Duke Ellington was hardly a composer at all in the traditional sense. For centuries, both “classical” and “popular” composers had worked in solitude. They often collaborated with other people in the process, but they worked out their ideas by themselves.
Ellington composition didn’t usually come about that way. He didn’t compose for instruments. He composed for people, and he needed those people around him. Composers rarely share their procedures with the public, but Ellington briefly described his in a magazine article.
Sometimes he wrote out a melody, worked out the arrangement, and presented it to the band. That’s traditional composition, but not Ellington’s usual procedure. Sometimes he wrote a melody and simply played it for the band. Other times (not often), he’d sit at the piano after a gig and make up a melody on the spot. He’d play a little, talk about it some, and play a little more. The finished product came from all the band members contributing ideas.
Then the boys will start making suggestions in a “free-for-all.” One of them might get up and demonstrate his idea of what a measure should be like. Then another one of the bous will pick it up and maybe fix it a little. Sometimes we’ll all argue back and forth with our instruments, each one playing a couple of bars his own way.
Duke Ellington, “Swing Is My Beat!” New Advance (October 1944): 14 in Music in the USA: A Documentary Companion, Judith Tick, editor with Paul Beaudoin, assistant editor (Oxford and New York: Oxford University Press, 2008): 535.
Ellington’s article says nothing about the harmonies. If he supplied chords along with the melody, they changed during the free-for-all. If he supplied only the melody, the harmonies emerged during the free-for-all. It is, of course, impossible to present a melody without rhythm, but that, too, evolved as everyone in the band “argued back and forth.”
Once they came to an agreement, someone wrote out the arrangement. But the written arrangement was not the end of the matter. Ellington’s band had as many as half a dozen different arrangements of many pieces in the book.
An Ellington composition, is therefore a result of a group collaboration. Even the most carefully notated sections amount to written improvisations. It’s still an Ellington composition, though. He provided the original idea. He assembled the people who collaborated with him–and kept the same core group much longer than any other band leader did. He talked through the moods and colors that he had in mind.
Actually, Duke Ellington’s idea of composing an ensemble piece collaboratively and then writing it down later isn’t all that new. That’s how Medieval and Renaissance music came about! And it’s no longer unusual. Most rock music starts out with similar procedures.