Like the great European modernists, Ellington believed that form was inextricable from content. However, by sticking to the concepts and ensembles of jazz, he distinguished himself critically from Gershwin, Copland, and other American composers who used European models. Yet the difference is not simply formal. The essence of jazz is improvisation; no other music relies so much on the art of composing in the moment, and Ellington’s music builds not only on the sonorities of his band’s instruments, but the character of the men who played them, expressed in their unique patterns of improvisation.
Link from Arts and Letters Daily.