Add 9 adds the 9th to a major triad without the 7th (1–3–5–9). It brightens a plain major with a shimmering colour, common in pop and acoustic playing.
NotesE · F♯ · G♯ · B
Formula1 · 9 · 3 · 5
Every add 9 chord tone across the neck. Solo with these and you spell the chord — that's the difference between running a scale and playing the changes.
