B♭ Altered — 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 · i°7Bbm7b5
Degree 2 · ii(maj7)CbmMaj7
Degree 3 · iii7Dbm7
Degree 4 · IV+maj7Ebbmaj7#5
Degree 5 · V7Fb7
Degree 6 · VI7Gb7
Degree 7 · vii°7Abm7b5