Free Software, Free Society: selected essays of Richard M. Stallman. 2nd edition.

Chapter 21. What Is Copyleft?

Copyleft is a general method for making a program (or other work) free, and requiring all modified and extended versions of the program to be free as well.

The simplest way to make a program free software is to put it in the public domain, uncopyrighted. This allows people to share the program and their improvements, if they are so minded. But it also allows uncooperative people to convert the program into proprietary software. They can make changes, many or few, and distribute the result as a proprietary product. People who receive the program in that modified form do not have the freedom that the original author gave them; the middleman has stripped it away.

In the GNU Project, our aim is to give all users the freedom to redistribute and change GNU software. If middlemen could strip off the freedom, we might have many users, but those users would not have freedom. So instead of putting GNU software in the public domain, we “copyleft” it. Copyleft says that anyone who redistributes the software, with or without changes, must pass along the freedom to further copy and change it. Copyleft guarantees that every user has freedom.

Copyleft also provides an incentive for other programmers to add to free software. Important free programs such as the GNU C++ compiler exist only because of this.

Copyleft also helps programmers who want to contribute improvements to free software get permission to do so. These programmers often work for companies or universities that would do almost anything to get more money. A programmer may want to contribute her changes to the community, but her employer may want to turn the changes into a proprietary software product.

When we explain to the employer that it is illegal to distribute the improved version except as free software, the employer usually decides to release it as free software rather than throw it away.

To copyleft a program, we first state that it is copyrighted; then we add distribution terms, which are a legal instrument that gives everyone the rights to use, modify, and redistribute the program’s code, or any program derived from it, but only if the distribution terms are unchanged. Thus, the code and the freedoms become legally inseparable.

Proprietary software developers use copyright to take away the users’ freedom; we use copyright to guarantee their freedom. That’s why we reverse the name, changing “copyright” into “copyleft.”

Copyleft is a way of using of the copyright on the program. It doesn’t mean abandoning the copyright; in fact, doing so would make copyleft impossible. The “left” in “copyleft” is not a reference to the verb “to leave”—only to the direction which is the inverse of “right.”

Copyleft is a general concept, and you can’t use a general concept directly; you can only use a specific implementation of the concept. In the GNU Project, the specific distribution terms that we use for most software are contained in the GNU General Public License. The GNU General Public License is often called the GNU GPL for short. There is also a Frequently Asked Questions page about the GNU GPL, at http://gnu.org/licenses/gpl-faq.html. You can also read about why the FSF gets copyright assignments from contributors, at http://gnu.org/copyleft/why-assign.html.

An alternate form of copyleft, the GNU Lesser General Public License (LGPL), applies to a few (but not all) GNU libraries. To learn more about properly using the LGPL, please read the article “Why You Shouldn’t Use the Lesser GPL for Your Next Library,” available at http://gnu.org/philosophy/why-not-lgpl.html.

The GNU Free Documentation License (FDL) is a form of copyleft intended for use on a manual, textbook or other document to assure everyone the effective freedom to copy and redistribute it, with or without modifications, either commercially or noncommercially.

The appropriate license is included in many manuals and in each GNU source code distribution.

All these licenses are designed so that you can easily apply them to your own works, assuming you are the copyright holder. You don’t have to modify the license to do this, just include a copy of the license in the work, and add notices in the source files that refer properly to the license.

Using the same distribution terms for many different programs makes it easy to copy code between various different programs. When they all have the same distribution terms, there is no problem. The Lesser GPL, version 2, includes a provision that lets you alter the distribution terms to the ordinary GPL, so that you can copy code into another program covered by the GPL. Version 3 of the Lesser GPL is built as an exception added to GPL version 3, making the compatibility automatic.

If you would like to copyleft your program with the GNU GPL or the GNU LGPL, please see the license instructions page, at http://gnu.org/copyleft/gpl- howto.html, for advice. Please note that you must use the entire text of the license you choose. Each is an integral whole, and partial copies are not permitted.

If you would like to copyleft your manual with the GNU FDL, please see the instructions at the end of the FDL text, and the GFDL instructions page, at http://gnu.org/copyleft/fdl-howto.html. Again, partial copies are not permitted.

Copyright © 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.

This essay was first published on http://gnu.org, in 1996. This version is part of Free Software, Free Society: Selected Essays of Richard M. Stallman, 2nd ed. (Boston: GNU Press, 2010).

Verbatim copying and distribution of this entire chapter are permitted worldwide, without royalty, in any medium, provided this notice is preserved.

Chapter 22. Copyleft: Pragmatic Idealism

Every decision a person makes stems from the person’s values and goals. People can have many different goals and values; fame, profit, love, survival, fun, and freedom, are just some of the goals that a good person might have. When the goal is a matter of principle, we call that idealism.

My work on free software is motivated by an idealistic goal: spreading freedom and cooperation. I want to encourage free software to spread, replacing proprietary software that forbids cooperation, and thus make our society better.

That’s the basic reason why the GNU General Public License is written the way it is—as a copyleft. All code added to a GPL-covered program must be free software, even if it is put in a separate file. I make my code available for use in free software, and not for use in proprietary software, in order to encourage other people who write software to make it free as well. I figure that since proprietary software developers use copyright to stop us from sharing, we cooperators can use copyright to give other cooperators an advantage of their own: they can use our code.

Not everyone who uses the GNU GPL has this goal. Many years ago, a friend of mine was asked to rerelease a copylefted program under noncopyleft terms, and he responded more or less like this: “Sometimes I work on free software, and sometimes I work on proprietary software—but when I work on proprietary software, I expect to get paid.”