Z:gnu-www-ja-enforcing-gpl--3b3c98-The GPL, on the other hand, su/en

The GPL, on the other hand, subtracts from copyright rather than adding to it. The license doesn't have to be complicated, because we try to control users as little as possible. Copyright grants publishers power to forbid users to exercise rights to copy, modify, and distribute that we believe all users should have; the GPL thus relaxes almost all the restrictions of the copyright system. The only thing we absolutely require is that anyone distributing GPL'd works or works made from GPL'd works distribute in turn under GPL. That condition is a very minor restriction, from the copyright point of view. Much more restrictive licenses are routinely held enforceable: every license involved in every single copyright lawsuit is more restrictive than the GPL.