In The Infinite Variety of Music, written in 1966, Leonard Bernstein discusses his method of writing music involving a kind of "trance state."
"All art recognizes the art the perceded it, or recognizes the presence of the art preceding it. So that it is not unlikely that your concept, the idea that will come to you in this trance, has something to do with music that has preceded it. And, in fact, even those composers who call themselves 'experimental' composers (and who are dedicated to the idea of writing music that is different from all other music that preceded it, making their music valuable only because it is different from earlier music) are admitting their recognition of the presence of art that preceded their own, because their art is still being written in terms of the art that preceded it--only this time in antithesis instead of imitation. Is that too confused? Yes. To put it another way, even experiemental composers, revolutionary composers, self-styled radicals, are, in writing revolutionary music, recognizing the music that preceded them precisely by trying to avoid it. Therefore, in a sense they are composing in terms of the music that preceded them."
"But more important than this, the concept is conditioned by this crazy, compulsive urge to say something. We always hear a distinction made between good and bad creators on the ground that the good creator had something to say--'Something To Say' is the big, magic phrase--and the bad artist didn't have 'Something To Say.'"