Double Minor Major 7 Combos

Following up on this recent post that used the minor major 7 (mM7) chord, here's a quick description of what happens when you combine a pair of them. It turns out there are only three different ways to do this.

There are two ways to combine a pair of mM7 arpeggios such that none of the noes overlap: you can separate them by either a whole tone or a tritone. Both produce a Neapolitan scale with one added note, which doesn't sound very interesting but the separation of these collections of notes into a pair of disjoint arpeggios may lead you down some unexpected melodic paths.

For the record, combining the notes of CmM7 and DmM7 produces C Neapolitan with an added 2 (D):

while combining CmM7 with F#mM7 gives us C Neapolitan with an added 4 (F):

The only other possibility, it turns out, it to separate them by a major third. This produces a pentatonic scale that's just a mM7 with an added minor third (or augmented second, which might be a more logical way to think of it). Again, to be specific we play CmM7 and EmM7 and the combined result is the five-note scale C-D#-E-G-B:

That's Forte 5-21A; its inversion is 5-21B, which would be C-D#-E-G-Ab:

This has a similar sound but I'd think of it differently, as C-E-G (C major triad) plus G#-B#-D# (G# major triad):

This is a fragment of what I've elsewhere called the Coltrane cycle, which I think is a separate but related bit of vocabulary.