To a composer, the Bach two-part inventions are models of, well, invention. Here is an example:
Now that's how to write two independent voices with imitation. There is also a lot of invertible counterpoint. That's when you write passages where you can flip the two voices so the upper becomes the lower. It isn't quite as easy as it sounds. These were written for teaching purposes by Bach and are still used today. Even people who could care less about Bach-style counterpoint make use of the basic idea.
I think you can hear the way the vocal melody rises and then falls in waves, while the independent bass line descends. Paul came up with a lot of great bass lines. The reason I mention this is that I've noticed a trend towards obscurity. It may have begun with the third movement of this piece, which starts at around 7:04:
This is the third of Schoenberg's Five Pieces for Orchestra, op 16 entitled "Farben" (colors). It uses a newly-devised technique called "klangfarbenmelodie" or "sound-color-melody". The basic idea is to replace clear melodic counterpoint with changing instrumental colors. This and the other pieces in op 16 are very interesting in their own way. But. In the hands of more ordinary composers it becomes mush. There was a reason Bach taught his students counterpoint. And that Beethoven studied Bach's counterpoint. And that Chopin never went anywhere without a copy of the Well-Tempered Clavier. Finally we end up with something like this:
That really sounds like it is about to do something, or mean something, but it never does. This is called 'ambient' music and it originates with Brian Eno. It may have a function, but... Here is something similar by the Icelandic "post-rock" group Sigur Ros:
The problem I have with this is that there is no clarity: everything becomes a wash of sound with occasional fragments floating out. You can't really hear what's going on and you probably aren't supposed to. You are just supposed to float in the ocean of sound, lapping back and forth. Personally, I hate it! Obscurity is not a virtue in my book. Unless! Unless it is for a reason. I guess that makes it an 'instrumental' virtue. Something that may be of use to some other end. In itself obscurity is just ... bad. Here is something that uses ambiguity for good effect:
Now that music is going somewhere!