The diminished scale can be constructed simply by preceding each note of the diminished seventh chord with a note a semitone below. It follows that the diminished scale consists of two augmented triads a semitone apart. In this example each note of the C diminished seventh chord is preceded by a note a semitone below. This creates a symmetrical scale made up of alternating half-steps and whole-steps. Because the scale is symmetrical at the minor third, any motif or chord from the scale can be transposed up or down a minor third and remain within the scale.

Here is the C diminished scale. It can also be viewed as the Eb, Gb, or A diminished scale.

Here we have a four-note voicing which is used to harmonize the scale. Each voice follows a scalar line. Every other chord has the same intervallic shape as the voicings continue to replicate themselves in ascending minor thirds. An arpeggiated version of the same chord sequence follows in the second staff.
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This diagram shows how the diminished chord relates to the four dominant chords. Notice that the dominant chords are a minor third apart from each other.
The diminished scale, when following the whole-step/half-step pattern, relates to diminished chords, but when following a half-step/wholestep pattern, it relates to dominant chords. This means that the C diminished (whole-step/half-step) contains the same notes as B diminished (half-step/whole-step), which is sometimes called the “dominant diminished” scale.

Here is a chart that shows the function of each scale tone over the dominant chords.

Here are some practical fingerings for the diminished scale. This diminished scale fingering uses four notes per string.

This diminished line is based on major triads a minor third apart. Download example audio.

This diminished line outlines D/Eb, F/Gb, and Ab/A. Try this line over F7, D7, Ab7, or B7. Download example audio.

This lesson comes from:

Modern Jazz Concepts for Guitar