Q. This is from today’s op-ed column in the Washington Post: “Two top fundraisers for Newt Gingrich quit Tuesday. . . . Neither Thomas nor Heitman returned an e-mail seeking comment on their departure.” Should that pronoun be plural, really?
A. If the departure was a joint one, then “their” is apt; if the departures were individual and unrelated, “his departure” is Chicago’s preferred phrasing. Although the use of “their” in place of a singular pronoun has been discussed endlessly in online forums, and many language experts have accepted it as standard usage, CMOS still considers it to be informal (see CMOS 5.227) and recommends against using it in formal writing. You can Google “their as singular” and catch up on this conversation.