Degree iii — m7 (Mediant)

Between tonic and dominant

Prove it — just do the practice exercise.
Em7 Shell Voicing
E (R)G (♭3)D (♭7)
The iii degree sits between tonic and dominant:

• In C major: Em7
• Function: Weak tonic substitute
• Often starts extended turnarounds: iii – vi – ii – V

Roman numeral: iii (lowercase = minor)

The iii is rarely used as a standalone chord, but is important in sequences.