http://en.wikipedia.org/wiki/Chord_substitution
Listen to this:
http://www.youtube.com/watch?v=W7lTjD8BFyY
No focus on 1:50 as he talks about it...
Fascinating! I've been working on this not knowing what it's called!
In fact reading on how the 5's dim 7 or the sharpened 5 dim 7 both work in other apps is the solution to what my ears couldn't figure out!
Also things like ommited the roots since the bass or keys has it.
Complimentary chords like relative minors or sneaking in say a Cmaj7 for a G, etc...
Loving this stuff.

expansive quality, and we all know that is a good good thing.
