While your high-school English teacher may have told you not to use this construction, it actually dates back to at least the 14th century, and was used by the following authors (among others) in addition to Jane Austen: Geoffrey Chaucer, Edmund Spenser, William Shakespeare, the King James Bible, The Spectator, Jonathan Swift, Daniel Defoe, Frances Sheridan, Oliver Goldsmith, Henry Fielding, Maria Edgeworth, Percy Shelley, Lord Byron, William Makepeace Thackeray, Sir Walter Scott, George Eliot [Mary Anne Evans], Charles Dickens, Mrs. Gaskell, Anthony Trollope, John Ruskin, Robert Louis Stevenson, Walt Whitman, George Bernard Shaw, Lewis Carroll, Oscar Wilde, Rudyard Kipling, H. G. Wells, F. Scott Fitzgerald, Edith Wharton, W. H. Auden, Lord Dunsany, George Orwell, and C. S. Lewis.
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. So it's time for anyone who still thinks that singular "their" is so-called "bad grammar" to get rid of their prejudices and pedantry!
With pl. An instance of being present. rare.
a1635 SIBBES Emanuell ii. (1638) 10 There were divers presences of Christ, before Hee came
Though I suspect in SAE it is treated like the word "wheat"; a plural form technically exists, but is rarely used since the singular form covers both.
posted by RavinDave at 11:06 PM on December 8, 2004