Chord substitution

ii ... IV
III, vi ... I
VIIo ... V ii ... IV
III, vi ... I
VIIo ... V

GENERAL COMMENTS

Chord substitution overview:

• Any chord in the dominant family can substitute for another dominant family chord
• Any chord in the major family can substitute for another major family chord
• Any minor can substitute for another minor family chord

Okay now the complicated explanation
Chord substitution can be a complex and wonderful thing. For the sake of simplicity, we'm not going to cover extended chords here like 9ths, 6ths, add whatever and all of those. We're going to stick to our basic chords from the Circle of Fifths and the chord scale tones. This will provide us with a good idea of how most substitutions in progressions work and give us some ideas to try to incorporate into our writing.
The idea that chords can substitute other chords depends and the fact that chords have feelings, tensions and
directions. A chord with a different feeling, tension or direction than the one you want to change or substitute simply won't work. It will end up sounding out of place or awkward.
So what we need to do is find out what the chord is that shares the same tension, feeling or direction.
Now obviously, based on all the stuff we just went over in the chord leading, chord scale tones, and circle of fifths
section, figuring our why is probably going to be an in-depth endeavor. But let's give it a shot to see if we can't figure it out. Actually, we may even already know the answer. We'll see.
First let's look at all the notes that chords share in a Key:
grey are shared notes

	1	2	3	4	5	6	7
C
dm
em
F
G
am
Bdim

yeah...and?
1. Every note is shared between 3 chords. So what happens is that every chord shares 2 notes with at least 2 other chords.
2. So why can't we substitute any of these for any of the others?
Because it has to do with what tones these chords share. As we stated already in the chord leading section, there are notes that are restful, moderately restless and restless.
The chords that share restless tones Tonic Category I iii VI
The chords that share moderately restless tones Subdominant Category ii IV
The chords that share restless tones Dominant Category V VIIo
Chord Substitution Summary:
any chord from the tonic category can probably substitute for any other tonic chord.
any chord from the subdominant category can substitute for any other subdominant chord.
any dominant chord can substitute for any other dominant chord.