I just listened to a podcast by Open Source. In this podcast, they discuss the historical and current practice around copyright infringement, and claim that the tighter practice and debate of copyright has only developed in the last 20 years or so. It is an interesting discussion that you can find, along with the podcast, here.
They also brought forth a new distinction for me: plagarism versus copyright infringement. I had never differentiated between the two, but they claim that plagarism is an ethical wrong, determined by a community of artists (whether academic scholars, musicians, etc.) while copyright infringement is a legal one. There is a small intersection between the two. The example they give is if a journalist is pushed for time and stupidly grabs a column written by someone else in a copyrighted journal, puts his/her name at the top, and prints it.
There are some interesting discussions at Open Source’s site. I especially liked silvio.rabioso’s suggestions of further reading. More avenues to explore.