C#m7b5 Chord on Guitar
C#m7b5 = C# – E – G – B (Root, Minor 3rd, Tritone, Minor 7th)
C#m7b5 — also called C# half-diminished — occupies a specific and important harmonic niche as the standard ii chord in minor-key jazz progressions, the essential first link in a minor ii-V-i cadence. At the ninth fret, its E-shape barre voicing is one of the more physically involved shapes in this cluster, needing an extra reach for the flattened fifth beyond what a plain minor seventh chord requires.
The notes are C#, E, G, and B — root, minor third, diminished fifth, flat seventh — which makes it easy to confuse with a diminished seventh chord on paper, but the two are meaningfully different: a full diminished seventh flattens the seventh twice, while half-diminished flattens it only once, giving m7b5 a smoother, more functional sound suited to ii-V-i minor cadences rather than existing purely as unstable passing color. As ii in a minor key, C#m7b5 leads directly into a dominant chord, often altered, before resolving to the i.
Fingerings
Barre (9th fret)
How to Practice It
The diminished fifth demands a stretch beyond what the plain C#m7 shape asks for, similar to the reach the diminished triad needs but layered onto a fuller four-note chord, so isolating that finger placement before attempting the whole shape at tempo is worthwhile. Because this chord's real identity comes from its function within a ii-V-i progression, practicing it directly alongside the V and i chords it typically precedes builds a far more useful understanding than learning the shape in isolation.
Common Progressions
- C#m7b5 – F#7 – Bm (ii7b5 – V7 – i, a textbook minor ii-V-i)
- C#m7b5 – F#7b9 – Bm7 (a jazzier version with an altered dominant)
- C#m7b5 – F#7 – Bm6 (resolving the minor ii-V into a colored tonic)
- D#m7 – C#m7b5 – F#7 – Bm (a longer minor-key jazz turnaround)
FAQ
- What's the difference between C#m7b5 and C#dim7?
- Half-diminished flattens the seventh once, giving a flat seventh, while a full diminished seventh flattens it twice, giving an interval enharmonically the same as a major sixth — making dim7 the more symmetrical and unstable of the two.
- Why is C#m7b5 called 'half-diminished'?
- It shares the diminished triad's root, minor third, and flattened fifth, but uses a regular flat seventh rather than continuing the fully diminished stacking pattern.
- What's C#m7b5's most common harmonic role?
- It functions as the ii chord in minor-key ii-V-i progressions, an essential building block of jazz harmony in minor keys.
- Why does this chord need an extra stretch to finger?
- The flattened fifth sits a half step below the perfect fifth a plain C#m7 would use, demanding more precision and reach than the unaltered minor seventh chord asks for.
- Is C#m7b5 common outside jazz?
- It's much less common in rock and pop, appearing instead in more harmonically ambitious singer-songwriter and film-score writing that wants the specific tension of a minor-key ii chord.
- Does C#m7b5 ever substitute for a diminished seventh chord?
- Occasionally, since the two share three of their four notes, but they're not fully interchangeable — m7b5's smoother flat seventh gives it a more functional role than the fully diminished chord's.
- Why does a minor ii-V-i sound different from a major one even though the shapes are related?
- Swapping the ii chord's fifth down to diminished, and often altering the V chord's own upper structure, injects extra chromatic tension throughout the whole progression that a plain major-key ii-V-I never has, giving minor cadences their characteristically darker pull.
C#m7b5 on other instruments: C#m7b5 on Piano. Related: how chords are built, chord finder.