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I have found that there are conflicting views on what is considered the diminished scale in jazz and when to play it. If I have a ii-V- I in C and would like to apply a diminished scale to create a line on the V7 chord containing the chord tones of G7 (G,B,D,F) would I use the G whole/half diminished scale or the G Half-Whole diminished scale?

In order to improvise with them I would need to be able to apply them without too much thought. How should I visualise the diminished scale when I see the G-dim chord symbol? In the context of a G7 chord, I could theoretically just visualise the semitone below the G7 chord tones i.e Bb, Db, E and Gb. But I can't say if this method is a valid method of learning the diminished scale.

This confusion really rules out using the dim scale for me. Practising the scale up and down doesn’t help. I think my approach is totally wrong.

  • You can use the G Mixolydian scale to improvise on that very same V7 chord of C Major despite G not being a chord tone of all kinds of 3-note chords you can make with the G Mixolydian scale (Am, Dm, F, etc.). Get used to hearing nonchord tones when using a scale to improvise on a chord. – Dekkadeci Dec 9 '19 at 8:26
  • What makes you say that using any dim scale, or the notes thereof, over V or V7 in a piece? – Tim Dec 9 '19 at 11:45
  • Half whole would give you the b9 and the #9 while whole half would give you 9 and #9, miss the 3rd and give you 4. – ggcg Dec 9 '19 at 11:55
  • use of the diminished scale on dominant chords is an option due to the tensions in the diminished scale which fit well with the dominant sound. – Robert Buckley Dec 9 '19 at 15:54
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I would not use the G whole-half diminished scale to create a line on the V7 chord of a ii-V7-I chord progression in C Major. I would use the G half-whole diminished scale instead.

The G whole-half diminished scale is G-A-B♭-C-D♭-E♭-E-F♯ and sadly does not contain a B♮, unlike the V7 chord of C Major (which is a G7 chord).

The G half-whole diminished scale is G-A♭-B♭-B-C♯-D-E-F and notably contains all 4 notes of the V7 chord of C Major: G, B, D, and F.

Pick the diminished scale that contains the notes of the chord you want to play and use it. If no diminished scale contains all the notes of your chord, pick another type of scale.

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In a strict sense, the diminished scale is the whole-half scale, because that's the scale you want to use over a diminished chord. It has all the notes of the diminished chord and all notes a whole step above those chord tones. Since these extra notes are a whole step above the chord tones they are no avoid notes.

If you used the half-whole scale over a diminished chord, you would also have all chord tones, but in addition you'd get four notes a half step above each chord tone. Those four notes would be dissonant in an undesirable way (i.e., they'd be avoid notes).

Having said that, it is indeed common to call both scales (whole-half and half-whole) diminished scale, so it's important to make sure which one is meant. Of course, they are modes of each other.

The half-whole scale is the one you want to use over a dominant seventh chord. It has all the chord tones and the b9, #9 and 13.

Note that the upper structure of a V7(b9) chord is just a diminished chord. E.g., G7(b9) is B diminished with a G in the bass:

G7(b9): G - B - D - F - Ab

Bdim7: B - D - F - Ab

Over the Bdim7 chord you'd use the B whole-half scale, and over G7(b9) you'd use the G half-whole scale. This makes sense because these scales are of course identical:

B w-h: B C# D E F G Ab Bb

G h-w: G Ab Bb B C# D E F

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One way to see and use a diminished scale is as a combination of two dim7 chords.

As a starting point, one way to see and use one dim7 chord is as a dominant chord, and its "mount points" are on the third and seventh of the dominant seventh. For example if you have a G7, you take its third, B, and put a dim7 there. Or you could take the G# - a semitone above the root - and place your dim7 there. It's the same thing, because dim7 is completely symmetric.

This overlaying of a dim7 on a dominant seventh is quite standard jazz stuff. For example, G7 <=> Bdim7 (or Fdim7 or G#dim7 or Ddim7) ... But if you add Gdim7 as well, you get the G half-whole diminished scale.

  • Gdim7 + G#dim7 = G half-whole diminished scale
  • ... and it works as substitute for a G7 dominant chord.

It might be easier to remember, if you notice that the G half-whole diminished scale contains all of the nice colorful notes: root (G), major third (B), minor third (Bb), tritone (C#), seventh (F). And of course G# which is a colorful and bitterly melodic addition to a dominant. However it does not contain A, which sounds more like easy-listening, elevatory, mellow, soothing when added to a G. (My subjective opinion)

In addition to the dim7 chords, the half-whole diminished scale has ingredients for more weird/interesting/fun chords that can be used as a dominant. For example, G7 <=> E/G or C#/G.

Check out this incredible "E7" chord, which consists of various things taken from the E half-whole diminished scale:

It's like one of those ambiguous repeating patterns, "what do you see in this picture" ... well, depending on how you look at it, you might see Fdim7, Bb major, Bb13-9, E7+9, G7, Gdim7?

And because it's symmetric, that thing should work not only as an E7, but as a G7, Bb7 and C#7.

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