As a language lover, if there’s one thing that drives me nuts, it’s people who love English to death, that is, try to kill it with misdirected kindness. Case in point: I just overheard a rant about the iniquities of using singular they/their/them, as in my title above. He or she may not have said exactly this in his or her harangue, but essentially it was, “Everyone knows they should use singular pronouns with singular nouns.” However, and of course, they (not — ever! — “he/she”) wouldn’t have said that. In their eyes, “Everyone knows they…” is a mortal sin. They would have had to resort to something like, “Everyone knows a person should use…”

In this instance, style manuals have been glacially slow in catching up to vernacular usage. The two most commonly cited guides of recommended usage, the Associated Press Stylebook and the fussier Chicago Manual of Style, allow (as of 2017) the singular they/their/them — but grudgingly:

AP: “They/them/their is acceptable in limited cases as a singular and-or gender-neutral pronoun, when alternative wording is overly awkward or clumsy. However, rewording usually is possible and always is preferable.”

Chicago:They and their have become common in informal usage, but neither is considered fully acceptable in formal writing, though they are steadily gaining ground. For now, unless you are given guidelines of the contrary, be wary of using these forms in a singular sense.”

I’m surprised these paragons of good grammar aren’t still railing about you replacing thou! I get that, like dictionaries, style guides follow “street English” (“language of the gutter,” as I heard one self-professed “language maven” call it). That is, they’re a few years behind how folks like you and me actually speak and write. But in this case, it’s more like centuries! Their, used in the singular sense, has been around for over 600 years. (“Eche on in þer craft ys wijs.” = “Each one in their craft is wise.” Wycliffe’s Bible, 1382)

If someone really gets on their* high horse about this, you can point out the logic behind it. Take an example from Steven Pinker’s The Language Instinct, “If anyone calls, tell them I can’t come to the phone.” Anyone and them are not referring to the same person (—if they were, they really should agree in number). Them here is effectively a placeholder. As Pinker says about the hypothetical caller, “…there may be one, there may be none, or the phone might ring off the hook with would-be suitors; all that matters is that every time there is a caller, if there is a caller, that caller, and not someone else, should be put off.”

[* Microsoft Word spellchecker suggests “his or her.”]

All these storms in teacups come about because English, unlike most languages, doesn’t have a gender-neutral singular, like the French on (“Ici on parle français”) and the Spanish reflexive se (“Aqui se habla español”).

Incidentally, and happily, the gender-neutral he/his/him has now virtually disappeared (“No one shall be arbitrarily deprived of his nationality nor denied the right to change his nationality.” —  Article 15, Universal Declaration of Human Rights).

So if someone tells you you’re using the singular they incorrectly, tell them to their face that they’re wrong.