Substitutions
Swapping a chord for another that does the same job, from diatonic substitution to the tritone substitute and the backdoor.
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Content under musical review. It may contain inaccuracies.
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Swapping a chord for another that does the same job, from diatonic substitution to the tritone substitute and the backdoor.
Advanced
To substitute a chord is to replace it with another that does the same job with a different colour. The basic idea: if two chords share the important notes, your ear accepts one in place of the other. Substitutions are the main tool of reharmonization, widely used in jazz, bossa nova and pop arranging.
G7 and D♭7, played with just root, third and seventh. Notice that the top two notes are the same (spelled differently):
Both resolve to the tonic. Compare a regular ii–V–I with its substituted version:
ii – V7 – Imaj7 ii – bII7 – Imaj7In the second, the bass walks down by half steps: D, D♭, C.
| Substitution | Original | Substitute | Why it works |
|---|---|---|---|
| Diatonic (tonic) | C | Am, Em | two shared notes |
| Diatonic (predominant) | F | Dm | shared F and A |
| Tritone | G7 | D♭7 | same tritone: B/C♭ and F |
| Diminished | G7 | Bdim7 | a rootless G7♭9 |
| Backdoor | G7 | B♭7 | bVII7 from the parallel minor |
The tritone substitute sits six half steps from the original dominant. Its seventh (C♭) is enharmonic with the third of G7 (B), and its third (F) is the seventh of G7.
String 6, Fret 1: F2 · 3 · Third
Try the backdoor cadence, which reaches the tonic from bVII7 instead of V7:
iv7 – bVII7 – Imaj7And a reharmonization of I – vi – ii – V with tritone substitutes:
Imaj7 – bIII7 – ii7 – bII7 – Imaj7E♭7 replaces A7 (V7/ii), and D♭7 replaces G7.
When improvising over a tritone substitute, D♭ lydian dominant contains the same notes as G altered. It's the same sound seen from two roots.
Take a simple progression and change one chord at a time: first a diatonic substitution, then a secondary dominant before a minor chord, and finally a tritone substitute. If the melody clashes with the new chord (say, the melody has C over D♭7), choose another option: the melody comes first.
Ear & improvisationTarget tonesImprovise over a backing track aiming at a specific tone of each chord.Levine devotes a chapter to the tritone substitute: because the tritone splits the octave into two equal halves, two dominants a tritone apart share the same third–seventh pair with the roles swapped. The same principle lets you replace a whole ii–V: A♭m7 – D♭7 instead of Dm7 – G7.
In classical theory, the augmented sixth chord (in C: A♭, C, E♭, F♯) resolves to V and enharmonically contains an A♭7, the tritone substitute of D7 (V/V). Kostka and Payne study it as one of the chromatic predominant chords.