More 8 tonic theory

In order to fully grasp the workings of the 8 tonic system we must first fully understand four tonic substitutions. Four tonic subs are also called diminished substitutions and the tri-tone substitution is included in this group of subs. If you can imagine that the tonic V7 and the tri-tone is one axis and that the V7 chords a minor third above and below is the other other axis (at a 90 degree angle from the first axis).

In the key of C the V7 is G7 and the tri-tone sub is C#7. The other two dominant chords are Bb7 and E7. These chords are all related to each other because they share the same diminished scale. A G7(b9), Bb7(b9), E7(b9) and C#7(b9) are basically all the same chord if you don’t consider their roots. The tri-tone is used all the time as the most common type of substitution, but the the other two dominant chords (Bb7 & E7) are also very common subs for V7. They are often used as ways to get to the tri-tone sub, this is called a ‘backdoor resolution’. 

For example:

D-7   G7    CMaj7

F-7 Ab-7  CMaj7

In fact, we can use the component chords of all four ii-7V7s and combine them freely.

B-7  E7    D-7 G7    F-7  Bb7    Ab-7  C#7

We can use only the dominants or only the ii-7s:

D-7       G7          CMaj7

G7 Bb7 E7 C#7   CMaj7

or play:
F-7       B-7         CMaj7

Keep in mind that the Dominant chords all sound pretty close to each other, the related ii-7s are where you start to get more dissonance. Think of the minor third axis  (B-7  E7, F-7  Bb7) as cousins of the tri-tone sub. The chords of the 8 tonic system are simply all of the chords from these these four ii-7V7s. When we are using hexatonics/pairs from these chords we are still basing the harmony these strong four tonic substitutions. The 8 tonic system is simply another way to apply hexatonics/triad pairs to diminished subs. We are just calling the related ii-7 chords Major triads (from the -3rd) or you can also think of them as IVs.


David Wilken said...

I think that in your first example you have a typo. Shouldn't it be a Bb7 instead of Ab-7?

David Carlos Valdez said...

No, that is correct. The Ab-7 is the related ii-7 of the tri-tone sub V7. So playing the Ab-7 over the G7 is effectively like playing the Db7.

David Wilken said...

Ah, I got you now. Slowly but surely...

Fotis said...

I've been using 4 dominants a minor third apart at the 5th, b2nd, 3rd, and b7 positions relative to the tonic for a while now. The effectiveness of looking at dominants functionally rather than merely diatonically dawned on me while studying Ted Dunbar's Tonal Convergence text.

Your posts are opening up another vista here. Unfortunately the dropbox links to the .pdf and audio samples in related 8 tonic theory blog entries are broken or the files are missing.

Would you please make these available again? I'm very interested in this material. Thanks so much.

David Carlos Valdez said...

Links are FIXED!