Module 14 — Diminished Chords in Practice
Diminished harmony looks mysterious at first because of symbols like:
B°, B°7, Bm7♭5 / Bø7
But once you separate those three things, diminished chords become extremely useful rather than intimidating.
The big idea is:
Diminished chords are tension machines. They are especially good at connecting two nearby chords, creating chromatic bass lines, and strongly pointing toward a destination.
14.1First, the three diminished-type chordsLet’s use B.14.2Start with B° → CYou already know:14.3B° is basically part of G7G7:14.4Leading-tone diminished chordThe note one semitone below the tonic is the leading tone.14.5Hear the same relationship in several keysPlay:14.6Why diminished triads sound unstableB°:14.7Fully diminished seventh makes it strongerNow play:14.8Why diminished seventh chords are specialLook at B°7:14.9The same physical notes can represent four diminished chordsTake:14.10Move a diminished chord up 3 semitonesPlay:14.11Why this matters physicallySuppose you know one shape:14.12B°7 → CFirst destination:14.13D°7 can point somewhere elseSame physical notes:14.14One diminished shape, four possible destinationsThe chord:14.15Don't worry about exotic spellings yetOn paper, composers may spell the same piano keys differently to make the harmonic function clear.14.16Passing diminished chordOne of the most useful practical applications:14.17What is C♯°7?Starting on C♯:14.18The passing-diminished formulaA very common pattern:14.19Another common one: ii → #ii°7 → iiiIn C:14.20Another: IV → #IV°7 → VIn C:14.21Diminished chord as chromatic glueSo one major role is:14.22Why it works so wellBecause each voice often moves by a semitone.14.23Diminished passing chords with inversionsYou do not have to play the diminished chord root in the bass.14.24Diminished chord can approach a chord from belowSuppose destination is:14.25Destination exerciseWant C?14.26Diminished versus dominantCompare:14.27A fascinating relationship: dominant ♭9Take G7♭9:14.28This gives you a practical trickIf bass plays G,14.29ExampleLH:14.30Dominant ♭9 contains a diminished chord on its 3rdGeneral rule:14.31E7♭9 → AmLH:14.32Diminished chords in minor keysIn A minor, the leading tone is G♯.14.33Half-diminished is differentDon't confuse that with:14.34Compare the twoIn A minor:14.35Hear both routesPlay:14.36Diminished chords can prolong a dominantAnother useful use:14.37Common jazz turnaroundTry:14.38Compare the two routesC → A7 → Dm14.39Diminished chord underneath a held melodySuppose melody holds E.14.40Diminished chords can sound old-fashioned, elegant, or dramaticStyle depends on context.14.41Diminished scale previewA fully diminished chord divides the octave symmetrically.14.42The diminished chord's real secretIt often looks complex on paper, but at the keyboard ask:14.43Practical voicing: B°7 → Cmaj7Try:14.44Practical voicing: C♯°7 → Dm7C♯°7:14.45That's why this progression sounds so inevitableC → C♯°7 → Dm714.46Turn an ordinary progression into a richer oneBasic:14.47Combine diminished and secondary dominantsTry:14.48A descending diminished useDiminished chords can also connect descending roots depending on inversion and context.14.49Diminished chord as a bridge to a remote keyBecause one °7 chord can be reinterpreted under four root names, it can act as a pivot.14.50Improvisation over a passing diminished chordSuppose:14.51Example melodic lineOver C:14.52Hear before namingPlay diminished seventh chords randomly.14.53Your diminished-chord toolkitFor now, you need four practical uses:•Homework for Module 14On B, play:•Module 14 mini-test1. What notes are in B°?