Stop 4 of 6
Substitutions
Tritone, diatonic and diminished substitutions.
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Stop 4 of 6
Tritone, diatonic and diminished substitutions.
A progression is like a route between two cities: you can take the motorway or the back roads with better views. Substitutions are those detours. You swap a chord for another that does the same job, so the ear reaches the same destination, but along a path with more colour, a more melodic bass or more tension. In this stop you'll meet the four substitutions used most in jazz and modern music.
Listen to two versions of the most famous ii–V–I. Only the middle chord changes:
The second version reaches Cmaj7 just as surely, but with a more sophisticated flavour. Focus on the bass: in the original it leaps (D – G – C); in the substituted one it falls by half steps.
How can D♭7, a chord so far from C major, do the job of G7? Look at their notes:
C♭ sounds the same as B: they are . So the two chords share the same two guide tones, the tritone B–F. In G7, B is the third and F the seventh; in D♭7 the roles swap. And that tritone is exactly what resolves to C: B rises to C and F falls to E.
This is : any dominant seventh chord can be replaced by the dominant whose root is a tritone (six semitones) away. On guitar it's even clearer. Play these two shells: the top two notes are identical, only the bass moves.
If you play D♭7 over a G bass, its notes are D♭ (the ♭5 or ♯11 of G), F (♭7), A♭ (♭9) and C♭ = B (3). In other words, D♭7 is a G7 with b9 and #11. That's why the scale that sounds best over D♭7, D♭ Lydian dominant, contains exactly the same notes as the G altered scale you'll see in the next stop.
The substitution works for secondary dominants too. A7 (V/ii) becomes E♭7, and the result is a bass that falls by half steps for several bars:
And the substitute can take its own related ii: A♭m7 – D♭7 – Cmaj7.
The gentlest way to substitute doesn't leave the key. Diatonic chords group into families by function, and members of a family share most of their notes:
| Function | Chords in C | Shared notes, for example |
|---|---|---|
| I, iii, vi | Cmaj7 and Am7 share C E G | |
| IV, ii | Fmaj7 and Dm7 share F A C | |
| V, viiø | G7 and Bm7♭5 share B D F |
With you swap a chord for a relative in its family. Hear a simple progression and a version with substitutes:
Look at the ending: replacing the final I with vi produces a . Diatonic substitution doesn't just add variety; it also lets you postpone the end of a phrase.
Play Cmaj7 and then Dm7. Between the two bass notes there's a gap: C → D. A chord fills it with a half step: C♯dim7.
The bass climbs by half steps: C, C♯, D, D♯, E. But there's something deeper. C♯dim7 has the notes C# E G Bb, exactly those of A7♭9 without its root. So the passing diminished is a disguised V/ii, which is why it resolves so well to Dm7. In the same way, D♯dim7 is B7♭9 without its root, the V/iii.
You already know the from modal interchange. Now you can see it as one more substitute for V7: Fm7 – B♭7 takes the place of Dm7 – G7. B♭7 shares the notes D and F with G7, and its A♭ is the b9 of G.
The last tool is the freest: the chromatic approach chord. Any chord can be preceded by another of the same type a half step above or below. It's pure : it has no tonal function, and the parallel motion of all the voices justifies it.
The four substitutions aren't interchangeable: each changes something different in the progression. This table helps you decide according to what you want to achieve:
| Substitution | What changes | Effect | Watch out for |
|---|---|---|---|
| Tritone | the dominant's root | chromatic bass, altered colour | the melody: the 5 of G is the b9 of Db |
| Diatonic | a chord for another in its family | variety without leaving the key | phrase endings: vi instead of I postpones the cadence |
| Passing diminished | adds a chord between two | bass rising or falling by half steps | tempo: very fast, it sounds like a stumble |
| Backdoor | V7 for iv7–bVII7 | soft, warm arrival | mixing it with a V7 just before, which cancels it |
| Chromatic approach | adds a parallel chord | a slide, a surprise | overuse: more than one per phrase sounds like an effect |
A good habit is to start with the gentlest (diatonic), then try the chromatic ones and keep only the one that best serves the song. Play the original progression, then the substituted one, and ask yourself: what does the music say now that it didn't before?
Here the melody makes the substitution shine: over D♭7 it sings G (♯11) and F (3), two notes that fit perfectly.
Goal: Alternate the original and the tritone-substituted ii–V–I for two minutes at 100 BPM without looking at the neck on the changes.
Goal: Play Cmaj7 – C#dim7 – Dm7 – D#dim7 – Em7 in quarter notes at 90 BPM with the chromatic bass clear on the fifth string.
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