The_Complete_Idiot%27s_Guide_To_Music_Theory

Replacing the I chord (C Major) with the vi (A minor) and the iii (E minor)—lots of notes in
common.
You can replace extended chords in the same manner, and actually end up with
more notes in common. For example, you can replace CM7 with either Am7 or
Em7, both of which have three notes in common with the original chord.
Major Chord Substitutions
Diatonic substitution is the theory; you’d probably rather know some hard-andfast
rules you can use for real-world chord substitution. Don’t worry; they exist,
based partially on diatonic substitution theory.
The following table presents four different substitutions you can make for a
standard major chord. Remember that the root of the substitute chord must
stay within the underlying scale, even if some of the chord notes occasionally
wander about a bit.
Major Chord Substitutions
Substitution Example (for the C Major chord)
Minor chord a third below 16FIG05
Minor 7 chord a third below
Minor chord a third above
The first substitution in the table is the standard “down a third” diatonic substitution.
The second substitution is the same thing, but uses an extended chord
(the minor seventh) for the substitution. The third substitution is the “up a
third” diatonic substitution, as discussed previously.
Minor Chord Substitutions
Substituting a major chord is relatively easy. So what about substituting a minor
chord?
Chapter 16: Chord Substitutions and Turnarounds 207