Semicolons

Rule 1a. A semicolon can replace a period if the writer wishes to narrow the gap between two closely linked sentences (independent clauses).

Examples:
Call me tomorrow; you can give me an answer then.
We have paid our dues; we expect all the privileges listed in the contract.

Rule 1b. Avoid a semicolon when a dependent clause comes before an independent clause.

Incorrect: Although they tried; they failed.
Correct: Although they tried, they failed.

Rule 2. Use a semicolon before such words and terms as namely, however, therefore, that is, i.e., for example, e.g., for instance, etc., when they introduce a complete sentence. It is also preferable to use a comma after these words and terms.

Example: Bring any two items; however, sleeping bags and tents are in short supply.

Rule 3. Use a semicolon to separate units of a series when one or more of the units contain commas.

Incorrect: The conference has people who have come from Moscow, Idaho, Springfield, California, Alamo, Tennessee, and other places as well.

Note that with only commas, that sentence is hopeless.

Correct: The conference has people who have come from Moscow, Idaho; Springfield, California; Alamo, Tennessee; and other places as well.

Note that a semicolon, rather than a comma, after Tennessee is correct because and other places as well also constitutes a unit of the series.

Correct: Dante Martinez, a registered nurse; Susan Brooks, a dietician; and Chien-Ling Ko, a physical therapist, attended the meeting.

In this case, attended the meeting is not a unit of the series and therefore is preceded only by a comma.

Rule 4. A semicolon may be used between independent clauses joined by a connector, such as and, but, or, nor, etc., when one or more commas appear in the first clause.

Example: When I finish here, and I will soon, I'll be glad to help you; and that is a promise I will keep.

Rule 5. Do not capitalize ordinary words after a semicolon.

Incorrect: I am here; You are over there.
Correct: I am here; you are over there.