Chord substition is a great way to get some extra millage out of the chords you already know. It’s also a great technique to find new ways to come up with interesting progressions. The basic idea is to use one chord in place of another.
Let’s start with a few simple examples.
C6 = Am7
Cm6 = Am7(b5)
With these two examples, they are the same because they share the exact same notes.
If we compare C6 (root position) to Am7 (1st inversion) we can see that both chords share the exact same notes. So this means that wherever you use an Am7 chord, you can replace it with a C6 and vise versa.
Cmaj9 (no root) = Em7
Cm9 (no root) = Ebmaj7
C9 (no root) = Em7(b5)
Cm(maj9) (no root) = Ebmaj7#5
These next set of substitutions are a great way to visualize 9th chords. It’s never a good idea to play the roots when there’s a bass player, they take care of that better than we can. These substitutes give you 9th chords and help you avoid getting in the bass players way.
As we see in the examples above, removing the root from any 9th chord leaves us with a 4 note chord. Each one is a simple chord which can be voiced as a Drop 2 voicing and used in place of the 9th chord. Let’s look at an example using Drop 2 voicings.
Another example illustrating Cm9 voiced as an Ebmaj7.