Copyright in copyleft licence?

Question

Is the copyright mentioned in GPL v3 used just for the sake of defining the word? (It's not copyrighted, but the word encompasses the same actions that would violate the copyright if it was copyrighted.)

To “propagate” a work means to do anything with it that, without permission, would make you directly or secondarily liable for infringement under applicable copyright law, except executing it on a computer or modifying a private copy. Propagation includes copying, distribution (with or without modification), making available to the public, and in some countries other activities as well.

Answer 1

No. GPL works are copyrighted (as are most creative works basically everywhere in the world, as soon as they're created, whether or not the author does anything about it), and copyright is what gives the GPL "teeth".

Without copyright, you would generally be able to duplicate and distribute programs without any kind of license or permission from the author. Copyright law restricts your ability to do those things. The GPL is a license, which means it's a grant of permission. It says that you may copy and modify and do other things, provided that you comply with the other provisions set out in the license.

Quoting from the GPL v3:

You are not required to accept this License in order to receive or run a copy of the Program. [...] However, nothing other than this License grants you permission to propagate or modify any covered work. These actions infringe copyright if you do not accept this License.

So if you were to distribute some GPL-licensed software in a way that didn't comply with the terms of the license, the legal framework that would allow someone to sue you to stop you doing that would be copyright law.

Answer 2

GPL does not purport that there is no copyright in a work to which the license applies: the works are still in copyright. It relies on the notion of copyright (which it redefines to include "similar things") on order to identify what rights are granted (you have the right to do things that would be copyright infringement, if you did those acts without permission, but I give you permission). It has to rely on copyright restrictions in order to impose restrictions on distribution in §4-6 – if you violate the conditions of those sections, you do not have permission to copy, and you will have infringed copyright. By explicitly mentioning copyright, they have reminded the user that this is not a work in the public domain and that it is still protected by law.