So says Merriam-Webster.
Here’s Benjamin Dreyer celebrating the decision in the Washington Post. As long as I’ve been around, people have been using “they” to refer to a person whose gender was unknown or irrelevant — and then, perhaps, feeling guilty about it. Or, we tried to recast the sentence to make the person in question plural, or we held our noses and used the awkward “he or she.” That dodge has become more than merely awkward as an increasing number of people reject the binary he/she as their pronouns of choice.
Merriam-Webster is fundamentally descriptivist, so this accolade doesn’t mean they are saying “they” must be used in this way. On the other hand, other organizations, like the American Psychological Association, have endorsed the usage. But what’s most important is that my cold-eyed editors reached the same conclusion earlier this year. There is, of course, no higher authority, This means that you can feel confident that you are doing the right thing when you use the singular “they.”
Go ahead. You know you want to.