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6.6.5Chords of the Major Scale + Chords of the Minor Scale = Circular Harmonic Scale
A while back, the triad chords built on the seven different notes of the diatonic scale were introduced as the seven harmonic degrees. Three of the triads were chords of the major scale and three were chords of the relative minor scale. And one was a diminished chord. These same chords, organized in a circle, form a circular harmonic scale (Figure 47 above). The major chords form a family of three on the right, the minor chords form another family of three on the left. (Isn’t that sweet?) The diminished chord (VIIº)—no doubt trained as an expert in family group dynamics and conflict resolution—appears to bridge the two families.
The next thing you might notice is that all but one of the intervals between the roots of the chords is five semitones apart (a fifth progression down, going clockwise; a fifth progression up, going counterclockwise). The exception is the interval between the root of the IV chord and the root of the VIIº chord (six semitones).
Later in this chapter, you’ll see how this little anomaly helps explain why composers have a hard time working with the Church modes (Dorian, Phrygian, Lydian, Mixolydian, Locrian) when it comes to constructing palatable-sounding chord progressions.