Andy Oram published a very interesting document that describes the history of copyright laws. It explains how it drifted with time and what are the internal concepts of copyright. For instance, he highlights the difference between patent and copyright. Patent protects a function whereas copyright protects an expression. You have to fight to get the protection of patent whereas you have to fight to leave the protection of copyright (that is “on” by default)
The document is really interesting to read if you are interested to understand what copyright is, and how it arrived where it is. The only critic is that (as for many paper on this subject) is mainly US centric.

The address of the paper is How copyright got to its current state

Thank you Jean Jacques for the pointer. :Wink: