The Rule of the Octave - Insanguine's Partimento Rules Book P. 1

THE RULE OF THE OCTAVE

Firstly, one should know that each key has seven degrees, which are 1, 2, 3, 4, 5, 6, and 7.

1 takes a 3rd, 5th, and 8ve.

2 takes a minor 3rd and a major 6th. It can also have a 4th.

3 takes a 3rd and a 6th.

4 takes a 3rd, 5th, and 6th. When it descends from 5 and goes to 3, it takes a 2nd and augmented 4th.

5 takes a 3rd, 5th, and 8ve.

6 takes a 3rd and 6th, and when it descends it takes a major 6th, optionally having a 3rd and 4th.

7, when it ascends to the tonic, takes a 3rd, diminished 5th, and 6th; and when it descends, it then takes a 3rd and 6th.