- A major 9th chord implies the presence of the preceding 1st, 3rd, 5th, 7th, before the added 9th.
- This could also be written as an Amaj7 with an added 9th.
- In the 1st position chord, the 3rd (C#) is omitted... this is a particular voicing of the major 9th chord. This could also be classed as a maj7sus2 chord, in this case Amaj7sus2. The chord formula is 1-2-5-7 = A-B-E-G# (notes in the first position). Amaj9 is almost identical to Amaj7sus2 except the 9th is played an octave lower (9 - 7 = 2), and the 3rd is omitted. This voicing is quite common with 9th chords.
- A-major-ninth chords: You tend to find all types of 9th chords in alternate styles of music, especially jazz music where the use of extended chords and compound intervals are prevalent.
- Standard keys using the A major 9 chord: A/F#m and E/C#m. Both sets of scales share the same notes, i.e., A Major and F# minor share the same notes, as do E major and C#minor (F#m is the relative minor of A major, and C#m is the relative minor of E major).
- Amaj9 can therefore be used as a usable chord in any of the above chord progressions which means in this example, chords that utilize notes belonging to the A Major Scale (A-B-C#-D-E-F#-G#), and E Major Scale (E-F#-G#-A-B-C#-D#). Amaj9 meets the criteria (A - C# - E - G# - B)... this also includes the relative minor keys of F#m and C#m.