Well, here I go again! This time the short-cut for remembering the information comes from Bob Palmieri, an extraordinary guitarist, photographer, and my instructor from grad school. Here it is:
“The natural extensions of a major seventh chord and dominant seventh chord create a major triad up a whole step. The natural extensions of a minor seventh chord create a minor triad up a whole step.”
So what does all this mean? Extensions are the 9th, 11th and 13th above the basic seventh chord of 1, 3, 5, 7. Natural extensions are the ones that will sound most consonant or “natural.” If you apply this to each type of seventh chord here’s what you get:
CMA7: C E G B (D F# A) (chord scale, C lydian: C D E F# G A B)
C7: C E G Bb (D F# A) (chord scale, C lydian b7: C D E F# G A Bb)
Cm7: C Eb G Bb (D F A) (chord scale, C dorian: C D Eb F G A Bb)
O.K., so why F# in the first two chords? It avoids a dissonance between the third and eleventh of the chord. Also, notice that the chord scales just rearrange the notes of the chord into a scale (my “Lydian Talk” and “Lydian b7” posts look at this from the opposite direction).
So, as in the previous posts, I start to think, hmm:
CMA7 (9, #11, 13) = D/CMA7 = D/C bass =???
C7 (9, #11, 13) = D/C7 = D/C bass (again?) =???
Cm7 (9, 11, 13) = Dm/Cm = Dm/C bass = Lots of things to keep one busy!
Keep all of this in your purview (a nice word I learned from Bob Palmieri).