Think of the semicolon [ ; ] as a comma on steroids, a super-comma.
The semicolon has two primary uses:
Join Independent Clauses
A semicolon can join independent clauses together all by itself; it doesn’t need a coordinating conjunction like a comma does.
Do you want a cheeseburger; would you like fries with that?
Betty likes horror movies; Lee preferrs romantic comedies.
Akira drove to Starbucks; he ordered an espresso; he drank it quickly.
(Typically, you use semicolons only to join together closely related sentences.)
Separate Items in a Series Containing Commas
If the items in a list contain internal commas, you need a semicolon to separate the series of lists.
Many European flags simply contain three colored bands: blue, white, and red for France; green, white, and orange for Ireland; black, red, and yellow for Germany; and green, white, and red for Italy.
Fernando works out chest, shoulders, biceps, and quads on Mondays and Thursdays; back, triceps, and hamstrings on Tuesdays and Fridays; abs plus aerobics on all four days; and rests on Wednesdays, Saturdays, and Sundays.
Don’t Confuse the Semicolon and the Colon.
Semicolons join things together. Colons introduce things.
The colon [ : ] comes after a main clause and introduces something relevant to that clause: a list, a quotation, or a phrase predicted in the main clause.
David Foster Wallace wrote three novels: The Boom of the System, Infinite Jest, and The Pale King.
Polonius gives Laertes sage advice: “This above all, to thine own self be true” (1.3.77).
After diner, the president made a shocking announcement: he would resign by the end of the week.