I think you can really learn so much from "Kind of Blue". I think "So What" the first cut on the album features only 2 chords and the musicians just shift in and out of Scale modes to vary the mood. I think it only features a Dm7 vamp and Ebm7 vamp and starts out with a Dorian Mode lick and then goes beautifully haywire from there.
I think the musicians came in without rehearsing and Miles just had initial "sketches" of the chords and asked everyone to improvise their ass off (this is overly simplistic as these musicians were the best and had considerable knowledge of music theory).
They used super imposed scale modes to vary the mood.
Bill Evans is highly under rated for his contribution to this album. Listen to him as he frames Miles and Coltrane's lines with different chords to alter the mood of the music.
Galing.
Plus his liner notes on the album pretty much sums up Jazz improv for me.
"There is a Japanese visual art in which the artist is forced to be spontaneous. He must paint on a thin stretched parchment with a special brush and black water paint in such a way that an unnatural or interrupted stroke will destroy the line or break through the parchment. Erasures or changes are impossible. These artists must practice a particular discipline, that of allowing the idea to express itself in communication with their hands in such a direct way that deliberation cannot interfere.
The resulting pictures lack the complex composition and textures of ordinary painting, but it is said that those who see well find something captured that escapes explanation.
This conviction that direct deed is the most meaningful reflections, I believe, has prompted the evolution of the extremely severe and unique disciplines of the jazz or improvising musician.
Group improvisation is a further challenge. Aside from the weighty technical problem of collective coherent thinking, there is the very human, even social need for sympathy from all members to bend for the common result. This most difficult problem, I think, is beautifully met and solved on this recording.
As the painter needs his framework of parchment, the improvising musical group needs its framework in time,. Miles Davis presents here frameworks which are exquisite in their simplicity and yet contain all that is necessary to stimulate performance with sure reference to the primary conception.
Miles conceived these settings only hours before the recording dates and arrived with sketches which indicated to the group what was to be played. Therefore, you will hear something close to pure spontaneity in these performances. The group had never played these pieces prior to the recordings and I think without exception the first complete performance of each was a "take."
--- Bill Evans