Editorial Style Guide
General Style Preferences: Punctuation
Semicolons and Colons
Use semicolons to indicate a greater break of thought than that indicated by a comma, but less than that indicated by a period.
Use semicolons to separate items in a series when the items are long or require commas within an item: The committee members include two representatives of the School of the Arts, one from dance and one from music; two representatives of the School of Liberal Arts and Sciences, one from the humanities and one from the sciences; and two members of the administration, the provost and the registrar. Note that a semicolon is used before the final and in such a series.
Use a semicolon to link independent clauses when a conjunction such as and, but, or for is not present: We expected rain; it snowed. In most cases, it will be best to separate these independent clauses into two sentences.
A colon is used most frequently at the end of a sentence or phrase to introduce a list. It should generally convey the sense of “as follows.” In running text, capitalize the first word following the colon only if it is a proper noun or the beginning of a complete sentence: Columbus used three ships on his first voyage toward the Indies in 1492: the Niña, the Pinta, and the Santa Maria. They faced a dilemma: Should they stay in New Orleans and help their neighbors, or should they move to Atlanta? Colons are also used to introduce a subtitle (Freedom and Equality: A History), for emphasis (He had one love: chess), and in dialogue and Q&A interviews.