C#maj9 is C#, E#, G#, B# and D# — with the ninth stacked above it.
It sounds a maj7 with more air in it. The ninth argues with nothing here, so it works anywhere a maj7 does.
Tonic — an extended resting chord.
Also written C#M9, C#Δ9, C#ma9 or C# major 9.
At the end of a jazz ii–V–I, C#maj9 is the usual landing rather than a bare major seventh. The top voice that was the ii’s ninth and the V’s thirteenth steps down onto the ninth.
Listen for: The top voice holds through the ii and V, then falls a whole step to the ninth. On the maj7 it stays where it is, as the third.
A minor-key tune can cadence on C#maj9 instead of the i, a softer landing a step below Eb. The ♭VII’s root doesn’t move: it becomes the ninth.
Listen for: The root of the ♭VII holds as the ninth while the other voices step. On the maj7 it has to fall a whole step to the root.
Heard in“Eight Miles High”“You Showed Me”
In which keys. Every note of C#maj9 belongs to C# major, F minor, Ab major and Bb minor.
Every note of C#maj9 is in C# major and C# lydian.
Each of those is a page: the scale across the neck, and the chords it harmonises into — which is where C#maj9 sits in it. Every scale.
Change one note of C#maj9 and you have (drop the ninth), (add the eleventh), (add the thirteenth), (the major third becomes the minor third), (drop the major seventh) or (the major seventh becomes the sixth).
C#maj9 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.