Counterpoint is simply a re-contextualizing of material. It's not the same as permutation of material--although that is often crucial to counterpoint--it's taking the material from one situation and putting it into another. Bach placed fugue themes in different voices and different keys and even on different scale degrees within keys so that they would have different tonal functions.
Throughout my musical life I've been fascinated by counterpoint. I took lessons in 16th century and 18th century counterpoint from a mentor as an undergrad. I never felt like I really got it, but it is a pretty dated set of rules (I mean I don't feel like I've internalized the way contemporary composers would have). Since then I've come to realize that it's not the rules of any specific model of counterpoint, but it's the abstract notion of music set against music in some kind of conceptual space. I figured that out in David Sargent's seminar on 20th century counterpoint where we studied, among others, dynamics counterpoint in Ruth Crawford Seeger's string quartet and textural counterpoint in Penderecki's Threnody.
I recently heard a lecture by the composer William Kleinsasser who took the abstraction a bit farther. He talked about pieces being in counterpoint with the memory of other pieces. For him it was kind of a mode of influence. In other words, when he composes he sees the current project as having a contrapuntal relationship with earlier pieces that he has written.
When I heard Kleinsasser's lecture I felt like he hit on something I had been thinking alot about lately--counterpoint between pieces (or between formal sections--formal counterpoint). Except in my concept, the pieces are literally existing and being heard simultaneously. In a sense it's like hearing a fugue answer and countersubject played simultaneously. Both are fully formed, legitimate melodies, but it's in the counterpoint between them that the real musical interest lies. If the melodies move to other places (keys, registers, tonal function, etc.), that is if the composer re-contextualizes the melodies, then the space between also changes. In other words counterpoint focuses on the space between and through various contrapuntal techniques, the composer can manipulate that space.
A couple of tangential ideas:
By placing the "real musical interest" in the space between the two melodies, it also point to a breakdown in the subject-object binary, something I'm also very interested in.
I will need to look at Lachenmann again now. He has been my primary example of re-contextualizing, though I haven't considered his music in terms of counterpoint. If counterpoint is simply a re-contextualizing of music, then his music is likely in counterpoint with something, albeit possibly an unheard something--memory? tradition?