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Not all non-diatonic notes of all modes have appropriate parallel
chords that can be borrowed. Due to this, many of them were chosen
through less ‘scientific’ means.
A combination of choices between ‘most harmonically relevant,’ i.e.
choosing chord qualities that contained the most chord tones diatonic to
the mode, and more simply, what sounded best.
The full breakdown of what chord tones are included chromatically for
each mode are as follows:
Ionian Modes
Ionian
Dorian
Phrygian