B♭ major · Tritone substitution
Tritone substitutions in B flat major
Every dominant in B♭ major, and its substitute
- F7V7subV7
C♭7 substitutes for F7, the dominant of B♭ major. 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/iiCmsubV7/iiCm
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.
- A7V7/iiiDmsubV7/iiiDm
E♭7 substitutes for A7, the dominant of D minor. They share the same tritone, so the bass can fall a semitone instead of a fifth. Shared notes: C♯ and G in A7, D♭ and G in E♭7.
- V7/IVE7subV7/IV
E7 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, D and G♯ in E7.
- C7V7/VFsubV7/VF
G♭7 substitutes for C7, the dominant of F major. 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.
- D7V7/viGmsubV7/viGm
A♭7 substitutes for D7, the dominant of G minor. They share the same tritone, so the bass can fall a semitone instead of a fifth. Shared notes: F♯ and C in D7, G♭ and C in A♭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.