'Singular "their" etc., was an accepted part of the English language before the 18th-century grammarians started making arbitrary judgements as to what is "good English" and "bad English", based on a kind of pseudo-"logic" deduced from the Latin language, that has nothing whatever to do with English... And even after the old-line grammarians put it under their ban, this anathematized singular "their" construction never stopped being used by English-speakers, both orally and by serious literary writers.'
