Semicolons ∴

Mary Norris, writing for The New Yorker on semicolons, quotes a book titled Punctuation..?:

It is especially good on the difference between the colon and the semicolon. The semicolon is listed last in the Table of Contents, but it makes an eloquent appearance earlier, in the entry for the colon: “A semicolon links two balanced statements; a colon explains or unpacks the statement or information before it.”

That’s a very concise and memorable rule.