Degree ii — m7 (Subdominant Sub)

The most important minor chord in jazz

Prove it — just do the practice exercise.
Dm7 Shell Voicing
D (R)F (♭3)C (♭7)
The ii degree is the star of jazz:

• In C major: Dm7
• Function: Subdominant (substitute for IV)
• Leads to the dominant: ii → V → I

Roman numeral: ii (lowercase = minor)

The ii-V-I is THE most important progression in jazz. The ii replaces the IV almost everywhere.