vociferous said:
And then, as now, it is a grammatical error.
Maybe in the minds of pedants who can only criticize how others abuse language. Singular they, particularly generic
they and epicene
they, are widely accepted as correct grammar.
Singular they is http://www.crossmyt.com/hc/linghebr/austheir.html#X1a", 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 they is acceptable according to http://www.merriam-webster.com/dictionary/they" :
usage They, their, them, themselves: English lacks a common-gender third person singular pronoun that can be used to refer to indefinite pronouns (as everyone, anyone, someone). Writers and speakers have supplied this lack by using the plural pronouns <and every one to rest themselves betake — Shakespeare> <I would have everybody marry if they can do it properly — Jane Austen> <it is too hideous for anyone in their senses to buy — W. H. Auden>. The plural pronouns have also been put to use as pronouns of indefinite number to refer to singular nouns that stand for many persons <'tis meet that some more audience than a mother, since nature makes them partial, should o'erhear the speech — Shakespeare> <a person can't help their birth — W. M. Thackeray> <no man goes to battle to be killed. — But they do get killed — G. B. Shaw>. The use of they, their, them, and themselves as pronouns of indefinite gender and indefinite number is well established in speech and writing, even in literary and formal contexts. This gives you the option of using the plural pronouns where you think they sound best, and of using the singular pronouns (as he, she, he or she, and their inflected forms) where you think they sound best.