“I played over the music of that scoundrel Brahms. What a giftless bastard! It annoys me that this self-inflated mediocrity is hailed as a genius.” – Pyotr Ilyich Tchaikovsky
Diary entry for October 9, 1886, quoted in Nicolas Slonimsky, Lexicon of Musical Invective (1953), p. 73.

“He came as a true friend, to share with me all my sorrow; he strengthened my heart as it was about to break, he lifted my thoughts, lightened, when it was possible, my spirits. In short, he was my friend in the fullest sense of the word. I can truly say, my children, that I have never loved a friend as I loved him; it is the most beautiful mutual understanding of two souls. I do not love him for his youthfulness, nor probably for any reason of flattered vanity. It is rather his elasticity of spirit, his fine gifted nature, his noble heart that I love… Joachim, too, as you know, was a true friend to me, but… it was really Johannes who bore me up… Believe all that I, your mother, have told you, and do not heed those small and envious souls who make light of my love and friendship, trying to bring up for question our beautiful relationship, which they neither fully understand nor ever could.” – Clara Schumann
In her journal, as quoted in Johannes Brahms : A Biography (1997) by Jan Swafford, p. 164

“Applying here Brahms’ contributions to an Unrestricted Musical Language will enable the opera composer to overcome the metrical handicaps of his libretto’s prose; the production of melodies and other structural elements will not depend on the versification, on the meter, or on the absence of possibilities for repetitions. There will be no expansion necessary for mere formal reasons and changes of mood or character will not endanger the organization. The singer will be granted the opportunity to sing and to be heard; he will not be forced to recite on a single note, but will be offered melodic lines of interest; in a word, he will not be merely the one who pronounces the words in order to make the action understandable. He will be a singing instrument of the performance. It seems-if this is not wishful thinking-that some progress has already been made in this direction, some progress in the direction toward an unrestricted musical language which was inaugurated by Brahms the Progressive.” – Arnold Schoenberg
“Brahms the Progressive” (1933)