Among my fellow punctuation nerds, I have a reputation as someone who has no use for semicolons. I don’t hate semicolons; I hate writing about semicolons. Fortunately, now I don’t have to, because Cecelia Watson, a self-identified “punctuation theorist” who teaches at Bard College, has written a whole book about them: “Semicolon: The Past, Present, and Future of a Misunderstood Mark.”

At first, I thought Watson was doing with the semicolon what Simon Griffin did with the apostrophe in “Fucking Apostrophes” (2015). Both are slim volumes about an element of language that gives people endless grief. But whereas Griffin, an adman, provides straightforward rules, albeit with a bushel of exceptions (and a running joke: every use of the word “apostrophe” is preceded by a profanity), Watson, a historian and philosopher of science and a teacher of writing and the humanities—in other words, a Renaissance woman—gives us a deceptively playful-looking book that turns out to be a scholarly treatise on a sophisticated device that has contributed eloquence and mystery to Western civilization.

The semicolon itself was a Renaissance invention. It first appeared in 1494, in a book published in Venice by Aldus Manutius. “De Aetna,” Watson explains, was “an essay, written in dialogue form,” about climbing Mt. Etna. Its author, Pietro Bembo, is best known today not for his book but for the typeface, designed by Francesco Griffo, in which the first semicolon was displayed: Bembo. The mark was a hybrid between a comma and a colon, and its purpose was to prolong a pause or create a more distinct separation between parts of a sentence. In her delightful history, Watson brings the Bembo semicolon alive, describing “its comma-half tensely coiled, tail thorn-sharp beneath the perfect orb thrown high above it.” Designers, she explains, have since given the mark a “relaxed and fuzzy” look (Poliphilus), rendered it “aggressive” (Garamond), and otherwise adapted it for the modern age: “Palatino’s is a thin flapper in a big hat slouched against the wall at a party.”

The problem with the semicolon is not how it looks but what it does and how that has changed over time. In the old days, punctuation simply indicated a pause. Comma, colon: semicolon; period. Eventually, grammarians and copy editors came along and made themselves indispensable by punctuating (“pointing”) a writer’s prose “to delineate clauses properly, such that punctuation served syntax.” That is, commas, semicolons, and colons were plugged into a sentence in order to highlight, subordinate, or otherwise conduct its elements, connecting them syntactically. One of the rules is that, unless you are composing a list, a semicolon is supposed to be followed by a complete clause, capable of standing on its own. The semicolon can take the place of a conjunction, like “and” or “but,” but it should not be used in addition to it. This is what got circled in red in my attempts at scholarly criticism in graduate school. Sentence length has something to do with it—a long, complex sentence may benefit from a clarifying semicolon—but if a sentence scans without a semicolon it’s best to leave it alone.

Watson has been keeping an eye out for effective semicolons for years. She calculates that there are four-thousand-odd semicolons in “Moby-Dick,” or “one for every 52 words.” Clumsy as nineteenth-century punctuation may seem to a modern reader, Melville’s semicolons, she writes, act like “sturdy little nails,” holding his wide-ranging narrative together. She is delighted with the “springy little semicolons” of Irvine Welsh in “Trainspotting” (“The sweat wis lashing oafay Sick Boy; he wis trembling”) and she has a special fondness for the rare semicolon in Raymond Chandler, whose hardboiled private detective, Philip Marlowe, is not given to periodic sentences. In “The Big Sleep,” for instance, Marlowe describes his room: “In it was everything that was mine, that had any association for me, any past, anything that took the place of a family. Not much; a few books, pictures, radio, chessmen, old letters, stuff like that.” In Watson’s perception, that choice of a semicolon after “Not much” creates a reflective silence. “The semicolon reads as Marlowe having to stop to think.”

A sentence from Wittgenstein contains a “fantastically vague semicolon”: “Der Philosoph behandelt eine Frage; wie eine Krankheit.” (“The philosopher treats a question; like an illness.”) This has been translated by G. E. M. Anscombe thus: “The philosopher’s treatment of a question is like the treatment of an illness.” But, in removing what Erich Heller, an expert in German philosophy, calls a “profound” semicolon, one that “marks a frontier between a thought and a triviality,” the translator has reduced a deep thought to a bland one. Watson writes, sounding like the “punctuation therapist” she sometimes plays, “Ambiguity can be useful and productive, and it can make some room for new ideas.”

Watson is especially thought-provoking on the topic of semicolons and the law, where ambiguity can lead to trouble. In Massachusetts, a semicolon that should have been a comma would have prevented hotels from selling liquor after 11 P.M.; it had the effect of making people buy a lot of drinks before last call. Worse, in a New Jersey murder trial in 1927, sloppy punctuation caused one of the defendants, Salvatore Rannelli, to be sentenced to life imprisonment while the other, Salvatore Merra, was sentenced to death—for the same crime. Legal cases are often built on precedent, and a judgment based on flawed punctuation sets a bad precedent, which can perpetuate injustice.

The semicolon’s two main detractors, the antiheroes of Watson’s book, are Donald Barthelme and Kurt Vonnegut, with Chandler complaining about a proofreader at The Atlantic (one Margaret Mutch) and Mark Twain weighing in on the ignorance of proofreaders in general. Barthelme found the semicolon “ugly as a tick on a dog’s belly.” Vonnegut wrote that semicolons are “transvestite hermaphrodites representing absolutely nothing,” a statement that makes me feel only more sympathy for the semicolon. What’s wrong with hermaphrodites?

Henry James, who would have been my choice for Master of the Semicolon, turns out to have been famous during his lifetime for his use of dashes. Watson writes that the dash “cutting a path” through any page of James is “an arm outstretched as a barrier to keep one thought from tumbling into the next.” She has unearthed an interview, from 1915, that James gave to a reporter for the Times, in which the Master (who did not do interviews, and on this occasion insisted that the reporter note “his punctuation as well as his words”) remarked that dashes “strike both the familiar and the empathic note . . . with a felicity beyond either the comma or the semicolon; although indeed a fine sense of the semicolon, like any sort of sense at all for the pluperfect tense and the subjunctive mood . . . seems anything but common.” Watson observes, “We live in the Era of the Dash”—which is probably just as well.

Both the dash and the semicolon are put to brilliant use in a page-and-a-half-long sentence from “Letter from Birmingham Jail,” which Watson quotes in full. In it, Martin Luther King, Jr., details the miseries of a black man, a victim of injustice, who is asked to wait patiently for change. King piles up clause after clause, each describing a more harrowing, frustrating event than the last, and each lofted by the semicolon that concludes the one before: “when you are humiliated day in and day out by nagging signs reading ‘white’ and ‘colored’; . . . when you are forever fighting a degenerating sense of ‘nobodiness.’ ” The litany rises to a crescendo delivered with a dash: “—then you will understand why we find it difficult to wait.” Watson concludes that “this is mimesis at its finest”; the semicolons hold the prose “in suspension,” and the reader in suspense, waiting, along with King, for justice. Of course, King’s letter is about much more than punctuation, but here is an instance in which the semicolon did its small part for civil rights.