Diminished 7th Chord = PORTAL to 8 Tonalities

Diminished 7th chords (aka fully diminished chords) are symmetrical — any note can be considered the root note. They can resolve up a half step to a major or minor chord, or down a whole step to a major or minor chord.

Since there are 4 potential roots, this leaves us with 8 places we can modulate to from any given diminished 7th chord. In this video I explain this concept, then demonstrate how I wrote a piece of music using this same principle.

What You'll Learn

• Why diminished 7th chords are symmetrical
• How to resolve dim7 chords to major or minor
• Using dim7 as a modulation device to 8 different tonalities
• Scales to play over diminished chords (arpeggio, half-whole scale)

Skip to 08:07 to hear the original composition "OCTERMINUS" that demonstrates these concepts in action.

A Note on Enharmonic Spelling

A dim7 chord is constructed as root, ♭3, ♭5, ♭♭7. We're supposed to respect the musical alphabet — the 7th of C is B, the ♭7 is B♭, and the ♭♭7 is B♭♭. However, in the context of this lesson, it's easier to think of these notes by their simpler enharmonic equivalents (like calling B♭♭ just "A") when figuring out where to modulate next.

For a deeper dive into diminished chords and their role in harmony, check out Chapter 14: The Diminished Seventh Chord in the Chord Progression Codex.