We all know that the diminished scale can be used to solo over diminished seventh chords and their associated dominant seven flat nine chords, but what about other harmonic resources contained within this scale? To review, the diminished scale is a symmetrical octatonic scale made up of alternating whole- and half-steps or half- and whole-steps. Either form will work over diminished seventh chords since the chord tones remain intact appearing as every other note but with different passing tones. For example:
C-Db-Eb-E-F#-G-A-Bb-C (half/whole diminished scale)
C-D-Eb-F-F#-G#-A-B-C (whole/half diminished scale)
Notice how the first, third, fifth and seventh tones are the same in both forms (chord tones of the diminished seventh chord) but the notes in between change. The important part is that the tones of the chord are present in the scale. The fact that the chord tones occur on strong beats makes things even better.
I noticed that we can also generate four major and four minor triads from this scale. Since these triads make use of some passing tones we must be a bit more careful in our scale choice. Let’s take the first example, the half/whole diminished scale.
Major triads are C (C-E-G), Eb (Eb-G-Bb), F# (F#-A#-C#) and A (A-C#-E). Of course many of these are enharmonic spellings.
Minor triads are Cm (C-Eb-G), Ebm (Eb-Gb-Bb), F#m (F#-A-C#) and Am (A-C-E).
This got me thinking about how we can use this scale over certain polychords associated with altered dominants. One of my favorite sounds has always been the polychord F/Gb meaning an F major triad with a Gb bass. (This could refer to any major triad with a bass note one half-step above its root). Usually this sound is associated with an altered dominant, one of which you may know as a dominant thirteen flat nine without a root.
The plan is to take this polychord and move it up in minor thirds, corresponding to the minor third relationships within the diminished scale that produced the major triads, and generate new and what I think are interesting “dominant” sounds. All tones are contained within one diminished scale so we can use the same scale to improvise over all four dominant sounds.
The examples should make things clearer. I used a ii-V-I progression in the key of G major inserting the new polychord as a dominant substitution. I labeled the polychord as a “slash” chord as well as a traditional dominant seventh chord including the altered tones so you could compare it to the standard altered dominant. Since many of these polychords are new structures it is not possible to use tertian harmonic designations to accurately describe them, so the harmonic indications are approximations but the traditional dominant descriptions will give you some point of reference.
When improvising, use the diminished scale shown at the top of the page for all four polychords. Also experiment with arpeggios of the four basic major triads that make up the polychords, either separately or even more interestingly in combination, as a way of exploring new altered dominant sounds in a fresh, contemporary way. For example, the next time you are soloing over a D7 chord try playing F, G#, B and D major triad arpeggios over this chord. I think you will find the sound interesting. Again, notice the minor third relationships between these major triads; it makes it much easier to remember which triads to use, especially when using them in combination.
There are numerous enharmonic spellings as well as enharmonic labeling of the polychords. The intention was to make the comparisons simpler between the two sets of voicings as well as making the voice-leading clearer in the musical notation.
One other thing; try different resolutions of the polychords. I chose to use GMaj7 to illustrate all the inversions of this chord but you can resolve to any G major type chord for variety and even smoother voice-leading.