Originally Posted by: Douglas Showalter
Diminished 7th chords
Try and stay with me here. Diminished 7th chords consist of 4 notes; the root, b3, b5, and bb7 of a chord. Let's use Gdim.7 as an example. Those notes are:

G, Bb, Db, E

Now within that chord, we have 4 different tri-tones (the 3rd and b7th of a 7th chord.) In this case, a Gdim.7 chord can be used as a substitute for any of these 4 dominant 7th chords;

G and Db = Eb7
Bb (A#) and E = F#7
Db (C#) and G = A7
E and Bb = C7

Now, what keys do these all lead too? Here is how that pans out;

Eb7 = V chord of Ab
F#7 = V chord of B
A7 = V chord of D
C7 = V chord of F

Now you have four keys that all have a common thread. Ab, B, D, and F now have something in common. You will find when you break this down that you have nearly every possible major, minor, and diminished triad available to you. Therefore, you have now opened up your world of possibilities in songwriting.

However you want to approach it, those are a few techniques that hopefully are not too complicated and might work for you. Let me know if you grasp this OK. I know it's a little crazy.

Good luck! :o

Let me make a slight correction to this statement. It was recently brought to my attention that I explained this concept a bit incorrectly so let me make an adjustment.

When spelling a Dim.7th chord, the following notes apply;

1, b3, b5, bb7

That being said, you want to make sure when spelling out this chord that you name everything harmonically correct. In my example, I used a G dim7 chord as my reference. I spelled it like so ;

G, Bb, Db, E

The correct spelling is actually:

G, Bb, Db, Fbb

This being the case because this is how it would read on the staff, and that is ultimately what dominates how we name notes in music. E and Fbb are the same note, but in the context of this chord Fbb is what is harmonically correct. I apologize for this mistake and hope this clears this up a little bit. Thanks for bringing this to my attention and hopefully this concept benefits those reading this forum.

Thanks! :eek: