The semicolon gets no respect; it gets no respect at all.
Imported into English from Italy in the Elizabethan era, the semicolon reached its high-water mark in the mid-18th century when sentences were wont to meander lengthily and majestically to the sea of understanding. The revolt against it began about the time of the American and French Revolutions (coincidence?) and has gathered force ever since. In 1848, Edgar Allen Poe said he was “mortified” that printers used so many semicolons. In 1865, grammarian Justin Brenan gleefully announced, “The semicolon has been gradually disappearing, not only from newspapers, but from books—insomuch that I believe instances could now be produced, of entire pages without a single semicolon." More recently Kurt Vonnegut harrumphed that the only reason to use a semicolon is "to show you've been to college."
I believe all three esteemed gentlemen would be happy to learn that, in the 21st century, not just entire pages but entire books are published without the offensive dot and squiggle. I take minor issue with Mr. Vonnegut’s analysis, however. I think the semicolon’s use should show you've been to grammar school – and there is the rub. Schools gloss over so many of the basics these days in pursuit of grander theories of education that many students graduate grammar school, high school, and then college without ever learning to use semicolons. Consequently, they don’t, even when the graduates start to write for a living.
Yet, the mark is a handy one. A classic example from the 1885 edition of The American Printer notes the difference between “Charles the First walked and talked half an hour after his head was cut off” and “Charles the First walked and talked; half an hour after, his head was cut off.”
It is true that a period can serve in that example, too. In modern text, a period probably would be used, but it really doesn’t serve as well. Knowing when to stop is important in writing as in life, and most punctuation is intended to tell us just that, much like road signs. However, “slow,” “yield,” and “stop” signs on roads are not all one and the same; commas, semicolons, and periods are not interchangeable either. In principle, it is true, all yield signs could be replaced by stop signs, but this would impede the smooth flow of traffic. In principle, all semicolons between independent clauses could be replaced by periods, but this would impede the smooth flow of prose.
The humble punctuation mark always has had its defenders, which is why it still clings perilously to life. In 1943, an article in The Times bemoaned “the war that is being waged in some quarters on the semicolon." The author blamed pulp fiction, in which the action favors simple, short, rat-tat-tat sentences on pages rife with periods. “The semicolon is the enemy of action; it is the agent of reflection and meditation." So it is.
So, for anyone who has forgotten, the rules for its use are as follows:
1. Use between closely related independent clauses not conjoined with a coordinating conjunction (i.e. don’t use “and” or “but” to begin the second independent clause). Example: “I ate the burger; the dog ate the bun.”
2. Use between independent clauses linked with a transitional phrase or adverb. Example: “Maureen is gorgeous; moreover, she is rich.”
3. Use in a series containing internal commas. Example: “He owned three cats: one was long, black, and thin; another was short, white, and fat; and the last was calico and trim.”
Be aware, however, that obeying these rules might single you out when you are trying to be anonymous. In 1977 police were taunted by notes from the perpetrator of the Son of Sam crimes; one of the clues to his identity was his proper use of a semicolon.