points which were contained in the verse, and influenced the construction of the musical idea, were to him co-operating but not dominating elements. The words of an opera have a definite object; they provide foundation and support for the musical expression, and are not therefore absolutely independent, as in the drama,[39] but are obliged to recognise and respect the laws of music, as well as those of poetry. To attain this end a compromise is as indispensable as in every other union of the sister arts. Architecture, in her highest achievements, turns for embellishment to sculpture and painting; and no one has ever doubted that in such co-operation each art must make some concession to the other. The architectural plan must be so conceived as to afford fitting space and position for the sculpture and painting; these, on the other hand, must be introduced with a view to the essential conditions of the building; the pediment, the arch, the metope are not freely selected forms, but constitute the limitations which arise from the necessities of the building. The sculptor modifies his style to suit the character of the building, the painter knows how to give significance to the whole design by skilful composition and combinations of colour on the flat surface of the walls. Doubtless architecture, with her severe laws and inflexible forms, imposes restrictions on the fancies of the artist; but who can imagine that Phidias in the sculptures of the Parthenon, Raphael in the Loggia of the Vatican, renounced their freedom of design or their independence of execution in obedience to the will of the architect? The relation between poetry and music is of the same kind. Mozart saw the necessity for co-operation between the musician and the poet, if the right effect was to be given in its just proportions. The musician must be ready to "give some hints" which shall put the poet in possession of his intentions and of the conditions necessitated by the rules of his art; the poet must be "intelligent," clever, and cultivated enough to fall in with the intentions of the musician, and poet enough to retain his poetical powers in spite of these limitations. {MUTUAL RELATIONS OF MUSIC AND VERSE.} (229) Mozart is quite right in asserting that co-operation of this kind is the surest pledge for an altogether satisfactory opera; unhappily he is quite right also in declaring such a co-opera-tion to be attainable only by "a veritable phoenix."