>>150065414
The Oxford English Dictionary traces singular they back to 1375, where it appears in the medieval romance William and the Werewolf.
In the eighteenth century, grammarians began warning that singular they was an error because a plural pronoun can’t take a singular antecedent. They clearly forgot that singular you was a plural pronoun that had become singular as well. You functioned as a polite singular for centuries, but in the seventeenth century singular you replaced thou, thee, and thy, except for some dialect use. That change met with some resistance. In 1660, George Fox, the founder of Quakerism, wrote a whole book labelling anyone who used singular you an idiot or a fool. And eighteenth-century grammarians like Robert Lowth and Lindley Murray regularly tested students on thou as singular, you as plural, despite the fact that students used singular you when their teachers weren’t looking, and teachers used singular you when their students weren’t looking. Anyone who said thou and thee was seen as a fool and an idiot, or a Quaker, or at least hopelessly out of date.
