Diminished Scale Cadences
I was watching a Barry Harris masterclass video about the diminished scale, where he was talking about groupings of four dominant chords based on their relation to the same diminished scale. I was already aware of this concept, having learned about the diminished scale and that any note of a diminished 7th chord could be lowered by a half step to create a dominant chord. What struck me is that since these four dominant chords are related, could the dominant V in a ii-V-I progression be substituted for any of its three "siblings"? How would these related cadences sound compared to the straight V? I decided to investigate.
The first step is to choose a ii-V-I progression.
Now that we have a diminished 7th chord, we apply the concept that you can lower any one note of the chord to get a dominant chord. As there are four notes in a diminished 7th chord, you get four different dominant chords based on one parent diminished 7th chord. If you lower the F to an E, you get E7, which is what we started with. That's our baseline.
Starting from the Fdim7 again, you next you drop the B to a Bb.
This gives you a Bb7, which is the tritone substitution of the V! I always thought that the main reason tritone subs work is because the 3rd and 7th are the same as the original dominant chord, and the strong descending chromatic bass movement of 9 to b9 to 1- and these are still true- but further validating its use (on a theoretical level) is that it is a derivative of the parent dim7 chord based on the diminished scale, which relates it to the original dominant V chord.
In this example I've added an E in the bass. While it's acceptable to play a straight Bb7 chord, I was interested how it would sound in combination with the traditional 5 to 1 cadence, which is another note from the diminished scale. The result is the sounding of the #11, which implies a lydian dominant sound. Again, this provides new validation for using lydian dominant harmony over tritone subs. The reason I've always had for this is that the #11 is the 5 of the I, so you get some of the destination harmony before you fully resolve, which is true, but from this different perspective the #11 combines the tritone subsitution with the original V to I cadence with the movement from E to A.
Next, you drop the D to a C#.
This gives you a Db7 chord. This one is a little puzzling to me, but I think I have an explanation. In Db7 you have the notes Db, F, Ab, and B. As compared to E7, this highlights the notes 6, b9, 3, and 5. If you were to say E7(b9,13) that is how you annotate diminished scale harmony in a chart. And like the tritone sub, you have a strong descending chromatic line- but in a different place- from the F# (Bm7), to the F (Db7) to the E (Amaj7). If you can think of any other explanation let me know in the comments.
Including the E sounds out the #9. Again, this note adds another note from the diminished scale, which implies the original V to I cadence. So this Db7#9 resolves very well to the Amaj7.
Next move the Ab down to a G.
This gives you G7, which is a "backdoor dominant" to Amaj7. Again, this diminished perspective provides a new explanation/validation for the existence and use of the backdoor dominant.
Including the E over G7 gives you the 13th.
In the examples above I've kept the low E in the bass, but you can swap it out for any other note from the diminished scale and see how that affects the chord quality.
Now I'm wondering if these related dominant chords can be swapped out when the dominant is not resolving, such as in a blues.
The first step is to choose a ii-V-I progression.
Next, turn the dominant V into a rootless Vb9, which is a diminished 7th chord. Here, E7(b9) is equivalent to F diminished 7.
Starting from the Fdim7 again, you next you drop the B to a Bb.
This gives you a Bb7, which is the tritone substitution of the V! I always thought that the main reason tritone subs work is because the 3rd and 7th are the same as the original dominant chord, and the strong descending chromatic bass movement of 9 to b9 to 1- and these are still true- but further validating its use (on a theoretical level) is that it is a derivative of the parent dim7 chord based on the diminished scale, which relates it to the original dominant V chord.
In this example I've added an E in the bass. While it's acceptable to play a straight Bb7 chord, I was interested how it would sound in combination with the traditional 5 to 1 cadence, which is another note from the diminished scale. The result is the sounding of the #11, which implies a lydian dominant sound. Again, this provides new validation for using lydian dominant harmony over tritone subs. The reason I've always had for this is that the #11 is the 5 of the I, so you get some of the destination harmony before you fully resolve, which is true, but from this different perspective the #11 combines the tritone subsitution with the original V to I cadence with the movement from E to A.
Next, you drop the D to a C#.
This gives you a Db7 chord. This one is a little puzzling to me, but I think I have an explanation. In Db7 you have the notes Db, F, Ab, and B. As compared to E7, this highlights the notes 6, b9, 3, and 5. If you were to say E7(b9,13) that is how you annotate diminished scale harmony in a chart. And like the tritone sub, you have a strong descending chromatic line- but in a different place- from the F# (Bm7), to the F (Db7) to the E (Amaj7). If you can think of any other explanation let me know in the comments.
Including the E sounds out the #9. Again, this note adds another note from the diminished scale, which implies the original V to I cadence. So this Db7#9 resolves very well to the Amaj7.
Next move the Ab down to a G.
This gives you G7, which is a "backdoor dominant" to Amaj7. Again, this diminished perspective provides a new explanation/validation for the existence and use of the backdoor dominant.
Including the E over G7 gives you the 13th.
In the examples above I've kept the low E in the bass, but you can swap it out for any other note from the diminished scale and see how that affects the chord quality.
Now I'm wondering if these related dominant chords can be swapped out when the dominant is not resolving, such as in a blues.
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