The guitar chords on this page are built from the C major scale. The C major scale has 7 scale steps. They are the notes C,D,E,F,G,A,B.
The Cmaj9 Chord
A dominant ninth is a dominant chord with a ninth (the ninth would be the same note as the 2nd: D). A ninth chord, as an extended chord, typically includes the seventh along with the basic triad structure. Thus, a Cmaj9 consists of C E G B and D.
The C9 Chord
When the symbol “9” is not preceded by the word “major” or “maj”, the implied seventh is a minor seventh.
C9 consists of C E G B and D and would usually be expected to resolve into the F major chord.
F is the implied key because of usual role of the dominant. C is the dominant of F.
The Cm9 Chord
The minor ninth chord is played with the third and seventh both flattened. The formula is 1, 3, 5, 7, 9. This chord is written as Cm9. This chord has a more “bluesy” sound and fits very well with the dominant 9th.
The C Added Ninth Chord
An added ninth chord is a major triad with an added ninth. Cadd9 consists of C E G and D. The 9th scale step is actually the same note as the 2nd scale step. In this case the 2nd/9th is D. Added ninth chords are different from other ninth chords because the seventh is not included.