Bm7b5

Bm7b5, written as Bø7 in shorthand, is a half-diminished seventh chord built on the note B. It consists of the notes B, D, F, and A: a root, a minor third (D), a diminished fifth (F), and a minor seventh (A). The chord can also be described as a diminished triad B–D–F with a minor seventh added.

Function and use: In major keys, Bm7b5 is the viiø7 of C and acts as a leading-tone harmony that commonly resolves to C major (or C minor). In minor keys, it often appears as the iiø7 in a iiø7–V7–I progression in the key of A minor (Bø7–E7–Am). Jazz practice frequently places Bm7b5 before a V7, providing smooth voice-leading into the dominant. It is also used as a passing or substitute harmony in various keys.

Voicing and notation: The chord is notated Bm7b5 or Bø7. It can be voiced in all inversions: B–D–F–A (root position), D–F–A–B, F–A–B–D, or A–B–D–F. The half-diminished character comes from the diminished triad with a minor seventh; it should be distinguished from Bdim7 (B–D–F–Ab), which contains a diminished seventh.

Summary: Bm7b5 is a versatile half-diminished seventh chord used in both classical and jazz contexts, often functioning as a predominant harmony that leads to a tonic or dominant harmony, with common appearances in iiø7–V7–I progressions in minor keys and as a leading-tone chord in major keys.