i’ve been trying to distill the little I know into cheat sheets. thought other people might find it useful too. haven’t QA-d it might be wrong
Borrowed chords:
to try and break out of predictable chords that are diatonic to the key you are playing in, you can borrow chords from other modes that have the same root note, most commonly borrowing chords from the minor scale in the major scale, but any of the modes can work.
in addition when moving between chords that have a space in-between (like C to Dm in the key of C major) you can fill that gap with a diminished 7 chord, and it will work (diminished 7 chords can resolve to any major or minor chord one note up or 2 steps down)
Harmonic Minor/Major
Harmonic minor just sounds super dramatic and spooky, and it has all these bonus chords that work, the F can be Major, Minor, Major/Minor, or diminished, the E can go from major to augmented, just loads of ways to work in the tension. The B diminished 7 is completely symmetrical so any of its 4 notes can become the root note and you can cascade the chord up and down, there are loads of different voicings and fragments of the chord that work really well as like add-ons to other chords, same with the C augmented 5th which any of the 3 notes can become the root.
With normal A minor you can switch to the relative major of C but that doesn’t work here as there is no G note so it is a C augmented chord, i’m not sure if they are supposed to go together but the C harmonic major scale works really well with the A harmonic minor, as it shares all the weird chords, the diminished 7ths and augmented chords.
Another bonus of those diminished 7th chords is because of their symmetrical property you can use it as a pivot chord to key change all over the place, to any major or minor chord one note up or two steps down from any of its four notes.
that is about everything I know on music theory gleaned from youtube videos, could have got it wrong though
