Ink, blood and bile. In 1837, two University of Paris law professors clashed over a question of semicolon usage and decided to settle the matter with a duel. A rogue semicolon drifted into the retranscription of an early-20th-century statute, causing liquor service to be suspended in Boston for six years. In 1945, a semicolon inserted into the definition of war crimes in the Charter of the International Military Tribunal threatened to halt the prosecution of captured Nazis until the ambiguous sentence was clarified.

Why such confusion? The modern semicolon was invented in Venice, in 1494, by the printer and publisher Aldus Manutius, and, for much of history, it had no strictly defined function. It acted like a musical notation, allowing for a pause somewhere between the beat of a comma and a colon (hence its mongrel design). Only later was it systematized and given two primary uses.

Image Cecelia Watson’s new book is “Semicolon,” a biography of the unusually controversial punctuation mark. Credit... Tomila Katsman

The first is uncontroversial. The semicolon keeps a sentence tidy by separating items in a list already cluttered with commas. (The band played shows in Richmond, Va.; Memphis, Tenn.; and Asheville, N.C.). The second function has caused all the strife. Here, the semicolon takes the place of a period and yokes together two independent clauses that could function as sentences on their own. (The band is terrible; I regret following them on tour.)

In this second capacity, semicolons are discretionary. They add shading, allow one thought to ripen into another. Few have used the mark more liberally and eccentrically, or more beautifully described its psychological effect, than Virginia Woolf. From the Lily Briscoe section of “To the Lighthouse,” describing Lily’s summers with the Ramsay family: “Such was the complexity of things. For what happened to her, especially staying with the Ramsays, was to be made to feel violently two opposite things at the same time; that’s what you feel, was one; that’s what I feel, was the other, and then they fought together in her mind, as now.” Semicolons allow these sentiments to flow together — to jostle and harmonize — in one sentence the way they would in one mind.