The definition of what is a derivative work is IMHO overreaching in GPL based licenses.
GPL doesn’t use the word “derive” and specifies modified work in a way that is consistent with the customary legal definition.
People twist things around because they want to use GPLed code without “paying” for it, but really at the end of the day it’s just an ordinary license agreement but instead of paying cash to use it you agree to give users the freedom to modify and/or redistribute the code.
Just like any other licensed code you can agree to the terms and use the code or disagree with the terms and use something else.
> People twist things around because they want to use GPLed code without “paying” for it, but really at the end of the day it’s just an ordinary license agreement but instead of paying cash to use it you agree to give users the freedom to modify and/or redistribute the code.
You mean, instead of paying cash to use it, you pay with your property (your code). An old school barter exchange.
Source of confusion probably comes from overuse of the word "free" by people promoting GPL, which is like you said, just an ordinary license agreement.
It's not that simple. If it was just about "my" code, this would indeed your claimed barter exchange. But often, say in industry, the code that you develop is combined with a lot of third party code and libraries for which you simply do not have the permission to put them under GPL.
In fact, I suspect that a legal definition of exactly what constitutes a derived work of a program may be more broad than the GPL's definition. For example, it's plausible to me that a program which calls `sh` as a fundamental part of its functioning could be found to represent a derivative work of `sh` per copyright laws.
What term defines the scope to which copyleft applies to?
So, only copyright law itself can say whether, for example, this comment I'm making is a derived work of your own comment, or if it is an original work of my own. If it is a derived work of your comment, then you are the copyright holder for this comment I'm making and you can choose to write a license that allows me to distribute it or nor or whatever else. If it is not a derived work, then I am the copyright holder, and I don't require any license from you to distribute this comment.
So, if copyright law were to say "a computer program A is a derived work of program B if and only if it is produced from the same source code of A or textual modifications of the code of A" (very implausible, but just for the sake of argument), then there would be no difference between the GPL and the LGPL, and you could freely link to a GPL program and distribute the result under a proprietary license (you'd still have to distribute the source code of the original GPL program, of course).
