaving; what should I wear though? I considered scrungy jeans, but they all looked pretty sad. Deciding which pair was the scrungiest was just too tough this early in the morning. Inspiration struck. Cammies! I’d bought them as a personal protest this past year in San Diego so he didn’t know about them; sneakers completed the look. [None of these semicolons connects two closely related sentences. All of them should be periods.

RULE #2: Use a semicolon as a substitute for a comma in a complex series to separate items in a series when the items themselves have commas within them. This is the really the only instance where a semicolon should substitute for a comma in fiction.

NOTE: This is a RARE use of the semicolon and should be employed only when necessary. Don’t force yourself to write sentences that require it.

The furniture in the room consisted of a beat up, early American, cherry desk, a worn, black leather couch, and two broken, cheap, wooden chairs [This is purely an illustration. As you can see, it’s difficult for the eye to parse the sentence with all those commas. Here is where we use semicolons in place of the commas that separate the individual items.]

The furniture in the room consisted of a beat up, early American, cherry desk; a worn, black leather couch; and two broken, cheap, wooden chairs.

Don’t overuse semicolons. As with exclamation marks, colons, and long dashes (em-dashes), they should be used sparingly. If you find yourself using them on every page, you’re likely misusing them, and at the very least you’re overusing them.

Keep in mind that your staples of punctuation are periods and commas (and question marks when required). Don’t resort to the use of semicolons, colons, dashes, and exclamation marks simply because you’re bored with commas and periods or you believe that good writing requires alternatives to these. Every piece of punctuation has a purpose. Stick to the basics until you fully understand the finer points of each piece of punctuation. Use your tools wisely and properly.