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Hiro's Jazz Theory

How to run a cool improvisation on a diminished chord™

You practice diminished scales. You play the practiced scale on your improvisation. Unless the material is Brazilian music, which calls for a diminished sounding lines, it will sound too diminished, or too practiced. When you listen to giants like Miles Davis, you won’t hear such lines.

Besides, as explained in my Jazz Theory Workbook, figuring out the correct scale in the tonal context isn’t easy for sight-reading. Here is something I came up with when I am in that situation, and it works well.

What Schöenberg Said

Schöneberg's Harmony

The one of the most important 20th Century composers, Arnold Schöenberg notes a diminished 7th chord is an extension of a dominant chord with lowered 9th and omitted root (p.348 “Theory of Harmony” ISBN 0-520-04944-6).

Let’s take a look at what is being talked here.

When a C#dim7 chord appears in the key of C Major, followed by a D-7 chord, it is a diatonic functioning diminished chord, “I#dim7". The theoretically correct chord scale would be as follow:

C# diminished

This C#dim7 chord can be understood as an A7(♭9) without root, functioning as V7(♭9)/II, and the expected chord scale is a perfect match.


When you see a diminished chord, and if you could identify it as a diatonic functioning diminished chord quick enough on your sight reading, all what you need to do is to call up your cool Dominant 7th ♭9 lick on the Major 3rd below the root of the diminished chord.

But things might not be that simple when you are sight reading on stage. What if you see a Bb dim7 chord, which you couldn’t tell if diatonic functioning or not? The Major 3 blow is G♭. What if you are not comfortable with G♭(♭9) lick?

Finding a Hook

This is an example of a non diatonic functioning diminished chord in another well known standard song, As Time Goes By, starting at its bridge:

As Time Goes By
Whether the changes are correct or not, you are facing this onstage, sight reading. There is no way the A diminished chord is acting as a diatonic functioning chord, since it is not followed by a half step or the same root. See my workbook.

You must be able to see the chord tone of A dim7. Seeing a chord tone right away is essential to improvisation. Once you see a chord tone, you should see four dominant chords because a diminished 7th chord is built on 2 Triplicated-Tones and 1 Triplicated-Tone is shared by 2 dominant chords: 2 x 2 = 4

A dim7
The note on the A dim7 chord which does not appear in those four dominant chords becomes tension notes or scale note if not available as tension. Let’s examine.
  • G♭ does not appear in F7 » F7(♭9)
  • B7 is a good match with A dim7 » B7(♭9): This has to be the Mixo ♭9 scale because of the -3rd note of A dim7, which is ♭9 to B7.
  • E♭does not appear in D7 » D7 (♭9,♭13): Tension♭13th is added because of the context, that is, proceeded by F-7 and followed by C-7.
  • A♭7 is also a good match with A dim7 » A♭7(♭9): This has to be the Mixo♭9 scale because of the root note of A dim7, which is ♭9 to A♭7.

Any one of them will work. You pick one that you like, and blow away.

Just add ♭9th, but what about ♭13th?

Let’s step back. Here is the summary of the steps, which you need to process in a split second on the stage when sight reading:

  1. Up in the air, write the chord tones of the diminished 7th chord
  2. Produce four dominant chords which share the tritones with the diminished 7th chord
  3. Pick one of them you like, hopefully, the one closest to the context, as explained
  4. Add ♭9th then blow

Since we are accustomed to adding the ♭13th when we blow such phrase, would it work in this situation? It works most of the times, as I did on the D7 to A dim7 example. On the other hand, ♭13th of A♭7 is F-flat, and it will take away from the context. In any case, improvising on live show does not need to be theoretically correct, while it is still important to know what you are doing.

End of this subject.

Theoretically correct scale

Here is an except from Someday My Prince Will Come, bar 9 – 12:Someday My Prince Will Come

The D♭diminished 7th chord appears as a tonal functioning diminished chord, ♭III diminished 7th, that is, analyzed as passing from III-7 to II-7. The non chord tones of the tonal functioning diminish chord are determined by the Key of the Moment, B♭, in this case.

The theoretically correct scale will be as follow:


Note that parenthesized numbers indicate avoid notes.

A lot of double-flats. As we discussed in the Workbook, we can respell the Db diminished scale to the C# diminished scale for conveniences. After all, theoretical correctness is not required when you are on stage and blowing hard.


Note that parenthesized numbers indicate avoid notes.

What Can You See?

A diminished 7th chord is, again, built with two tri-tones, which means it could represent four dominant chords:


Let’s try to fit these chords to the key of B♭, which is the key of the moment of this song, Someday My Prince Will Come. This is not a theoretical analysis since we are not considering what chord might follow.

  • A7 = possible V7 of III minor: the scale would be Altered Mixo
  • But on stage, we often like to play A7(♭9,♭13) instead, to make it more interesting (or out of Be Bop habit)
    A7(♭ 9 ♭ 13)
  • E♭7 = possible SubV of III minor: the scale would be Lydian♭7/Mixo #11
    E ♭ 7
  • C7 = possible V of V: the scale would be Straight Mixo
  • G♭7 = possible SubV of V: the scale would be Lydian♭7/Mixo #11

Which one of them has all the chord tones of C#dim7? The answer is A7 (♭9,♭13).

Let’s compare the scale:

C#dimA7(♭ 9 ♭ 13)

If you add C natural, which is a #9th of A7, and often added when the b9th is used (because augmented 2nd jump is considered disturbing), the resulting scale is identical. Coming up with a cool phrase on A7 (♭9,♭13) is a lot easier than sight reading C#dim7 and trying to figure out the non chord tones according to the key of the moment.

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