personal pronouns - Usage of "they" / "them" / "their" when the person's gender is not known

I know that one can use "they" / "them" / "their" in place of "he" / "him" / "his" or "she" / "her" / "hers" when the subject's / direct object's gender is not known; for instance, just looking at the default user's about me section on Stack Exchange sites:

Apparently, this user prefers to keep an air of mystery about them

My question is what happens when someone wants to reference the subject using a pronoun instead.

Should the verb be conjugated accordingly to the pronoun? E.g.:

Apparently, they prefer to keep an air of mystery about them

Or should the conjugation be retained? E.g.:

Apparently, they prefers to keep an air of mystery about them

The former looks unclear because it wouldn't allow the reader / listener to understand if the writer / speaker is talking about a single person or about a group of people, however the latter sounds very weird, at least just to the non-native speaker which I am.

Answer

Despite the fact that you're referring to a singular person, yes, the custom is always to maintain the same grammatical pluralization you would if you were using "they"/"them"/"their" in the more conventional sense. The SE phrasing, "Apparently, they prefer to keep an air of mystery about them", is therefore grammatical (including the last bit, for that matter), and the alternative is wrong enough in all cases that just about any native speaker would immediately notice and be jarred by it.

The only way to use singular verbs in such a case is to switch to a different pronoun. Using "it" to refer to people is extremely dehumanizing, so that leaves only two choices:

• the awkwardly slashed "s/he" and similar (including "he or she", hat tip Steve Jessop in comments)


• new words like "zhe", "ze", "zie", "zir", "hir", and so forth, which are relatively unfamiliar and confusing to anyone outside certain circles. (Especially because of the ridiculous number of ideas people have had for such new words.)

Usually, it's not worth the hassle. Just use "they"/"them"/"their" with plural verbs. No sane person will get offended, there's no grammatical problem, and stylistically the plural pronouns are arguably the least annoying in most cases.