For the "normal" cases, you're right: you can have copyright on the original parts of a derived work. You are fully right though that the original work's author does not in any circumstance get the copyright for the derived work. That was a confusion on my part.

> But even if I were to violate the terms of the GPL (thus terminating my rights under the GPL), I still would not lose my copyright interest in the program I wrote, only my right to distribute it.

As far as I understand though, this is not true. If you were not authorized to use the original work, then even the original parts of your work are in fact not protected by copyright at all. So, if, say, I take a Spiderman comic and add an extra page of fanart at the end, without any authorization from Marvel/Disney, then my extra page of fanart is not protected by copyright at all, and anyone is free to copy it (unless it also infringes on Marvel/Disney's copyright of course) [0]:

> Only the owner of copyright in a work has the right to prepare, or to authorize someone else to create, an adaptation of that work. The owner of a copyright is generally the author or someone who has obtained the exclusive rights from the author. In any case where a copyrighted work is used without the permission of the copyright owner, copyright protection will not extend to any part of the work in which such material has been used unlawfully. The unauthorized adaptation of a work may constitute copyright infringement.

[0] https://copyright.gov/circs/circ14.pdf

My understanding is that "a work" and "a product" are different things. If I sell you a bundle of three books, the bundle is a product, but each book is an individual work and caries its own copyright. Even a single book may contain 5 short stories, each with a different copyright holder and license.

Similarly, I can sell you one CD that contains three different works with different licenses. Now, it is true that the GPL license does seem to say that you can't distribute a modified GPL work on the same CD as a non-GPL work, which would not fall under copyright law, it would just be an arbitrary requirement of the license that you have to accept if you want to be able to distribute the GPL work at all (by default, you're not allowed to distribute copyrighted work at all - it's only the terms of the license that allow you to).

However, the derived work problem comes more into question when you write a program that only works if it is linked with, say, glibc. The question becomes: is your program a separate work from glibc, or is it a derived work of glibc? If it is a derived work, then the GNU project is the copyright holder of the program you wrote, and you're not allowed to distribute it at all unless you get some license from them. If it is NOT a derived work, then you are at least free to distribute your program however you want, and tell your customers "just download glibc from gnu.org, put it at this path, then start my program", and the glibc license could do nothing to stop you since it doesn't apply in any way.

An analogy with books would be you writing a book that's meant as a sequel to Harry Potter. It is quite well established that even if your book is fully original, if it uses characters from Harry Potter by name, or locations or other key concepts, then your book is a derived work of the Harry Potter franchise and you're not allowed to sell it even if you're not directly using any piece of the originals.

Either way though, if you're creating a derived work, the license of the original can allow you to distribute your derived work under any terms they want. A license could say "you can distribute derived works for free on Wednesdays, but you have to pay a royalty if it's any other day of the week". Or, more interestingly, the license could say "you can distribute derived works without any conditions if they only access our original work through DLOPEN, but if they are accessing it through static linking, you must release the code and build instructions for your derived work" - this is what the LGPL does.