About this issue
Why this chart.
Diminished and augmented chords are the spice of harmony. You won't see them in pop verses, but they're everywhere in jazz turnarounds, classical cadences, and the bridge of any song that wants to feel unsettled or dreamy.
Diminished triads (1-♭3-♭5) sound tense and unstable. The diminished 7th (1-♭3-♭5-♭♭7) is symmetrical — every note is a minor third apart — which means a single shape produces four different chords by inversion. That makes diminished sevenths slippery in the best way: jazz musicians use them as passing chords in countless contexts.
Augmented triads (1-3-♯5) feel suspended in midair. The whole-tone scale lives inside them. Bowie's 'Space Oddity' opens with augmented harmony precisely because it sounds like floating.
How to use it
Treat diminished chords as transitional — they almost always resolve to a chord a half-step higher or lower. Augmented chords almost always resolve to a chord with a common tone. Don't park on either for too long; use them as connectors.