Bdim7

Bdim7 is a four-note diminished seventh chord built on the note B. It consists of the pitches B, D, F, and Ab (enharmonic with G#), formed by stacking minor thirds. The chord is a fully diminished seventh, meaning all three successive intervals are minor thirds, giving it a symmetrical interval structure.

In functional harmony, Bdim7 commonly serves as the leading-tone seventh chord of C major and C minor (vii°7 of C). Its role is to create a strong pull to the tonic, with B resolving up to C and the other voices typically moving to stepwise targets within the C major or C minor harmony. Because it is fully diminished, the chord can be voiced in any of its four inversions: B–D–F–Ab, D–F–Ab–B, F–Ab–B–D, or Ab–B–D–F.

Culturally, Bdim7 is used beyond classical tonality as a color or tension chord in jazz and other modern music. It can function as a chromatic approach to tonic or act as a transient sonority that heightens resolution to C major or C minor. Enharmonic spelling allows it to be connected to other keys or chord progressions, sometimes serving as a pivot in modulation or a voice-leading device that emphasizes chromatic movement.