The A Add 9 chord is a four-note chord made up of A, C♯, E, and B. It is built from a root, major third, perfect fifth, and major ninth.
Construction
A Add 9 = Root + Major 3rd + Perfect 5th + Major 2nd = A · C♯ · E · B
| Note | Interval | Degree |
|---|---|---|
| A | Root | 1 |
| C♯ | Major 3rd | 3 |
| E | Perfect 5th | 5 |
| B | Major 2nd | 2 |
A Add 9 Inversions
| Position | Notes |
|---|---|
| Root Position | A – C♯ – E – B |
| 1st Inversion | C♯ – E – A – B |
| 2nd Inversion | E – A – B – C♯ |
| 3rd Inversion | A – B – C♯ – E |
Key Signature
A chord has no key signature of its own, but the A Add 9 is the tonic (I) chord of A Major, whose key signature has 3 sharps (F♯, C♯, G♯).
F♯C♯G♯
Order of sharps
Sharps are added to a key signature in a fixed order. Each new sharp key adds the next sharp on the list.
F♯C♯G♯D♯A♯E♯B♯
Mnemonic: Father Charles Goes Down And Ends Battle
Chords in the Key of A Major
These are the triads built on each degree of the A major scale:
Same Notes, Other Names
The notes A – C♯ – E – B aren’t exclusive to this chord. Depending on which note is the bass and how the chord functions, the same pitches also spell:
A Add 9 — Frequently Asked Questions
What is the A Add 9 chord on piano?
The A Add 9 chord contains the notes A – C♯ – E – B. On piano, play these notes together to sound the chord.
What notes are in the A Add 9 chord?
The A Add 9 chord (Aadd9) contains four notes: A (root), C# (major third), E (perfect fifth), and B (major ninth). No seventh — the ninth adds brightness to the triad.
How does Aadd9 differ from A9?
Aadd9 has no seventh. A9 includes the minor seventh (G). Aadd9 is bright and open; A9 is dominant and bluesy.
How is Aadd9 used in music?
Aadd9 substitutes for A Major in pop, rock, and country. A Major is one of the most common guitar keys, making Aadd9 a frequent voicing in acoustic arrangements.
What songs use add9 chords?
Add9 chords appear in Wonderwall (Oasis), Good Riddance (Green Day), and countless acoustic pop songs. Aadd9 is common in country and folk-rock.
How does Aadd9 differ from Asus2?
Both contain A and B. Aadd9 keeps C# (major third); Asus2 replaces it. Aadd9 is major with colour; Asus2 is ambiguous.
Can I substitute Aadd9 for A Major?
Yes — Aadd9 replaces A Major in most pop and acoustic contexts for added shimmer.