It begins with a squinting of the eyes. Hm. A semicolon. You approach it with caution. Ok, I can do this. One dot, plus a comma. There. No, wait. That doesn’t look quite right. The questions begin: ...

Cecelia Watson, author of “Semicolon: The Past, Present and Future of a Misunderstood Mark.” Historian and philosopher of science. Faculty member in Bard College’s Language and Thinking program.

The age-old semicolon is dying out as Britons admit to never or rarely using the punctuation mark. In English-written 19th century literature it appeared once in every 205 words, but today it is down ...