V7b9

V7b9 is a dominant seventh chord with a lowered ninth. It is built on the fifth scale degree of a key and includes the notes of a standard V7 chord plus a flat ninth above the root. For example, in the key of C major, the V chord is G, so G7b9 consists of G–B–D–F–Ab.

Functionally, V7b9 serves as a dominant with heightened tension that aims to resolve to the tonic (I or i). The added flat ninth intensifies the dissonance and strengthens the pull toward the next chord, often producing a more dramatic cadence. It is common in classical harmony as well as in jazz, where it appears as part of the broader family of altered dominant chords (V7alt) and is used to create chromatic voice-leading and rhythmic variety.

Voice leading for V7b9 typically emphasizes resolving the chord tones toward the tones of the tonic. The third of the V (the leading-tone to the I harmony) tends to move to the tonic note, the seventh of the V tends to resolve downward, and the flat ninth (the lowered ninth above the root) typically resolves upward by a semitone to a close, or otherwise moves to a consonant neighboring tone, depending on the context. The root of the V usually resolves to the tonic as part of the cadence.

Variants of the chord may include additional alterations such as b5 or #5, and in jazz notation it is often described as V7alt. In minor keys, the same concept applies with the appropriate scale-degree adjustments, e.g., E7b9 in A minor.