just noodling around, I started with Am7, I switched that to a b5, then my ear wanted it to resolve to Gmaj7. I had no intention of starting the Am7 as a II chord, I was just messing around. Looking at the note structure of the Am7b5, normally it would be a VII chord for the Bb major scale. The notes of the Am7b5 being A, C, Eb and G, I just can’t see why Gmaj7 (G, B, D, F#) works. Any help would be greatly appreciated.
There are probably a few reasons but the first thing that springs to mind is the Am to G (ii-I) does resolve fairly naturally. Take a chord progression you’ve probably heard many times, starting on the IV and working down to the I. In the key of G this would be C, Bm, Am, G. You can hear in this progression that Am does resolve to G fairly naturally, even without having a V-I cadence (D-G). It’s just the last chord in the descending sequence.
The other thing are the leading tones. Notes a semitone apart tend to resolve quite naturally, so if we look at the notes in the three chords…
Am7: A,C,E,G
Am7b5: A,C,Eb,G
GM7: G,B,D,F
We have the C going down to B and the Eb moving down to D, both a semitone apart.
The other thing to realise here is playing these three chords in sequence we get a chromatic movement going on, which always feels like it’s going somewhere: E > Eb > D.
A straight G major will also resolve nicely but it’s not unusual for a chord progression to end on maj7. Think of a typical ii-V-I, used very commonly in jazz and often played with 7ths. In the key of G this would be Am7 – D7 – GM7.
Your progression is just substituting the V with a ii7/b5, or that’s at least another way you could look at it.
