Second degree of the diminished seventh · Rules
In a diminished seventh going to I, the second degree rises to the third. It may fall to the tonic if it lies above the lowered sixth degree; if it lies below, it is flagged as less usual.
- Second degree of the diminished seventh: In a diminished seventh going to I, the second degree rises to the third. It may fall to the tonic if it lies above the lowered sixth degree; if it lies below, it is flagged as less usual. (Piston, ch. 21, p. 320)