"So What" and/or "Impressions" are very challenging tunes ! It is not the melodies, nor the harmonic complexities-- there are only two chords after all. It is... the form. To put it more precisely, it is the very simplicity of the form that makes it tricky for a lot of improvisers to keep track of where they are in the tune. And slowing down the tempo only makes things worse because it gives us even more time to lose our place... It is interesting to note that the tempos of Miles Davis' live versions of "So What" were getting faster and faster with the years. You may want to check out the albums "Live At The Olympia, March 21, 1960" or "Live At The Plugged Nickel" for some ridiculously fast tempos.

Here is the basic 32-bar AABA form, which is the same for both tunes:

||: Dm7 (Dorian) :|| 8 measures (repeated)
| Ebm7 (Dorian) || 8 measures
| Dm7 (Dorian) || 8 measures

The ironic thing is that those tunes are always presented to beginning improvisers. Sure, there aren't any real "changes" to speak of, and it gives people a chance to practice their "Dorian" runs. The truth is that a lot of players have a hard time knowing exactly what section they are in ! After the bridge modulation, we have to deal with 3 consecutive A sections--that's a total of 24 bars of Dm7... before we see the next Ebm7 again.

So here comes the concept of "Chordal Thinking": I find it helpful to create some internal harmonic movement within each section. We don't need to actually play those extra chords, but if we just THINK of them, it delineates the form much more clearly.

By adding some basic Minor cadences, we can break down each 8-measure section into smaller segments:

| Dm7 | Em7b5 A7 | Dm7 | Em7b5 A7 |
| Dm7 | Em7b5 A7 | Dm7 | (A+7) ||

(note: I will only write out the examples over the A Section. For the B section (Ebm7) just transpose everything up a half-step. Also, the optional A+7 at the end of the example should only be played to set up another section in Dm7. We can then place this chord at the end of sections A1 and A3, but not at the end of section A2 which is followed by the bridge)

Now, we are not thinking strictly "modally" anymore, but all the superimposed harmony will generally work against an open Dm7. The bass player and/or the chordal accompanist don't even need to know that the soloist is thinking of substitutions. In fact, I don't really see those as substitutions. It simply is "added movement".

If we think of D Dorian as being the ii chord in C Major, we can then superimpose any of the diatonic chords:

CM7   Dm7   Em7   FMaj7   G7   Am7   Bm7b5   (as seventh chords)
C   Dm   Em   F   G   Am   Bdim   (as Triads)

Of course, some of those chords will sound better than others, and even if theoretically all the notes are correct (they all are found in a D Dorian scale) we need to use our ear and decide which ones we like best. An important detail to keep in mind while choosing a chord sequence is to retain a logical root movement.

Examples 2-5 illustrate the use of diatonic chords used as alternate chords for the A section.

| Dm7 | Em7 | Dm7 | Em7 |
| Dm7 | Em7 | Dm7 | (A+7) ||

| Dm7 | Em7 | FMaj7 | Em7 |
| Dm7 | Em7 | Dm7 | (A+7) ||

| Dm7 | Em7 | Dm7 | CMaj7 |
| Dm7 | Em7 | Dm7 | (A+7) ||

| Dm7 | G7 | Dm7 | G7 |
| Dm7 | G7 | Dm7 | (A+7) ||

We might be getting further and further away from the original harmony, but this last example is an interesting variation, inspired by the tune "Full House" by Wes Montgomery:

| Dm7 | G7(13) | Dm7 | G7(13) |
| Dm7 | G7(13) | 1. Bb7(13) | A+7 ||
| 2. Bb7(13) A+7 | Dm7 ||

Again, even when the bass player is still playing Dm7 throughout, our alternate chords will help us map out the tune-- the sections no longer feel like a never-ending Dm7 vamp. Furthermore, spelling out diatonic chords over Dm7 will also bring out some beautiful extensions:

for example: Em7/D = Dm7(9, 11, 13) and G7/D = Dm7(11, 13)

I will end this chapter with a question: with a little stretch of the imagination, could we say that "So What/Impressions" is the equivalent of "Rhythm Changes" transposed to a Minor key ?



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