diminished scale
I use this a lot over dominant seventh chords. It’s worth discussing because it’s so very useful. This is a recap of discussion from a forum I participate in. I editied and simplified it a lot though.
Here’s what I consider the five key ideas for using the diminished scale.
1) they go with dominant seventh chords
A dominant seventh chord has its third and seventh forming the interval of a tritone, which you can view as the equal division of an octave into two parts. With the root and fifth removed, the dominant seventh chords with roots a tritone apart are equivalent–this is the well-known “tritone substitution.” The symmetry of the diminshed scale is a nice fit for the symmetry of the dominant seventh. For example, C7 dim scale is the same as F#7 dim scale, just as C7 is a valid substitute for F#7.
2) there are only three
Classical theory tends to consider two different diminshed scales–the half/whole, and the whole/half. I find it more useful to associate a half/whole dim scale with a dominant seventh chord, and consider the whole half as just a mode of the diminshed scale (which is symmetrical). There are only three unique dim scales for you to learn. (so no excuses). C7, Eb7, F#7, and A7 all share the same dim scale, it just starts at different points. That’s why the half/whole versus whole/half distinction isn’t useful to me. For me what’s useful is associating a scale to a dominant seventh chord. The following image spells the three scales.
click the image to download a PDF version
3) almost all the alterations
the dim scale contains the chord tones of the dominant seventh chord, plus these alterations:
b9, +9, +11, 13
So it makes sense to use over any dominant seventh with extensions, the notable exceptions being natural 9, and b13, which we have other scales to handle (maybe another thread for this).
4) the four triads
the dim scale can be resequenced into a series of major triads whose roots are a minor third apart. For the dim scale associated with C7:
C E G / Eb G Bb / F# A# C# / A C# E
This makes for some interesting patterns, as well as substitutions beyond the common tritone sub. Arpeggiating A7 over a C7b9 chord would be an example of that type of sub. Various interesting upper structure voivings are formed by the dim scale. For the C7 dim scale again:
Eb/C7 (C7+9)
A/C7 (C13b9)
and the very dissonant
F#/C7 (C7b9#11, but I don’t really hear it in that way)
5) goes great with minor tonic
dominant sevenths with alterations lend themselves better to cadences that resolve to a minor tonic. this scale contains all the chord tones of the minor ii-V. But that doesn’t mean you can’t reach for the dim scale if you resolve to major. And it’s at its best (for me) in extended jams over a single chord. To solo over C7#9 I’ll typically be reaching into the dim scale for a lot of vocabulary–if you play a lick, repeat it up or down a minor third and it’s still in that dim scale. Play an interval, and then transpose it and invert it. There’s a million ways to do melodic patterns with this scale thanks to the symmetry.
