Key
Chords in G Lydian
G Lydian is built from the notes G, A, B, C#, D, E and F#. Its scale carries 2 sharps. Harmonising that scale in thirds gives seven chords — 3 majors, 3 minors and 1 diminished — starting on G as the I. The chord on the fifth degree is D, a major V, so G Lydian has the leading tone that makes a D-to-G cadence sound final.
Beyond those seven, G Lydian commonly borrows Gm (i), Adim (iiø), Bb (bIII), Cm (iv) and Dm (v) from the parallel minor — the mixture chords that give a progression somewhere unexpected to go.
The seven chords
Extended to four notes each, the same seven degrees give Gmaj7, A7, Bm7, C#m7b5, Dmaj7, Em7, F#m7.
Borrowed chords
Capo 7 and play C Lydian shapes to sound G Lydian.
All eight capo positions for G Lydian →