Hyphens, En Dashes, Em Dashes

Q. How would you handle “early-to-mid” + “century”? “Early to mid-twentieth century”? “Early-to-mid twentieth century”? “Early-to-mid-twentieth century”?

A. When these century phrases are used as nouns, we’d retain only the hyphen after mid: “in the early twentieth century,” “in the mid-twentieth century,” and, by extension, “in the early to mid-twentieth century.” But when they’re used as modifiers before another noun, extra hyphenation would be needed: “early twentieth-century history,” “mid-twentieth-century history,” and “early-to-mid-twentieth-century history.”

Two things to note: (1) It wouldn’t be wrong to refer to “early-twentieth-century history” (with two hyphens), but we think the extra hyphen (after early) is unnecessary (see CMOS 7.87—and note that early is an adjective, not an adverb, and therefore not subject to the -ly exception described in CMOS 7.86). (2) The word mid, unlike early, isn’t an ordinary adjective; instead, it usually combines with any word that it modifies—either with a hyphen (“mid-twentieth”) or without (“midyear”).

See also the hyphenation guide at CMOS 7.89, section 1, under “number + noun”; section 3, under “century”; and section 4, under “mid.”