75.5Level 2 — allow one fourth per phrase

Now each phrase must contain at least one:

perfect fourth

or augmented/diminished fourth if appropriate.

Example:

C→F

D→G

E♭→A♭? A♭ is not in C Dorian, so use context carefully.

Inside C Dorian, examples include:

C→F

D→G

E♭→A

F→B♭

G→C.

Immediately the line opens up.