A dominant ninth
How to play A9 — Dominant ninth
A9 (Dominant ninth)A · C♯ · E · G · B
Guitar samples: Acoustic guitar — University of Iowa (via tonejs-instruments, CC-BY 3.0)
A dominant ninth — notes and structure
The A9 chord is a dominant seventh with the ninth added — funky and bluesy.
The A9 dominant ninth consists of the notes A, C♯, E, G, B. Its interval structure is R–3–5–7–9 — the root, then each chord tone stacked above it. This is the same chord you see in the interactive finder above, drawn on the guitar fretboard with the root circled and every chord tone labelled.
A9 stacks a major third (C♯), a perfect fifth (E), a minor seventh (G) and a ninth (B) above the root A.
The finder shows 2 ways to play A9 — an open-position shape reaching up to the 5th fret. 1 of them use a barre.
What key is A9 in?
Every note of A9 belongs to the scales below, so the chord sounds at home in each of these keys — the roman numeral is the degree it sits on.
- D major — the V chord
- B minor — the VII chord
Chords that go with A9
In D major, the chords built on the first, fourth and fifth degrees carry most songs — put A9 next to these:
Frequently asked questions
- What notes are in the A dominant ninth chord?
- The A9 chord contains the notes A, C♯, E, G, B. It is a dominant seventh with the ninth added — funky and bluesy.
- How many ways can you play A9 on guitar?
- 2 voicings are shown on this page — from open position up the neck — each with its own fingering diagram and audio.
- Is A9 a hard chord to play?
- Some voicings use a barre, which takes practice, but the chord is very playable once that shape is comfortable.
- What key does A9 belong to?
- A9 fits D major (where it is the V chord), B minor (where it is the VII chord) — every note of the chord is in those scales.