A nine chordA9

Built from

• Aroot
• C♯major 3rd
• E5th
• Gflat 7th
• B9th

A dominant 7 with a 9th stacked on top: still restless, but richer.

Hear it in a progression

• ii–V–I

  The backbone of jazz. In D major.

  Capo and transpose

  1. Em7ii7
  2. A9V7
  3. Dmaj7Imaj7
  4. Dmaj7Imaj7

• Blues opening

  The first four bars of a twelve-bar blues. In A major.

  Capo and transpose

  1. A9I9
  2. D7IV7
  3. A9I9
  4. A9I9

Where it goes next

Thinking in D major, where it is the V7 chord.

• Dmaj7

  Imaj7. The strongest pull in music: tension resolving home.

• Bm7

  vi7. The fake-out: you expect home, you get the relative minor.

Sounds close

• Cmaj7

  Shares 3 of its notes. Both have E, G and B.

• C♯m7

  Shares 3 of its notes. Both have C♯, E and B.

• C♯dim7

  Shares 3 of its notes. Both have C♯, E and G.

• Em7

  Shares 3 of its notes. Both have E, G and B.

Scales that fit

Notes you can play over this chord, simplest first.

• A minor pentatonic
• A blues
• A mixolydian

Keys it lives in

• D majoras V7
• B minoras VII7