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What Is Copyleft?


Table of Contents

   * What Is Copyleft?
   * Translations of the GPL
   * Other Texts to Read


What Is Copyleft?

The simplest way to make a program free is to put it in the public domain
(18k characters), 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 (18k
characters). 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 provides another benefit as well. People who write improvements in
free software often work for companies or universities that would do almost
anything to get money. A programmer may want to contribute her changes to
the community, but her employer may ``see green'' and insist on turning the
changes into a commercial 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, first we copyright it; 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 general concept; there are many ways to fill in the details.
In the GNU Project, the specific distribution terms that we use are
contained in the GNU General Public License (20k characters) (GNU GPL). An
alternate form, the GNU Library General Public License (27k characters)
(GNU LGPL), applies to a few (but not all) GNU libraries. The library
license permits linking the libraries into proprietary executables under
certain conditions.

The appropriate license is included in many manuals and in each GNU source
code distribution (usually in files named COPYING (20k characters) and
COPYING.LIB (27k characters)).

The GNU GPL is designed so that you can easily apply it to your own program
if you are the copyright holder. You don't have to modify the GNU GPL to do
this, just add notices to your program which refer properly to the GNU GPL.

If you would like to copyleft your program with the GNU GPL, please see the
instructions at the end (20k characters) of the GPL text. If you would like
to copyleft your library with the GNU LGPL, please see the instructions at
the end (27k characters) of the LGPL text (note you can also use the
ordinary GPL for libraries).

Using the same distribution terms for many different programs makes it easy
to copy code between various different programs. Since they all have the
same distribution terms, there is no need to think about whether the terms
are compatible. The Library GPL 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.

Translations of the GPL

Here are some translations of the GNU GPL done by others.

   * A Japanese translation of the GPL.
   * A German translation of the GPL.

These versions are not official. Legally speaking, the original (English)
version of the GPL is what specifies the actual distribution terms for GNU

The reason the FSF does not approve these translations as officially valid
is that checking them would be difficult and expensive (needing the help of
bilingual lawyers in other countries). Even worse, if an error did slip
through, the results could be disastrous for the whole free software
community. As long as the translations are unofficial, they can't do any
harm, and we hope they help more people understand the GPL.

Other Texts to Read

This first group of articles directly address the philosophy of the GNU
project and free software:

   * What is Free Software?
   * Why Software Should Not Have Owners
   * Selling Free Software Can Be Ok!
   * Categories of Free Software (18k characters)
   * Free software is more reliable!
   * What is the Free Software Foundation?
   * What is Copyleft?
   * Confusing Words which You Might Want to Avoid
   * History of the GNU Project
   * The GNU Manifesto (31k characters)
   * Why there are no GIF files on GNU web pages

This second group of articles deal with related topics but are not directly
about the GNU project:

   * How to Protect the Right to Write Software (independent of whether
     it's free or not)
   * Where the Copyright System and Government Plans are Leading Us
   * The Right Way to Tax DAT (22k characters)
   * Studies Find Reward Often No Motivator
   * A speech that Richard Stallman gave in 1986 at the Royal Institute of
     Technology in Sweden
   * How to Protect the Freedoms of Speech, Press, and Association on the


FSF & GNU inquiries & questions to Other ways to
contact the FSF.

Copyright (C) 1996, 1997 Free Software Foundation, Inc., 59 Temple Place -
Suite 330, Boston, MA 02111, USA

Verbatim copying and distribution is permitted in any medium, provided this
notice is preserved.

Updated: 4 Aug 1997 tower