A little background: I am teaching myself species counterpoint by reading multiple texts and doing exercises. My primary text is Salzer and Schacter’s “Counterpoint in Composition,” which I really like. I’ve also found of lot of great online resources like “Open Music Theory” and “Sound Patterns.” I’ve been checking my counterpoint exercises using Are Nova’s excellent “Counterpointer” program, which identifies potential errors such as parallel 5ths.
My question: In designing a counterpoint melody, all texts allow ascending and descending leaps of 3rds, 4ths, 5ths and Octaves. Things get a little fuzzier with 6ths. All sources prohibit ascending and descending major 6ths.
My confusion is about leaps of a minor 6th.
Most sources (when they discuss this at all), allow for ascending leaps of minor 6ths but not descending leaps of a minor 6th. Salzer shows descending leaps of a minor 6th in some of his examples but never discusses the issue.
Should I avoid descending leaps of a minor 6th? Why?