HOW 3,4 AND 5 NOTES SUBSCALES COMBINE WITH CHORDS IN CHORD PROGRESSIONS
If we want to correspond simple patterns of harmony with simple patterns of melody then
1) Threechords in other words 3 consecutive notes subscales correspond to triads of chords that have distance of roots an interval of 2nd. And there are so many such 3-scales as are the notes of each chord. Furthermore threechords occur externally as linking bridges to consecutive chords of the chord progression, when the chord progression have roots that have a distance an interval of 3rd.
2) 5-chords in other words 5 consecutive notes subscales with total length an interval of 5th occur internally to each chord of the chord progression
3) tetra-chords in other words 4 consecutive notes subscales with total length an interval of 4th occur externally as linking bridges to consecutive chords of the chord progression, when the chord progression is an arc of the wheel by 4ths or more generally the roots of the consecutive chords differ by an interval at most of 4th.
THE MIRACULOUS TETRACHORD:
The previous explains why when improvising over a diatonic scale and a chord progression by chords of it, each time the chord changes, it is at most within a tetrachord that contains the last "staying" note (melodic center) of the last chord that we find the next "staying" note (melodic center) of the next chord.
