I promised myself that I'd only spend an hour on this post, because rapid rivers of ink have gushed forth from those smarter and more qualified than I to opine on the matter of the use of singular "they." But a friend and colleague asked the other day whether it's right or wrong to use the singular "they," so let's have that conversation.

Neither right nor wrong

As with most usage issues in English, it's not as if there's a definitively right or wrong way to use singular "they." I say that with my descriptivist hat on: I'm trying just to describe how English gets used, not lay down proscriptions about whether it should be used in this way or that. The "should" approach is called the prescriptivist approach. We'll get to that. But the upshot is that you'll never hear me or anyone from the Laughing Saint Editorial's crew say that singular "they" is right or wrong per se. We're going to talk about whether it's appropriate once we get into the prescriptive side of things later on.

So, what are you going to learn in this post? A little bit about what other experts say, a little about gender theory, and a little about yourself.

Please ignore Grammar Girl

I've got a post I'm saving up about why Grammar Girl isn't your friend (do you use WebMD instead of a doctor? No. So you shouldn't use Grammar Girl and assume you've gotten accurate grammar/usage advice. I digress). That said, we do need to start this conversation by looking at what experts (i.e., not Grammar Girl) have said about the use of singular "they," both descriptively and prescriptively.

I'm a rhetorician with a background in linguistics (my dissertation director was a nationally-recognized linguist who helped create the Dictionary of American Regional English, and I have something like a master's worth of coursework in English grammar, including English-language history and functional, cognitive, and generative grammars), which means I think of language/linguistics as the foundation of rhetoric. Rhetoric is, more or less, how we use communication--verbal and otherwise--to do things. Note the importance there of the word "use." "English language usage" refers to customs of language usage, not the rules (flexible and dynamic though they may be) of grammar, which is really about how words get put together to make sense (but whether they achieve some purpose, well, that's a question for rhetoric and usage and style rather than grammar). Grammar is how the Lego blocks fit together; rhetoric is whether you've used your blocks to make a castle or a bridge and why you'd want to build one or the other.

So, before we can understand whether and how to use (!) singular "they," we have to understand its basis in language and the history of the language. The fact is that singular "they" has been used in the English language since before "correct spelling" was a thing. There's something like four centuries of time lag between the two, actually: singular "they" is at least as old as the 14th century, and spelling and other matters of language use were being codified in the 18th and 19th centuries. That's just the descriptive facts. So the historical argument suggests that there's precedent both for using singular "they" and for not using it, as language standards started to be implemented.

Since history won't save you, how about the brain? Here's a great analysis from the Bible of approachable linguistics scholarly news, Language Log, about how using the singular "they" has been shown to require increased processing time (meaning: it does seem to take a handful of milliseconds longer to understand what "they" or "their" refers to when it refers to a singular noun). But we're talking about milliseconds, not a complete breakdown in semantics (how sentences make meaning). So cognitive arguments aren't going to save you, either, because it would be patently risible to claim that understanding singular "they" creates such a significant cognitive burden that singular "they" should never be used.

What about semantics, though? Can you argue that the use of singular "they" creates vagueness in sentences that can't be overcome? Actually, I think this is the best argument against using it. Note that the sentence "The student took their book to class" makes perfect sense to some folks. To me, it causes at least momentary confusion: Wait, did this person intend to use "their"? Are we suddenly talking about some other group of people? Did I miss the change in subject or meaning? Grammatically, we can change the rules (or change them back) such that "they" is officially alright to use in singular contexts, but just like I have to read some sentences a couple of times before I understand whether "read" is past or present tense, I might have to read a sentence that uses singular "they" a couple of times before I'm assured of whom we're talking about, and there might still be some ambiguity. Furthermore, at the moment, we don't allow for "themself," which would be the singular reflexive form of the plural pronoun, which suggests to me that we're still not there, descriptively, when it comes to the singular use of the plural pronoun. I could be asking for too much (we use "themselves" as the singular reflexive instead), but I think that when we get to "themself," we'll be fully in singular "they" semantics. Right now, we're not.

On the ground

That said, when it comes to language use on the ground, some folks use singular "they" to promote a gender-neutral perspective. In many ways, I support this, but that's not my only reason for using singular "they," though I don't use it all that often (see the semantic argument against it, above). That said, I do use singular "they" not only in speech but occasionally in my Oratoria posts and elsewhere. There are good reasons to use singular "they," just a few of which include:

Respecting other people's wishes when it comes to the pronouns they prefer. Don't be a self-righteous jerk: if someone asks that you use "she" or "they" or "he," just do your best to do that. There's no reason to make a big deal about it. If that person changes their (!) mind about it later (an argument I've heard against having to keep up with personal pronoun choices), what's it to you? You can be forgiven slip-ups, in that case, but remember that most of the time, making that kind of change isn't something an individual takes lightly, so don't plan on being asked to adjust more than once per person.
Accepting linguistic (and social) change. It's not so much that words change, but our use of and rules for them change. Happens all the time. Don't imagine that you've got the form of English that G-d loves best. Unless you've got some stone tablets lying about that you wanna tell us about, and those tablets are about grammar and usage, there's no reason to be upset about language change. Unless you're trying to use language as a tool of oppression or control, that is.
It fits the context you're writing or speaking for. If I'm editing a blog post written for a website geared to people in their teens, I'm giving a pass to singular "they." If I'm editing a book written by one of my clients in the business world, there shall be no singular "they" if I have anything to say about it. The Chicago Manual of Style is unequivocal about their rejection of singular "they" (I have to believe it's because it occasionally creates ambiguities that can't be resolved semantically/grammatically), for example. So is The New Yorker. As a rule, for me, I decide to allow singular "they" if and only if:
1. It doesn't create ambiguities that can't be resolved easily by the reader
2. The applicable style guide allows for it
3. The audience is likely not to have a fit about it
4. The writer wrote it (i.e., I won't go adding it where it isn't already).

So, it's not as if this is a right-or-wrong issue. It's really a matter of rhetoric: how do you plan to use singular "they," and why? Will it work in your specific context? Those are the salient questions.