Chord Substitution
In the previous lesson on Shell Chords, we learned that you don’t always have to play every single note in a chord. In fact, you can omit any note except for the 3rd and 7th (Guide Tones) of the chord and still retain the general sound or feel of the original chord.
For this same reason chords can be substituted. If the substitute chord contains the 3rd and the 7th of the substituted chord, the two chords will have a similar feel and so can act as substitutes for each other. The five most common chord substitutions found in Jazz are shown below.
| Substitution Name | Original | Substitute Chord |
|---|---|---|
| Median Note Substitution | CMaj7 | Em7 Am7 |
| Am7 | CMaj7 FMaj7 |
|
| ii-V7 Substitution | G7 | Dm7 G7 |
| G7 | Em7 A7 | Dm7 G7 | |
| II7-V7 Substitution | G7 | D7 G7 |
| G7 | E7 A7 | D7 G7 | |
| #Vdim7 Substitution | G7 | G#dim7 |
| Tritone Substitution | G7 | D♭7 |
But substituting chords and omitting notes are really the same thing; they are two sides of the same coin. For example, if we can omit any note other than the 3rd and 7th, then we can omit the root. If, then, we take a CMaj7 chord (C E G B) and extend it to make a CMaj9 (C E G B D) and then drop the root note, we get an Em7 (E G B D) which is a Median Note Substitution for a CMaj7. So an Em7 is a rootless CMaj9. This is why chord substitution works.
So we find that a sad chord (Em7) also sounds like a happy chord (CMaj7), which is interesting.
Chord Ambiguity
So again we find that chords are very ambiguous. They depend on the note that’s being played in the bass (the bass-note) and on the chord that’s played before and after that particular chord (the chord progression).
For example, let’s take the notes E G A and C. Now, these four notes can be:
- a C6 chord (C E G A);
- an Am7 chord (A C E G); or
- a Rootless FMaj9 chord ([ ] A C E G).
And the only way to tell the difference is by looking at the chord progression and at the bass-note. The most common chord progression that establishes the tonic chord is a V-I perfect cadence. So if we have:
- a G7 going to that collection of notes (C E G A) with a C in the bass, then we have a C6;
- an E7 going to that collection of notes (C E G A) with an A in the bass, then we have an Am7;
- a C7 going to that collection of notes (C E G A) with an F in the base then we have an FMaj9.
In Practice
As mentioned in previous lessons, a Jazz musician would never play a song exactly as written on a lead sheet. Instead, he or she would add tensions or use chord substitutions to make the chord progression more interesting. Below are a few examples of how a II-V-I in the key of C can be made more interesting and complex by using extensions, alterations and substitutions. Notice also that a substituted chord can be further extended and altered.
| Original Progression | Dm7 | G7 | CMaj7 |
|---|---|---|---|
| Substitution #1 | Dm11 | D♭9 (tritone sub) | CMaj13#11 |
| Substitution #2 | FMaj9 (median note sub) | G13 | Am9 (median note sub) |
| Substitution #3 | Em11 - A7♭9 | Dm11 - G7♭9 (ii-V sub) | CMaj9 |
| Substitution #4 | Bm7♭5 (median note sub) | Bo7 (#Vdim7 sub) | Am7 (median note sub) |
Notice that Bo7 (B D F A♭) is the same chord as G#dim7 (G# B D F) only from a different root note. Diminished chords repeat every minor 3rd interval. This was done so the bass notes moved smoothly (i.e. in small intervals) and didn’t jump around too much.
We will discuss chord substitution in much more detail when we learn about Jazz Reharmonization.