A♭ major · Tritone substitution
Tritone substitutions in A flat major
Every dominant in A♭ major, and its substitute
- V7subV7
B♭♭7 substitutes for E♭7, the dominant of A♭ major. They share the same tritone, so the bass can fall a semitone instead of a fifth. Shared notes: G and D♭ in E♭7, A♭♭ and D♭ in B♭♭7.
- F7V7/iisubV7/ii
C♭7 substitutes for F7, the dominant of B♭ minor. They share the same tritone, so the bass can fall a semitone instead of a fifth. Shared notes: A and E♭ in F7, B♭♭ and E♭ in C♭7.
- G7V7/iiiCmsubV7/iiiCm
D♭7 substitutes for G7, the dominant of C minor. They share the same tritone, so the bass can fall a semitone instead of a fifth. Shared notes: B and F in G7, C♭ and F in D♭7.
- V7/IVD7subV7/IV
D7 substitutes for A♭7, the dominant of D♭ major. They share the same tritone, so the bass can fall a semitone instead of a fifth. Shared notes: C and G♭ in A♭7, C and F♯ in D7.
- V7/VsubV7/V
F♭7 substitutes for B♭7, the dominant of E♭ major. They share the same tritone, so the bass can fall a semitone instead of a fifth. Shared notes: D and A♭ in B♭7, E♭♭ and A♭ in F♭7.
- C7V7/viFmsubV7/viFm
G♭7 substitutes for C7, the dominant of F minor. They share the same tritone, so the bass can fall a semitone instead of a fifth. Shared notes: E and B♭ in C7, F♭ and B♭ in G♭7.
Why the substitute works
What makes a dominant seventh want to resolve is the tritone between its third and its seventh. Move the root a tritone and that interval is still there, with its two notes swapped: the third becomes the seventh and the seventh becomes the third. So the substitute pulls to the same place, and the bass slides down a semitone to get there.
Play the two buttons in each row one after the other. Same arrival, different road.