The 7th mode of melodic minor

Anyone that has attempted to play jazz knows that improvisation is a great deal of the job. Sometimes jazz gets defined by its improv style.

Now, chords are scales broken in pieces or intervals. Therefore, improvising over a jazz harmonic sequence will require that one plays on the appropriate scale over the appropriate chord. Therefore, an academic standard has been created on this issue. Not bad at all until one gets to question the why behind the what. 

There is a particular chord on a minor progression that responds to a scale that is not precisely the one in place of the chord. Even academically speaking, jazz schools of thought will agree on this. 

This phenomenon happens in the altered chord or that fifth chord on the 2 - 5 - 1 minor progression. Often times (more like always) this chord is altered in most of its passing tones. The 3rd and 7th stay, and of course the root and fifth are there. Now, the 9th, 11th, and 13th may get altered. This means a #9, b9, #11, b13, etc. 

So here is the issue to be aware of!  The scale to play here is the 7th mode of the melodic minor scale usually, and not the 5th mode even though the chord is the 5th chord. Of course, you can play the 5th mode as well but we are speaking here about best practices in jazz. 

Again, the issue to keep in mind is that although the chord is acting as the 5th in the progression, the mode to improv on will usually (practically) become the 7th mode of the scale and NOT THE FIFTH MODE AT ALL :)

Why is that? The answer is very much related to the way we hear!  More on a later post.