How to Use Semicolons
This description is modified from the entry in Jack Lynch's Guide to Grammar.
Semicolons probably produce more confusion and misery than all the other punctuation marks combined. But they're really not very difficult to master.
The semicolon has only two common uses. The most important is to separate two independent clauses in one sentence: "Shakespeare's comedies seem natural; his tragedies seem forced." Here's how to tell whether this one is appropriate: if you can use a period and begin a new sentence, you can use a semicolon. In other words, this kind of semicolon can always be replaced by a period and a capital letter. In the example, "Shakespeare's comedies seem natural. His tragedies seem forced" is correct, so a semicolon can be used. (If you used a comma here — "Shakespeare's comedies seem natural, his tragedies seem forced" — you'd be committing the sin of comma splice.) Make sure you do not use a semicolon as a colon.
The semicolon is also sometimes used to separate items in a list. In general, you should avoid this, unless the items in the list themselves contain commas. Take, for example, the following items:
These should be listed with commas as "peanuts, popcorn, and crackerjacks".
Not consider these items:
Semicolons could be used to separate these items in order to avoid any confusion based on the commas in the items. So you might write out the list as "the Odyssey, through book 12; Ovid's Metamorphoses, except for the passages on last week's quiz; and the selections from Chaucer."