In the argument over the programming of Broadway musicals by Australia’s opera companies, it is usually assumed that audiences know the difference between the two forms. But even superficial markers can be misleading. Bizet’s Carmen (1875) uses dialogue and song forms that are traditionally associated with the musical, but is classified as an opéra comique. When it was transposed into English as Carmen Jones (1943), with even less dialogue than the original, it was inexplicably classified as a musical. Stephen Sondheim himself, notoriously indifferent to opera, acknowledges the arbitrary nature of categories in his book Finishing the Hat (2010): ‘When Porgy and Bess was performed on Broadway it was a musical; when it was performed at … Covent Garden it was an opera.’