C7b5 guitar chord
Root, third and seventh: the guide tones fix the quality, so the fifth is dropped. That is what leaves a string free, so pick a tension to put on top.
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About C7b5 — shell voicings
C7b5 is C, E, Gb and Bb — C7 with the fifth lowered a semitone.
It sounds symmetrical and slightly unreal. The same four notes spell a 7♭5 a tritone away, which is exactly why one can stand in for the other.
C7b5 notes and formula
| C | E | Gb | Bb |
|---|---|---|---|
| 1 | 3 | ♭5 | ♭7 |
Altered dominant — and the chord that makes the tritone substitution work.
Also written C7(b5), C7-5 or C7♭5. The same chord either way; which spelling you meet depends on who wrote the chart.
How to play C7b5
Root, third and seventh. The third and seventh, the guide tones, are what make the chord major, minor or dominant, so the fifth can go: it says nothing the symbol needs.
Three notes means a spare string, which is the real point. Put a tension on it.
C7b5 has 5 of them, on strings 5-3-2-1, strings 6-4-3-2, the bottom four strings, the middle four strings and the top four strings, from the 2nd fret up to the 9th — all in one inversion, so the bass note never moves. The one to learn first is the C shape at the 2nd fret.
Start with xx2312 — down at the nut. None of the shapes for C7b5 uses an open string, so every one of them is movable; the lowest sits at the 1st fret. None of them needs a barre. Together they cover the neck from the 1st fret to the 12th.
| Frets | Where | Bass | Top | Hand |
|---|---|---|---|---|
| x12312 | 1st fret | Bb, 3rd inversion | Gb | all fretted |
| xx2312 | 1st fret | E, 1st inversion | Gb | all fretted |
| x3435x | 3rd fret | C, root position | E | all fretted |
| 8x8970 | 7th fret | C, root position | Gb | 1 open string |
| x-x-10-11-11-12 | 10th fret | C, root position | E | all fretted |
The same notes rebuilt from scratch give 14 drop 2, 9 drop 3 and 2 open string voicings, each on its own page.
Tensions. A shell of C7b5, root, third and seventh, leaves a string free, and the tones that belong over it are the b9 (Db), the 9 (D), the #9 (D#), the b13 (Ab) and the 13 (A).
How to use C7b5
C7b5 is a dominant with its tension raised, so it still points at F — harder than a plain seventh does, because the altered tones sit a semitone from where they are going.
Voice by voice, C7b5 → F. 3 voices move by a semitone, and one note is common to both chords.
| In C7b5 | Moves | In F |
|---|---|---|
| C, the root | stays where it is | C, the fifth |
| E, the major third | rises a semitone | F, the root |
| Gb, the flat fifth | falls a semitone | F, the root |
| Bb, the flat seventh | falls a semitone | A, the major third |
What to play over C7b5
Every note of C7b5 is in C whole tone, C lydian dominant, C altered and C half-whole diminished.
Chords near C7b5
Change one note of C7b5 and you have Cmaj7b5 (the flat seventh becomes a major seventh), Cm7b5 (the major third becomes a minor third), C7 (the flat fifth becomes a fifth), C7/G (the flat fifth becomes a fifth), Caug7 (the flat fifth becomes a sharp fifth) or C9b5 (add the ninth).
C7b5 is an altered chord — a dominant seventh with its fifth or ninth moved. Altered dominant chords on every root.
On C7b5’s sound and use this page follows Mark Levine, The Jazz Theory Book (Sher Music, 1995). The shapes and the derived voicings come from different places, and both are explained in where the chords and the theory come from.