9th Chords on Guitar: Dominant 9, Major 9, Minor 9
Ninth chords are seventh chords with one more note stacked on top - the 9th, which is just the 2nd note of the scale an octave up. More notes, more flavor.
Dominant 9 (written as plain "9": C9, E9)
Formula: 1 - 3 - 5 - ♭7 - 9. Funk, blues, and R&B live on this chord. The word "9" alone always means the dominant (♭7) version.
C9
E9
The E9 shape is a barre-chord machine: slide it up so your index barres the 5th fret and add your pinky on the 7th fret of the thinnest string - that is A9. Same shape anywhere on the neck, named by the note under your barre on the thickest string.
Major 9 (maj9)
Formula: 1 - 3 - 5 - 7 - 9. Take the dreamy maj7 sound and add even more air. It shows up in jazz, soul, and lo-fi beats. On guitar, players often leave out the 5th to keep the chord playable - the ear fills it in.
Minor 9 (m9)
Formula: 1 - ♭3 - 5 - ♭7 - 9. Dark but rich. Em9 needs only two fingers and sounds like a film soundtrack.
Em9