A6 is A, C#, E and F# — with a major sixth added on top.
It sounds warm, and finished without being sweet. It closes a tune as firmly as the triad does but without the maj7’s shine, which is why so many standards end on one.
Tonic — an ending chord.
Also written Amaj6, AM6 or A major 6.
Alternate A6 with G#dim7 and the pair always sounds smooth: that diminished chord is the V7♭9 with its root left out, so the two chords are really I and V. Harmonising a melody this way puts the sixth chord under its own notes and the diminished chord between them.
Listen for: Every voice steps to its neighbour, a half or a whole step down, and back. Nothing leaps.
Heard in“Softly, as in a Morning Sunrise” (the same device on a minor sixth)
The line cliché works on a major chord too, though the minor form is far more common: hold A and walk one voice down from the root, a half step at a time. A6 is the last step, where the seventh has dropped to the sixth.
Listen for: Only one note moves: root, major seventh, flat seventh, sixth.
A6 can replace the major seventh as the home chord at the end of a ii–V–I.
In which keys. Every note of A6 belongs to C# minor, D major, E major, F# minor, A major and B minor.
Every note of A6 is in A major pentatonic, A major, A mixolydian, A lydian and A lydian dominant.
Each of those is a page: the scale across the neck, and the chords it harmonises into — which is where A6 sits in it. Every scale.
Change one note of A6 and you have (drop the sixth), (the sixth becomes the major seventh), (the major third becomes the minor third), (the sixth becomes the ninth), (add the ninth) or (the sixth becomes the flat seventh).
A6 is a major chord — root, major third, fifth. Major chords on every root.
The common shapes and the derived voicings come from different places, and both are explained in how this site is built.
Shows each chord the way this style would voice it, and marks which of its alternatives belong to the idiom.