A9 A dominant ninth chord
- Notes
- A C# E G B
- Formula
- 1 3 5 b7 9
- Semitones
- 0 4 7 10 14 above the root
- Other symbols
- Adom9
A to C# is a major third (4 semitones), C# to E is a minor third (3 semitones), E to G is a minor third (3 semitones), G to B is a major third (4 semitones). A dominant seventh (A7) with the ninth, B, on top. Guitarists usually leave out the fifth, E; the chord still reads as A9 while the third C# and seventh G are there.
A9 on the piano
Root position from A4: A4, C#5, E5, G5, B5. Middle C is C4.
A9 on the guitar
Standard tuning (E A D G B E). Strings run low E on the left to high e on the right, frets downwards; × is a muted string, ○ an open string, and each dot shows the note it sounds, with the root in blue-green. Every shape below has A as its lowest note.
5 7 5 6 5 7 (low E to high e)
Sounds A2 E3 G3 C#4 E4 B4
x 12 11 12 12 12 (low E to high e)
Sounds A3 C#4 G4 B4 E5
The E-shape and A-shape grips are movable: an E-shape chord's root is the note under your first finger on the low E string, an A-shape chord's root is the note on the A string. Slide the same grip up or down to play dominant ninth chords on other roots.
Inversions of A9
An inversion puts a note other than the root in the bass. The name is what semicord's chord finder calls those notes played bottom to top; a slash name like C/E means a C chord with E in the bass.
| Position | Notes, bass first | Named | Listen |
|---|---|---|---|
| Root position | A C# E G B | A9 | |
| 1st inversion | C# E G B A | A9/C# | |
| 2nd inversion | E G B A C# | A9/E | |
| 3rd inversion | G B A C# E | A9/G | |
| 4th inversion | B A C# E G | A7/B (also read as A9/B) |
Where A9 fits
A9 is V9 in D major. It resolves like A7. In funk and blues it is also played as I9, IV9 and V9 of a twelve-bar blues, with no pull to resolve at all. Without the root, its upper four notes C# E G B are C#m7b5, which is why pianists who leave the root to the bass player grab that shape.