Probably the average opera-goer is contemptuous of the libretto, because he thinks it is an easy task to write the mere words of an opera. To him, no doubt, the opera lives by its music, and by its music alone. But there is really no warrant for this uncomplimentary attitude. An opera is a music-drama, and if it is to achieve success, wide-spread and long-lasting, its drama must be as effective as its music. Experience proves that, so far from being as easy as it seems, the construction of a satisfactory libretto is really a difficult feat, to be achieved only by an expert in stage-craft. It is no task to be confided to an amateur play-maker, to a mere lyrist, ignorant of the art of the theater. First of all, a satisfactory book must contain the skeleton of a good play; and, second, this must be the special kind of play which will not only inspire the musician, but afford him a succession of special opportunities for the exercise of his own art. The book of an opera must be a good play; and more than once have we seen a libretto deprived of its music and written out again in prose for production in non-musical theaters. 'Carmen' is one example of this transformation. The late Sir Henry Irving was so taken with Wagner's 'Flying Dutchman' that he had it made over into a play for his own acting--'Vanderdecken.' The book of an opera must be a good play, and therefore not a few successful operas have been composed on plots which had already won approval as plays on the stage. Indeed, many modern composers are so convinced of the necessity that librettos shall be attractive in themselves that they are continually borrowing popular plays to deck with melody. 'Salomé' and 'Pelléas et Mélisande,' 'Madam Butterfly' and 'Cavalleria Rusticana,' the 'Bohème' and the 'Tosca' were all successful without music before they were set to music to win a second success. The book of Verdi's 'Rigoletto' is based on Victor Hugo's drama, 'Le Roi s'Amuse'; and oddly enough it was the operatic libretto, rather than the original poetic drama, which suggested the English play on the same theme, Tom Taylor's blank-verse drama, the 'Fool's Revenge.' Another of Verdi's librettos was borrowed from Hugo's 'Hermani', while his 'Traviata,' as we all know, is taken from the play of the younger Dumas, long popular in America as 'Camille.' Two of Verdi's latest operas had Shaksperian themes, 'Otello' and 'Falstaff.'