The semicolon is a mark of separation that falls somewhere between the comma and the period in impact. Of course, you can’t just use a semicolon as a substitute for either a comma or period whenever you want. I’ll present guidelines for the two main contexts in which the semicolon can be used:
1. Connecting Two Independent Clauses (Sentences)
The most common use of a semicolon is between two sentences, also called main or independent clauses. A main/independent clause is a group of words that include a subject and verb and can stand alone as a sentence because the words express a complete thought. However, these clauses can also just be part of a sentence.
The semicolon can be used to link two sentences/main clauses/independent clauses that are related in meaning and context.
Take these two sentences as an example:
His marketing campaigns have attracted more than 700,000 new customers. His most successful promotion achieved revenue of $8.2 million.
If you use a semicolon to link the two sentences, they become this sentence would become this: His marketing campaigns have attracted more than 700,000 new customers; his most successful promotion achieved revenue of $8.2 million.
According to one of my favorite websites, Guide to Grammar and Writing, using the semicolon in this way also allows the writer to imply a relationship between nicely balanced ideas without actually stating that relationship.
2. Separating a Series of Items That Contain Commas
Although commas are usually used to separate items in a series, when the items themselves include commas, it can become confusing. In those cases, semicolons are the preferred option for separating the items.
If you’re writing a series that consists of long or complicated elements, use a semicolon to separate each element in the series.
Committee members consisted of the following: John Doe, mayor of Anywhere; Jane Doe, Professor of Anthropology; Jack Doe, CEO of Widgets, Inc.; and Cynthia Doe, chairman of the safety commission.
Note: The Associated Press Stylebook calls for the use of the semicolon with the and before the final item.
This covers all the basic information on how to use the semicolon. For more information, check out the “90-Second Semicolon” vidcast series on the Purdue OWL YouTube Channel.