Typically, chords are built from scales using stacked 3rd intervals (every other note). You make ‘7th’ chords from four ‘3rds’ in sequence (1-3-5-7). Add another 3rd interval to this sequence (1-3-5-7-9) and you produce 9th chords. So in the key of C major it goes like this: Cmaj9 is: C (root), E (3rd), G (5th), B (maj 7 b ), D (9th). G9 is: G (root), B (3rd b ), D (5th), F ( 7), A (9th). Dm9 is: D (root), F ( 3), A (5th), C ( b 7), E (9th). You can also simply 'add' the 9th interval to a major triad to produce 'C add 9' or C (9). C add 9 is C (root), E (3rd), G (5th), D (9th). These chords are commonly found in…
