A9

Q: What notes are in the A9 chord?

The A9 chord (A 9th) contains: A, C#, E, G, B. Its interval structure is shown above in the Theory section.

Q: How do I build A9 on the keyboard?

Take the root and add the remaining chord tones following the interval formula. The highlight shows chord content, while the inversion control changes which chord tone is in the bass.

Q: Which keys is A9 found in?

The chord acts as a diatonic degree in several keys — they are marked on the circle of fifths in the "Harmonic context" block.

Q: What can I substitute for A9?

A substitution depends on harmonic function and voice leading, not only on shared tones. Computed options appear in the "Substitutions" block and should be checked in context.

A 9th

Octaves

Musical context

ChordA majorTriad

ChordA9A 9th

ArpeggioA majorBroken triad

ScaleA major7 notes

KeyA majorMajor key

ProgressionPop axisSequence

How the chord relates to the scale, mode, key and progression.

Theory

General info

Full name: A 9th
Symbol: A9
Root: A
Quality: 9th

Chord notes

1Aroot

3C#major 3rd

5Eperfect 5th

b7Gminor 7th

2Bmajor 2nd

Functions & resolutions

Typical function in key: VDominant (V)D major
Stability / tension: High tension — requires resolution
Most common resolutions: DD Major BmB Minor
Unstable degrees: 3C#
4D
resolves up to the resolution tonic
6F#
b7G
resolves down to the tonic 3rd
Main resolution: A9source
DD Major
Dominant 7th A7 naturally resolves up a 4th to D. It is the tritone between the chord's 3rd and 7th that creates this pull.
Other resolutions: A9source
Deceptive resolution
BmB Minor
Instead of the tonic, the dominant resolves to the vi degree. Creates surprise and is often used to extend a musical phrase.
A9source
Modal resolution
GG Major
In rock and blues, the dominant often moves to bVII or IV instead of the tonic, creating a modal flavor.
A9source
Jazz reharmonization
D#7D# Dominant 7
Tritone substitution: A7 can be replaced by D#7 (a tritone away). Both chords share the same tritone between the 3rd and 7th, resolving to the same tonic.
A9source
Functional resolution
Asus4A Sus4
The dominant can resolve beyond the tonic: moving to IV (subdominant) or to a suspension (sus4) are common alternatives in pop and folk music.

Substitutions

Tritone substitution: Eb7Eb Dominant 7

Features

Character: Dominant, with a minor 7th and major 9th
Characteristic interval: 9th
Description: The major 3rd and minor 7th form a dominant core, while the major 9th adds a diatonic extension. The dominant tritone preserves directed tension toward resolution.
Application: V9–I in jazz
Funk and soul
Blues harmony

Voicing & structure

Root position

v1A(A4)Bass

root

v2C#(C#5)M3from A

v3E(E5)m3from C#

v4G(G5)m3from E

v5B(B5)M3from G

Harmony

Compatible scales

All chord tones are contained in these scales — use them for improvisation.

ScaleC# Locrian ScaleC# Altered (super Locrian)ScaleE Dorian ScaleE Melodic minor ScaleE Neapolitan major ScaleG Lydian ScaleG Lydian augmented ScaleA Mixolydian ScaleA Mixolydian ♭6 ScaleB Aeolian (natural minor)

This chord on guitar 🎸

See how A9 looks on guitar.

Explore

Circle of fifths

Highlighted major keys contain this chord among their diatonic harmonies.

Relative key: F#mF# minor
Dominant: EE major
Subdominant: DD major
Key signature: 3 sharps (F#, C#, G#)

What to learn next

ScaleA MixolydianScale to improvise over this chord ChordA Dominant 7A nearby chord on the same root — compare the sound PracticeChord trainerLock the fingering into muscle memory ProgressionChord progressionsHow this chord works inside real progressions ChordA Major 9Another related chord to practise

Recommended for you

A Dominant 7A chord that sounds close

A Major 9A chord that sounds close

A Minor 9A chord that sounds close

A MixolydianA scale related to this chord

A Chromatic scaleA scale related to this chord

Practice

Keyboard Trainer

Reinforce it in practice — play and name notes on the interactive keyboard.

Open Trainer

Test yourself

(Press any key to start)

What notes are in the A9 chord?

How do I build A9 on the keyboard?

Which keys is A9 found in?

What can I substitute for A9?

A9