The employment of the myth or legend as a subject for dramatic treatment recommended itself to Wagner also on a purely musical ground, which Peri could not discover in the crude condition of musical art in his day. Myths are embodiments of human types, of fundamental traits of character and of elementary emotions. They have the advantage of universality. They are free from conventions of time and place. Thus Wagner saw that the employment of mythical subjects would permit him to concentrate the whole power of his musical expression upon character and emotion, which are just the things within the scope of operatic music. Every one of his music dramas makes action and the pictorial elements of the drama subordinate and accessory to the expression of the emotions of the scene. In working out this plan he came upon the final and fundamental law of his theory, namely, that there must be in a music drama an organic union of all the arts necessary to the expression of the emotions of the scene to the spectator. Text, music, action, and scenery must all unite in a common purpose, and their union must be so complete that no one element can be taken away without injury to the whole. From this law Wagner derived the corollary that he must write his own text, and so he did. All his librettos are his own, and they are not mere schemes of dialogue, arias, processions, and ballets, but remarkably fine dramatic poems. The text being written, according to Wagner all the other elements in the drama, music, action and scenery, must be devoted to the fullest and most convincing expression of the emotions contained in that text. Now the conveyance of emotion is within the power of music, and the more completely the music can be devoted to this, the more successful it is likely to be. The use of the myth enabled Wagner to make perfect his organic union of the arts tributary to the drama, because it focused the music upon the emotions, and so carried the other elements to the same point. This principle--concentrating the musical expression upon the emotion--led Wagner to adopt a new musical form. He writes what has been called "continuous melody." That is, there are no set arias, duets, or ensembles in his later works, but all the dialogue is carried on in a free arioso form, and duets are simply the musical conversation of two people. Wagner wrote voluminously in regard to his theories, and on this point he says:--