Dominant 7th #9
7#9
0 - 4 - 7 - 10 - 15Hendrix chord
About Dominant 7th #9
A dominant seventh sharp nine chord is a dominant with a raised ninth — in C that is C, E, G, B♭ and D♯, written C7♯9. The raised ninth is the same pitch as a minor third, so the chord contains a major third and a minor third at once, and that contradiction is precisely the sound the blues has been built on for a century.
Notes and formula
The formula is 1 – 3 – 5 – ♭7 – ♯9, or 0 – 4 – 7 – 10 – 15 in semitones. The raised ninth sits fifteen semitones above the root, an octave plus a minor third.
Spelling it as a raised ninth rather than a flattened tenth is not pedantry: it keeps the chord readable as a dominant with one alteration, rather than as a chord with two thirds, which is what it sounds like.
Why two thirds sound right here
Blues melody has always used a flattened third over a major-third harmony — that clash is the blue note, and singers and guitarists produce it constantly without naming it.
This chord writes the clash into the harmony instead of leaving it to the melody. That is why it sounds familiar to listeners who have never heard the symbol: they have been hearing the interval since the first blues record they encountered.
How to play it
On guitar the movable form with the root on the fifth string is x–3–2–3–4–x, sounding C–E–B♭–D♯. On the sixth string the classic shape is 8–x–8–9–9–x with the ninth added above.
The shape is famous under one name in particular — the Hendrix chord — because Purple Haze opens on it and because the fingering falls naturally under an electric guitarist's hand.
Where you hear it
In blues-rock and funk as a standing chord rather than a passing one: the tension is a texture, and it can carry a whole riff.
In jazz it appears at the end of a phrase, resolving down a fifth like any dominant, and in big-band writing as the last chord before a shout chorus.
Against the flat nine
C7♭9 lowers the ninth and sounds urgent and classical. C7♯9 raises it and sounds gritty and modern. The two are alterations of the same degree in opposite directions and belong to different musical worlds.
Both resolve the same way. Choosing between them decides the genre of the bar, not its harmony.
Scales that contain it
The altered scale — the seventh mode of melodic minor — is the standard choice, and the half–whole diminished scale works too, adding a natural thirteenth the altered scale lacks.
Over a blues, players ignore both and use the minor pentatonic. The chord already contains the clash the scale would create, so nothing sounds wrong.
Frequently asked questions
What notes are in a C7♯9 chord?
C, E, G, B♭ and D♯. On guitar, x–3–2–3–4–x.
Is the sharp nine the same as a minor third?
The same pitch, a different function. Written as a raised ninth it is an alteration on top of a dominant chord; written as a minor third it would contradict the major third below it.
Why is it called the Hendrix chord?
Because Purple Haze opens on it and made the sound famous. The chord existed in jazz long before, but the name stuck to the electric-guitar voicing.