An amusing slip in the Daily Mail (online here), in an opinion piece by Dan Hodges on the decline of the Labour Party and its singularly unsuccessful leader Jeremy Corbyn. Hodges says that "anyone who thinks Labour's problems began on September 12, 2015, when Corbyn was elected, are deluding themselves."
It's unquestionably a grammatical mistake, of course. Not about pronoun choice, but about verb agreement.
Forms of the pronoun they, including its reflexive themselves, are fine with singular antecedents (despite what some prescriptive usage manuals say). In fact a Google search for the quoted string "anyone who thinks that is deluding themselves" produces at least 9 hits (more tomorrow, of course, because of this post and all those who reproduce it or quote it). But anyone who thinks Labour's problems began on September 12, 2015 is a singular NP, just like anyone who succeeds, or for that matter, anyone. Hence it takes singular agreement. The sentence quoted should have said this:
Don't let the length of the subject noun phrase confuse you. A noun phrase with anyone as its head simply cannot take plural agreement, as is clear from a shorter example:
How did the Hodges sentence slip by? It's possible that he wrote is but a subeditor saw is deluding themselves and, looking no further to the left than that, changed is to are on the basis of a subconscious grasp of frequency. (Notice, the Wall Street Journal corpus contains 111 cases of are VERBing themselves, with a wide variety of verbs, but only two cases of is VERBing themselves, both quoted from informal speech by people who are saying anyone who [blah blah blah] is kidding themselves.)
But it's also possible that Hodges slipped up, choosing are because he subconsciously noticed that the nearest noun to the left was Labour's problems, and the subeditor failed to catch it.
As with the etiology of most syntactic mistakes, we can guess but we'll probably never know.
Except that Bob Ladd points out to me that on Sunday The Guardian quoted former CIA director John Brennan as saying "Anybody who thinks I'm responsible for that are dead wrong." Here there are no distracting plural NPs.
Perhaps Brennan was making the verb agree with the semantics of an approximate paraphrase like "All the people who think that are dead wrong" — a sentence-planning error due to short attention span.
Or maybe it's just very hard to say things on the fly and never flub anything when you're talking to the press. Maybe people just screw up, randomly.
I don't know. Linguistics is science. We don't know everything. If we knew everything, we'd stop doing this; did you ever think of that?
The whole point of having a job that involves figuring out from evidence what the hell is going on with the speech and writing that most of the seven billion people on this planet are engaging in most of their waking hours is that we don't know how to explain what's going on, but we believe that by pursuing systematic investigations we can get a bit closer to knowing. See?