Many composers in the 20th and 21st centuries have made use of the reflective, or mirror, possibilities that all scales and chords possess.
For example, if we take an ascending Major (Ionian) scale we get the following intervals between its scale degrees:
T – T – ST – T – T – T – ST.
If we now take these same intervals but descend, we get the Phrygian mode
The reflective nature of scales, and modes, means that all major scale modes mirror other modes; the only exception is the Dorian mode which mirrors itself.
The possibilities for this are extensive and can be used with other scales such as the Pentatonic scale:
here, the ‘minor’ pentatonic scale, commonly used by guitarists, mirrors a ‘Scottish’ pentatonic scale.
or, exotic scales such as the Oriental scale, which mirrors the Hungarian minor scale.
or, we can mirror harmonised scales and modes
Notice, here it is both the vertical intervals of each chord and the intervals between scale degrees which are mirrored. For example, like all major chords, the initial major chord on the tonic of an ascending major scale is constructed by a minor third on top of a major third therefore, the initial chord of the descending mode is a minor chord: major third on top of a minor third.
Mirrored chords and scales can be used like any diatonic chord progression or scale set. The only difference is that the combination of sounds of both a scale and its mirror will create a bitonal or polytonal soundworld rather than the more familiar diatonic soundworld.