I am becoming increasingly conscious of a quality which my art acquires as it comes to rule my life as well. Rapid and abrupt changes of mood from one extreme to another are an essential part of my nature; moreover, it is true that extremes of emotional tension can scarcely do otherwise than impinge on each other—a fact which frequently saves the reason. [...] I am now inclined to call my subtlest and profoundest art the "art of transition," for the whole fabric of my art is composed of such transitions. I have come to dislike the harsh and precipitate; often it is unavoidable and necessary, but even then it ought not to occur except where the temper of the audience has been so definitely prepared for a sudden transition that it actually demands it. My greatest masterpiece in the art of very subtle, very gradual transition is, no doubt, the big scene in the second act of Tristan and Isolde. At its opening, the act presents life abounding, palpitating with all its fiercest emotions; at its close, the most sacred, most fervent yearning for death. These are the two opposite poles, and now, child, let us see how I have united them, how the transition from one to the other has been accomplished! Well, that is a secret of my musical form, which, I am bold to assert, for unity, for balance, for clear comprehensiveness, combined with detail, has never before been even dreamed of. [...] I have never been more horrified than when cuts in my operas were proposed here, as, for instance, in Tannhäuser. It was in this opera that I first worked with a growing sense of the beautiful, convincing necessity of transition, and, between the outburst of horror at Tannhäuser's hideous confession and the devotion with which, at length, Elizabeth's intercession is heard, introduced a very significant transition motif of which I have always been proud and which has never failed to get its effect. You can easily imagine what I felt when I learned that here (as in Berlin) people saw nothing but long-windedness, and straightway struck out an essential portion of my work of art. [...]
I picked out our dear Schiller from amongst my books. Yesterday I read The Maid and became so musically attuned that I was able to fill in the silence of Joan at her public accusation most excellently with notes. Her own fault—the wonderful one! To-day a speech of Posa (at the end of Act II.) upon innocence and virtue has absolutely amazed me, on account of the incredible beauty of the poetic diction. How sorry I am not to be able to accede to a request recently made me by the committee of the Schiller Festival in Berlin to write a song upon it! [...]
Source: Letters of Richard Wagner, Vol. 2, selected and ed. Wilhelm Altmann, trans. M. M. Bozman (J. M. Dent & Sons, 1927), No. 442