Last night I finished the 60 exercises that make up Part I of the Fux book. Musical lessons learned:
1. Occasional skips greater than a third help change the character of a line from an accompaniment to a melody. This is counterintuitive to me-- my instinct is to use steps whenever possible.
2. Parallel motion really does serve to undermine the momentum of the counterpoint and the interest of the harmony. Fux isn't kidding when he says that in florid counterpoint, parallel motion should be generally avoided.
3. However, I find parallel motion can be a nice effect near the end. It's a kind of pre-resolution calming. Like the piece has found its stride before it resolves.
4. Skips in the cantus firmus-- especially skips of more than a third-- introduce the possibility of collapsing the distinction with the counterpoint. This problem is acute when the skip narrows the distance between the two lines. One way to deal with this in florid counterpoint is to "cover" the skip with quarter notes. A run of quarter notes keeps the ear focused on the counterpoint, and helps keep it distinct from the cantus firmus.
5. In florid counterpoint, Fux allows eighth notes on the second and fourth beats. I tried using them in a bunch of exercises and always hated the way they sounded. I didn't end up keeping any eights.
6. I don't yet know if it's the nature of the modes, or the particulars of the cantus firmi Fux supplies for them, but there's no doubt that some modes are easier to write and pleasanter sounding than others. I've found that Dorian, Phrygian, and Ionian modes usually come together pretty easily. Lydian and Mixolydian are tough slogs that often sound bland. Aeloian is sometimes hard to get right, but I usually like sound of the result.
7. A lesson I learned from Wire's "Pink Flag" that is recapitulated by counterpoint exercises: with music, familiarity fosters enjoyment. If I spend two hours getting an exercise into a form I like a lot, then let it sit for a few days, I might dislike it when I listen to it with fresh ears. But if I listen to it four or five times in a row, I start to like it again. This helps explain why so much old classical music is formulaic, and so much popular music is repetitious. When you aren't dealing with a 30-second snippet that can be heard six times in short order, you've got to find some other way to secure the familiarity that fosters enjoyment.