Chords
Half-diminished chord (m7♭5)
A half-diminished chord (m7♭5 or ø) is a diminished triad with a minor seventh added: Bm7♭5 = B D F A. It sets up the dominant in minor keys.
What is a half-diminished chord?
The half-diminished chord is the seventh chord with the formula 1 ♭3 ♭5 ♭7: a diminished chord (1 ♭3 ♭5) plus a minor seventh. Bm7♭5 = B D F A, Em7♭5 = E G B♭ D, F♯m7♭5 = F♯ A C E.
Symbols: m7♭5, ø or ø7. You can also think of it as an m7 chord with its fifth lowered by a semitone. It sounds dark and suspended, less aggressive than a fully diminished chord.
Why is it called "half" diminished?
Because only the triad is diminished. Compare it with the diminished seventh:
| Chord | Formula | Notes on B |
|---|---|---|
| Bm7♭5 (Bø) | 1 ♭3 ♭5 ♭7 | B D F A |
| Bdim7 (B°7) | 1 ♭3 ♭5 ♭♭7 | B D F A♭ |
The dim7 is "fully" diminished: its seventh is diminished too (A♭). The half-diminished keeps a minor seventh (A). Just one note separates them.
How do you play an m7♭5 chord on guitar?
Shapes from low E to high E (x = string not played):
- Bm7♭5, root on the 5th string:
x2323x(B F A D). - Bm7♭5, half-open:
x20201(B D A B F). - F♯m7♭5, root on the 6th string:
2x221x(F♯ E A C). - Em7♭5:
x7878x(E B♭ D G). Am7♭5:5x554x(A G C E♭).
The x2323x and 2x221x shapes are movable: slide them to reach any key. If you find another shape, the chord identifier will tell you whether it is an m7♭5 or an inverted m6.
Where is the half-diminished chord used?
- In major keys, on the 7th degree: Bm7♭5 in C. Its scale is the Locrian mode (B C D E F G A).
- In minor keys, on the 2nd degree: it opens the minor ii-V-I. In A minor: Bm7♭5, E7, Am.
Exercise in D minor, staying between frets 5 and 8: Em7♭5 x7878x, A7 5x565x, Dm x57765. The B♭ of Em7♭5 falls to A, then the C♯ of A7 rises to D. Play it slowly, two bars per chord, then move it to A minor with Bm7♭5 x2323x, E7 020100, Am x02210.
Common mistakes with half-diminished chords
- Mixing up ø and °: Bø = B D F A, B° = B D F (or B D F A♭ on jazz charts).
- Treating it as a plain m7: playing F♯ over Bm7♭5 (a perfect fifth) contradicts the chord. The ♭5 is what defines it.
- Ignoring equivalents: Bm7♭5 has the same notes as Dm6 (D F A B). On a chart that says Dm6, you can play a Bm7♭5 shape.
Key takeaways
- Formula: 1 ♭3 ♭5 ♭7 (Bm7♭5 = B D F A), symbol ø.
- viiø7 in major keys, iiø7 in minor keys.
- Core shapes:
x2323x(5th string) and2x221x(6th string). - It opens the minor ii-V-i: Bm7♭5, E7, Am.
Frequently asked questions
What is the difference between m7♭5 and dim7?
The seventh: minor in m7♭5 (Bm7♭5 = B D F A), diminished in dim7 (Bdim7 = B D F A♭). The dim7 is symmetrical and tenser, while the m7♭5 is darker and more stable.
What scale do you play over a half-diminished chord?
The Locrian mode of the root: over Bm7♭5, B C D E F G A. Jazz players also use Locrian ♮2 (B C♯ D E F G A), a mode of the melodic minor scale, which softens the minor second.
How are Bm7♭5 and G9 related?
G9 = G B D F A, and Bm7♭5 = B D F A. So Bm7♭5 is a G9 without its root. If a bass player plays G, your Bm7♭5 x2323x sounds like G9.
Related terms
Practise in the workshop
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