The subtitle for Mozart’s Così fan tutte may be ‘The School For Lovers’, but it’s as a school for directors that the opera is most instructive. From four lovers and two different romantic pairings, the composer spins a parable whose moral is as elusive as its morals. Faced with so much ambiguity (and so little political correctness) directors tend either to sand down the rough edges with laughs, or fling a capacious concept over the whole lot.