• C D E F G Ab A B C.
• The Ab makes it a dimnished sixth.
• It makes the melodic parts line up on the strong parts of the beat:

C D : C→C: UnisonE F : C→E: M3G Ab : C→G: P5A B : C→A: M6C

• This gives us a nice chord if we play with the on-beat notes.
• In general, since we have 8 notes, if we start on the 1st, we will end on the 1st.
• This will be true if we put a half step anywhere .

§ Contrary motion

• Let's now look at how this behaves with contrary motion

C   C : "octave"D   B : M6E   A : P4F   Ab : m3G   G  : "unison"------ line of symmetryAb  F : M6A   E : P5B   D : m3C   C : "octave"