B♭ Major — 7th chords
Four-note stacks of thirds on each degree — root, 3rd, 5th, 7th. The added 7th gives jazz, gospel, and modern classical voicings their distinctive colour.
All 7 seventh chords in sequence
Degree 1 · Imaj7Bbmaj7
Degree 2 · ii7Cm7
Degree 3 · iii7Dm7
Degree 4 · IVmaj7Ebmaj7
Degree 5 · V7F7
Degree 6 · vi7Gm7
Degree 7 · vii°7Am7b5