Operetta: mother or sister of musical comedy?

The history of French ‘light operatic genres’ (genres lyriques légers) is a curious one. Denigrated by posterity from the 1960s onwards, it has also been the battleground for a pointless and unfounded internecine conflict: the artificial opposition between operetta and musical comedy. The former supposedly represents the decadence of Romanticism, the latter the verve and wit of modernity: a clash between the ‘pass ’ and the ‘trendy’, as it were. How has this come about?