The semicolon (;) is a bit of a puzzle to many writers. Part of the confusion stems from this punctuation mark’s being used incorrectly in a great deal of published material. To clarify, a semicolon is most commonly—and correctly—used in two situations:

1. to separate two independent clauses that seem too closely related to belong in separate sentences, as in,

◊ The company is right to feel good as the quarter comes to a close; financial disclosures show record profits.

2. in a list of items, at least one of which has its own commas, such as,

◊ We’ll take the following items: my mother, whose knowledge of the countryside is unsurpassed; a good map in case we lose battery power for the GPS; plenty of water; and a large, sturdy box to store what we find.

Note: In #1 above, the semicolon is not the only choice for joining the clauses. As indicated in the articles discussing Commas Splices and Run-on Sentences, the writer could have inserted a period instead and created two complete sentences. Another option is to insert a comma and a conjunction.

Whether or not to use a semicolon in cases such as these is something of a judgment call: Just how closely related are the ideas expressed in the two clauses? Are they too closely related to belong in separate sentences but unrelated in ways that call for a conjunction? If so, a semicolon is probably the right choice. After all, doesn’t a semicolon look like a combination of a period and a comma? Its proper use falls somewhere in between.

A Common Error — Do not use a semicolon to separate dependent clauses from independent clauses, or sentence elements that could stand alone as complete sentences. The following is incorrect:

◊ Although we are wary of their dismal track record in electronic commerce; we are going to enter into a limited partnership with them anyway.

A correction to the above sentence would substitute a comma for the semicolon (see the article discussing Commas):

◊ Although we are wary of their track record in electronic commerce, we are going to enter into a limited partnership with them anyway.

More Sentence-level Writing
Varsity Sentence Practice — Appositives
Quick tip about citing sources in MLA style
Who vs. Whom