Module 22 — Chord Substitution: Different Chords, Same Job
Reharmonization changes the harmonic path. Chord substitution is a more specific idea:
Replace a chord with another chord that can perform a similar function or preserve important notes and voice leading.
This is where jazz harmony starts to look much more flexible.
We’ll focus on:
- relative substitutes
- dominant substitutes
- tritone substitution
- backdoor dominant
- common-tone substitution
- chromatic approach substitutions
22.1Start with functional substitutionIn C major:22.2Relative substitutesC major:22.3Why substitutions workUsually for one or more of these reasons:22.4Dominant substitution begins with the tritoneTake:22.5G7 and D♭7 share the same dominant tensionG7 guide tones:22.6Hear itPlay:22.7Bass motion becomes chromaticOriginal:22.8Tritone substitution formulaA dominant chord can often be replaced by another dominant chord whose root is a tritone away.22.9Why exactly a tritone away?Because dominant 7 chords themselves contain a tritone between:22.10Practice the guide tones onlyPlay:22.11Tritone substitution in ii–V–IOriginal:22.12Hear both versionsVersion A:22.13A more colorful voicingTry:22.14Tritone substitution of secondary dominantsIn C:22.15Another exampleOriginal:22.16Descending dominant substitutionsA beautiful chain:22.17Tritone substitution is still dominant functionThis is important.22.18`subV`In analysis you may see:22.19Tritone substitution doesn't always fit the melodySuppose melody over G7 is:22.20Melody can become an extension automaticallyThis is often where tritone substitutions become exciting.22.21Dominant substitution with diminished harmonyWe already learned:22.22Compare three dominant approachesTo C:22.23Backdoor dominantNow another very useful jazz sound.22.24Where backdoor dominant comes fromThink of borrowed harmony from C minor.22.25Hear itPlay:22.26Compare three cadencesG7 → Cmaj722.27ii–backdoor–IBackdoor dominant is often prepared by its ii chord.22.28Compare with normal ii–V–INormal:22.29Why “backdoor”?The normal route into C is:22.30Backdoor dominant and melodySuppose melody is G.22.31Common-tone substitutionAnother substitution strategy:22.32One note, five harmonic identitiesHold E.22.33Common-tone chromatic substitutionHold G.22.34Common tones make remote chords sound less remoteThis is an important arranging principle.22.35Relative-major/minor substitutionA simple form of common-tone substitution.22.36Relative minor of IVFmaj7:22.37Seventh chords make relative substitutions even clearerTriads:22.38Dominant-family diminished substituteG7:22.39Chromatic approach dominantSuppose target is Cmaj7.22.40Chromatic dominant planingTry:22.41Tritone substitution creates chromatic ii–V bassNormal:22.42Add extensionsTry:22.43A simpler D♭7 voicingLH: D♭22.44The enharmonic spelling matters on paperFor D♭7, the seventh is theoretically:22.45Tritone-sub guide-tone reversalNormal G7:22.46Substitute secondary dominant in our standard progressionOriginal:22.47Don't substitute every dominantThe progression above is an experiment, not necessarily tasteful.22.48Backdoor after normal cadenceTry:22.49Backdoor instead of borrowed ivCompare:22.50Dominant substitute hierarchyTo resolve to C, you now have:22.51Learn them by emotional characterPlay all five.22.52Melody compatibility exerciseHold melody:22.53Another melody note: GHold G.22.54Substitution and bass lineSometimes you choose a substitution primarily for bass.22.55Substitution and inner voicesOr choose based on a middle voice.22.56Chord substitution is not mathematical equivalenceWhen we say:22.57Three questions before substitutingBefore replacing a chord, ask:22.58A practical substitution ladderTake:22.59Add melody to the ladderChoose a top melody:22.60Your substitution toolboxAt this stage, know these categories:•Homework for Module 22Memorize physically:•Module 22 mini-test1. What is chord substitution?