Thank you for this discussion. I am interested in these questions too. There does seem to be some important knowledge that the specialist composers had. Harrison Birtwistle referred to the 'latent ritual of Western classical dance'. What ever did he mean? He observed that Stravinsky got 'the knowledge' from Tchaikovsky, who got it from Minkus and Drigo? This then lead to the combination of ballet and art music that dominated the Twentieth Century. Those composers who spent time in the dancer's world tended to make successful ballets: Gluck, Tchaikovsky, Stravinsky rather than Mozart, Beethoven even though they collaborated with Noverre and Vigano