Q. When talking about “the turn of the century” (from 1899 to 1900), should it be “the turn of the nineteenth century” or “the turn of the twentieth century”? It seems that since the years 1800 to 1899 have been referred to as the nineteenth century, then the turn from 1899 to 1900 should be referred to as “the turn of the nineteenth century.” Please advise.

A. There is no general agreement about what a phrase like “turn of the nineteenth century” means. It does seem to suggest the “turn of the nineteenth century into the twentieth”—i.e., the change from 1900 to 1901 (or, popularly, 1899 to 1900). But it’s probably best to stick to the more general phrase “turn of the century” and to limit it to a context that makes the century in question clear—for example, in a discussion surrounding the immediate legacy of Theodore Roosevelt’s charge up San Juan Hill. See CMOS 9.32.