The bulk of So What is based on D dorian. In fact, the form of the piece (AABA) repeats over and over throughout. Each a section based on D dorian and each B section, a half step up, on Eb dorian. The first 32 bar statement of the form, has the rhythm section and horns (in jazz, this is taken to mean all the wind and brass instruments in the front line) playing together establishing the syncopated, 2 chord ostinato. The following statements are successive solos by members of the band beginning with trumpet, followed by tenor then alto saxophone, then piano. This extended, slow moving harmony built on a modal scale rather than a set of functional chords in a progression is the hallmark of the modal jazz style.

The harmonic material in the two-chord ostinato heard throughout the piece can be analysed through traditional jazz means as Em11 and Dm11 respectively; however, they are not working functionally as either chord and it is unlikely that they would have been composed with these sonorities in mind. Modal jazz features quartal harmony (chords built on fourths) and these chords are built from the bottom up in fourths with the exception of the top note (E, A, D, G, B and D, G, C, F, A). The voicing of these chords and the slow rate at which they move indicates that the use of these chords is about the sound world of the mode and not a functional jazz chord progression.

Miles Davis – So What – Spotify