Chords in Ab Lydian

Ab Lydian is built from the notes Ab, Bb, C, D, Eb, F and G. Its scale carries 3 flats. Harmonising that scale in thirds gives seven chords — 3 majors, 3 minors and 1 diminished — starting on Ab as the I. The chord on the fifth degree is Eb, a major V, so Ab Lydian has the leading tone that makes a Eb-to-Ab cadence sound final.

Beyond those seven, Ab Lydian commonly borrows Abm (i), Bbdim (iiø), Cb (bIII), Dbm (iv) and Ebm (v) from the parallel minor — the mixture chords that give a progression somewhere unexpected to go.