mapping SCALE DEGREES

​The I scale degree is where music starts and ends. It is called the tonic. 

​The vi scale degree can also serve as the tonic as well as the iii.

​Movement from the I and vi scale degrees is always to the V scale degree. The V is called the dominate. It creates harmonic instability and leads back to the tonic.
​When I moves to vi and back to I it is normally through a I6. 

​But like the tonic, the V scale degree also has another chord that can function as a dominate.  It is the diminished vii.
So I and vi can go directly to viidim and V or move towards the viidim and V through the pre-dominant .

​The IV scale degree is called  pre-dominate meaning it leads to the dominate.
The ii scale degree is also pre-dominate. 
The ii in first inversion (ii6) is actually more common than the IV.

So the primary harmonic functions are: ​

• Tonic Function (I, vi, iii), 
• Dominant Function (V, viidim)  
• Pre-Dominant Function (ii, IV)​

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