Grammar Girl here. Surprise! You get a bonus show today because Thursday is National Punctuation Day and I'm going to have a slightly different kind of podcast to celebrate.

Today's topic is semicolons.

But first, did you know that you can get a free trial membership and a free audiobook by signing up for Audible at audiblepodcast.com/gg. It's a great deal for Grammar Girl listeners from our sponsor.

I get a lot of questions about semicolons, so it's time to clear up some confusion.

Semicolons Separate Clauses

Semicolons separate things. Most commonly, they separate two main clauses that are closely related to each other but could stand on their own as sentences if you wanted them to

Here's an example:

I have a big test tomorrow; I can't go out tonight.

The two clauses in that sentence are separated by a semicolon and could be sentences on their own if you put a period between them instead:

I have a big test tomorrow. I can't go out tonight.

Semicolons Create Variety

One reason you might choose to use a semicolon instead of a period is if you wanted to add variety to your sentence structure; for example, you might use a semicolon if you thought you had too many short, choppy sentences in a row.

Semicolons Emphasize Relatedness

Another reason to use a semicolon is to draw attention to how related your two clauses are. The semicolon in our example sentence highlights that the reason you can't go out tonight is that you have a big test tomorrow. You wouldn't write, “English is my fifth period class; I can't go out tonight,” because those two main clauses have nothing to do with each other. I can't think of a single reason why English being fifth period would mean you can't go out tonight.

Semicolons and Coordinating Conjunctions

You should never use a semicolon and a coordinating conjunction such as “and,” “so,” and “but” to join two main clauses; that's the job of a comma. If you want to use a coordinating conjunction you'd write it like this:

I have a big test tomorrow, so I can't go out tonight.

Nevertheless, there are a couple of instances where it's OK to use a semicolon with a coordinating conjunction.

Semicolons Can Join Complex Clauses with a Coordinating Conjunction

First, if you have a long sentence with multiple independent clauses, and some of those clauses contain internal punctuation such as a comma, you can use a semicolon with a coordinating conjunction to make the separation between clauses more clear. Here's an example:

If you want me to go out tonight, you need to help me with my homework first; and if you say no, I'll know that you don't really care about going out.

Because each half of that long sentence has a conditional clause that must contain a comma, it's OK to use a semicolon before the “and” that separates those two parts. You could make them two sentences, but you don't have to; and because they are so closely related, it makes a lot of sense to have them be together separated by the semicolon. The “and” after the semicolon is actually optional in this case, but I think it adds to the flow of the sentence.

Semicolons Can Separate Items in a Complex List

The second instance in which it's OK to use a semicolon with a coordinating conjunction also occurs when you have an excess of commas: it's when you need to separate list elements that contain commas.

Here's an example:

This week's winners are Joe from Reno, Nevada; Diane from Phoenix, Arizona; and Matt from Irvine, California.

Because each item in the list requires a comma to separate the city from the state, you have to use a semicolon to separate the items themselves.

Notice again that both times you can use a semicolon with a coordinating conjunction such as “and,” it's because commas are already being used for something else, so using a comma could be confusing to readers.

Semicolons with Conjunctive Adverbs and Transitional Phrases

Finally, you use a semicolon when you use a conjunctive adverb or transitional phrase to join two main clauses.

Conjunctive adverbs are words such as “however,” “therefore,” and “indeed,” and they "usually show cause and effect, sequence, contrast, comparison, or other relationships" (1). For example, “I have a big test tomorrow; therefore, I can't go out tonight.” (The comma after the conjunctive adverb is optional.)

A transitional phrase is something like “for example” or “in other words.” A sentence with a transitional phrase could read as follows:

I have a big test tomorrow; as a result, I can't go out tonight.

Coordinating Conjunctions Versus Conjunctive Adverbs

Sometimes people seem frustrated because they have to remember to use commas with coordinating conjunctions and semicolons with conjunctive adverbs most of the time. If you can't keep the difference straight in your head, it can help to remember that commas are smaller than semicolons and go with coordinating conjunctions, which are almost always short two- or three-letter words—small words, small punctuation mark.

Semicolons are bigger and they go with conjunctive adverbs and transitional phrases, which are almost always longer than three letters—bigger words, bigger punctuation. I'll put a list of the different kinds of connectors on the website.

Audible

A few weeks ago I recommended Stephen King's audiobook “On Writing,” and after that a listener named Tally, who also liked “On Writing,” recommended another book called “On Writing Well” by William Zinnser. She said it's a really good audiobook that she listened to on cassette years ago, and now it's available at Audible. So you can get “On Writing” or “On Writing Well” as your free audiobook when you sign up for a new account at audiblepodcast.com/gg. You get a free two-week trial and a free audiobook to keep forever. That's audiblepodcast.com/gg.

The Grammar Devotional

Also, my new book, The Grammar Devotional, is coming out in three weeks. If you want the most up-to-date information about my book tour and where you can get a signed book, it's a good idea to follow me on Twitter or Facebook or sign up for my free grammar tip e-mail newsletter. I'm @grammargirl at Twitter and my Facebook page is facebook.com/GrammarGirl, and you can sign up for the newsletter in the Grammar Girl section of quickanddirtytips.com. We'll also be doing a lot of giveaways to promote the book in the next few weeks on Twitter and in the newsletter, so it's a good time to sign-up.

That's all. Thanks for listening.

References

1. Wikipedia contributors. "Conjunctive Adverb," Wikipedia, The Free Encyclopedia, en.wikipedia.org/w/index.php?title=Conjunctive_adverb&oldid=108619955 (accessed February 23, 2007).