On guitar, if you’re playing a chord on its fundamental state, with the root on the 5th string, on the 6th string you have its V grade.
That implies that, if you’re playing the V grade on another string, you can move the V degree to the 6th string, play an inversion and substitute the V degree for another note. That opens endless possibilities.
Some examples:
- You’re playing a C7b9 like this
Now move your third finger to the 3rd fret of the 6th string. You’re playing now a C7b9. Or, a Gdim7. Because… the notes are the same.
- You’re playing a C9
Do the same thing. Move the C to the G on the 3rd fret. You’re now playing a C9/G… or a G-6.
Things get weirder when you get into dominant chords…