D Ionian — 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 · Imaj7Dmaj7
Degree 2 · ii7Em7
Degree 3 · iii7F#m7
Degree 4 · IVmaj7Gmaj7
Degree 5 · V7A7
Degree 6 · vi7Bm7
Degree 7 · vii°7C#m7b5