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I have just read in Emma by Jane Austen a phrase which surprised me:
I can think of but one thing - Who is in love with her? Who makes you their confidant?
(Jane Austen: Emma, Chapter VIII, Obreey PocketBook)
Here the lattest who is clearly in singular (followed by makes), the gender of the person under question is unknown, so I understand it as a gender neutral their:
Who makes you his/her confidant? Who has confided you the information about her lover?
I wouldn't expect such an old usage of their functioning as a singular gender neutral word. I've always considered this "grammar trick" as a much more modern invention.
Is it really a usage of the gender neutral their? Is it so old that Jane Austen could have used it? Or was it just some recent editor who didn't consider the good old Austen "correct enough" and "fixed" it?