Diminished Chords
Jazz Harmony based on Stacked Minor Thirds
Diminished chords are labeled either with a dim suffix ( ex. Bdim) or with a small circle (B°) to the top right of the chord. Musicians must be careful not to confuse this with the half diminished synbol where the circle is bisected by a line.
Diminshed chords occur as seventh chords with four chord tones. They produce an eerie, unstable sound that tends to move toward a more stable chord.
Building the Chord
Of all seventh chords, diminished chords are the smallest. They are comprised of nothing more than four minor thirds stacked upon each other. The diminished triad, like the half diminished, occurs on the seventh step of the major diatonic scale and on the second step of the minor scale. In C major B is a diminished triad: B D F ( notice that there is a minor third between each of these notes).
Similarly, in A minor B is also diminished. As per jazz convention, most chords are played as sevenths. This is what differentiates diminished from half diminished. B half diminished is: B D F A whereas B diminished is: B D F Ab. Notice that A is a minor 7th from B while Ab is one half step lower. This is the diminished seventh. So, the diminished doesn't occur naturally. Instead, a chord must be altered.
Moveable Chords
Due to the four minor thirds in the chord, diminished shapes repeat every minor third. For example: B dim is the same as D dim, F dim and Ab dim. They are exactly the same chord. The only difference is the voicings used. This gives them an incredibly useful function. They can be moved around and superimposed to give the music color.
Diminished chords also exist in another form, as 7b9 chords. Take G7b9: G B D F Ab. While all of the chord intervals are present in this spelling it is common practice to omit certain intervals. The third and the seventh and flat ninth are what define the chord so they must be retained. Keeping the fifth and dropping the root produces a diminshed seventh: B D F Ab. Any of these chord tones can be played over a G7 chord.
The Diminished Scale
This scale is often referred to as half-whole or whole-half, depending on where it is started. A diminished contains the notes A B C D Eb F Gb Ab. Notice that A-B (whole step), B-C (half step), C-D (whole), D-Eb (half) and so forth. The half- whole is the same principal only starting on a note followed by another a half step away. In the A diminished scale, starting on B would produce a half-whole scale.
As with chords, the different chord tones can be used as starting points for the scale. For G diminished it is possible to play diminished scales on G Bb Db E. All the notes of the four scales are all the same:
G A Bb C Db Eb Fb Gb
It is easy to see the vast combinations which are possible when dealing with just a single diminshed chord.
diminished chords
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