Comma Queen discusses the semicolon; or mastering the giant comma

Traditionally, the semicolon has three uses: it can replace a comma in a series that includes interior commas, such as this one; it can replace a comma and a conjunction in a compound sentence, creating a subtle relationship between clauses; and it can be used artfully to suggest hesitations and inflections, a dangerous practice best explored in a graduate seminar on Henry James.

In Episode 9 of Comma Queen, Mary Norris explains why the proper use of the semicolon is the hallmark of literacy.