The primary use of a semi-colon is to link two sentences together.
Now, obviously, sentences are usually kept separate and distinct. Sometimes, however, they are very involved with each other, and like to keep close. Like twins, or mirror images, they’re more connected to each other than to the sentences next door. Usher in the semi-colon.
- My mother was a terrible cook; we ate out a lot.
- Cable television is expensive; renting movies is cheap.
It is important to remember, however, that the sentences connected by the semi-colon be complete sentences, and if you’re using a conjunction (and, but, or), you don’t need the semi-colon. Like, for example, that last sentence. I could have stopped after “complete sentences,” added a period, and then started up the next sentence with “If you’re using.” I could also have put a semi-colon there and dropped the “and.” It’s your choice. As a writer, you have options, but like at certain restaurants, no substitutions are allowed.
Semi-colons can also be used to break apart the items in a series, when a comma isn’t quite enough to do the job.
Usually, when writing a list, you use commas to keep items separate. (“My favorite ice cream flavors are vanilla, peppermint, and pistachio.”) When the items start getting more complicated, though, commas can become unclear. (“I have travelled to Boston, Massachusetts, Madison, Wisconsin, and San Franciso, California.”) This is where the semi-colon comes into its own.
- I have travelled to Boston, Massachusetts; Madison, Wisconsin; and San Francisco, California.
- My dogs’ ages are Katy, 9; Chappy, 7.
And, that’s it. Clear? Unclear? Anything I left confused? Further questions?