Think of semicolons as sentence splicers.
Semicolons Versus Commas
Also, one important thing to remember is that you never use semicolons with coordinating conjunctions such as and, or, and but when you're joining two main clauses. Instead, if you're joining two main clauses with a coordinating conjunction, you use a comma. For example, "It was zero, and Squiggly wondered if he would freeze to death.”
I don't want to confuse you, but there is one situation where you use semicolons with coordinating conjunctions, and that's when you are writing a list of items and commas just don't do the job of separating them all. Here's an example: "This week's book winners are Herbie in Milligan College, Tennessee; Matt in Irvine, California; and Jan in Oklahoma City, Oklahoma." Those are the real winners in this week's special Scott Sigler book giveaway, and they've each won a copy of his novel Earthcore, but the list also provides a great example of using semicolons in a list. 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.
Finally, you use a semicolon when you use a conjunctive adverb 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, “The aardvark is on vacation; therefore, Squiggly has to carry the weight in this episode.” (The comma after the conjunctive adverb is optional.)
Sometimes people seem frustrated because they have to remember to use commas with coordinating conjunctions and semicolons with conjunctive adverbs, so 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 punctuation mark, small words. Semicolons are bigger and they go with conjunctive adverbs, which are almost always longer than three letters—bigger punctuation, bigger words. I'll put a list of the two kinds of connectors at the bottom of this transcript.
1. Wikipedia contributors. "Conjunctive Adverb," Wikipedia, The Free Encyclopedia, en.wikipedia.org/w/index.php?title=Conjunctive_adverb&oldid=108619955 (accessed February 23, 2007).
|Common Coordinating Conjunctions||Common Conjunctive Adverbs|
|Use these with commas to join main clauses||Use these with semicolons to join main clauses|