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What Is Copyleft?
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Table of Contents
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   * What Is Copyleft?
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   * Translations of the GPL
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   * Other Texts to Read
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What Is Copyleft?
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The simplest way to make a program free is to put it in the public domain
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(18k characters), uncopyrighted. This allows people to share the program
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and their improvements, if they are so minded. But it also allows
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uncooperative people to convert the program into proprietary software (18k
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characters). They can make changes, many or few, and distribute the result
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as a proprietary product. People who receive the program in that modified
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form do not have the freedom that the original author gave them; the
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middleman has stripped it away.
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In the GNU project, our aim is to give all users the freedom to
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redistribute and change GNU software. If middlemen could strip off the
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freedom, we might have many users, but those users would not have freedom.
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So instead of putting GNU software in the public domain, we ``copyleft''
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it. Copyleft says that anyone who redistributes the software, with or
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without changes, must pass along the freedom to further copy and change it.
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Copyleft guarantees that every user has freedom.
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Copyleft provides another benefit as well. People who write improvements in
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free software often work for companies or universities that would do almost
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anything to get money. A programmer may want to contribute her changes to
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the community, but her employer may ``see green'' and insist on turning the
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changes into a commercial product.
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When we explain to the employer that it is illegal to distribute the
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improved version except as free software, the employer usually decides to
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release it as free software rather than throw it away.
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To copyleft a program, first we copyright it; then we add distribution
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terms, which are a legal instrument that gives everyone the rights to use,
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modify, and redistribute the program's code or any program derived from it
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but only if the distribution terms are unchanged. Thus, the code and the
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freedoms become legally inseparable.
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Proprietary software developers use copyright to take away the users'
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freedom; we use copyright to guarantee their freedom. That's why we reverse
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the name, changing ``copyright'' into ``copyleft.''
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Copyleft is a general concept; there are many ways to fill in the details.
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In the GNU Project, the specific distribution terms that we use are
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contained in the GNU General Public License (20k characters) (GNU GPL). An
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alternate form, the GNU Library General Public License (27k characters)
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(GNU LGPL), applies to a few (but not all) GNU libraries. The library
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license permits linking the libraries into proprietary executables under
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certain conditions.
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The appropriate license is included in many manuals and in each GNU source
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code distribution (usually in files named COPYING (20k characters) and
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COPYING.LIB (27k characters)).
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The GNU GPL is designed so that you can easily apply it to your own program
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if you are the copyright holder. You don't have to modify the GNU GPL to do
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this, just add notices to your program which refer properly to the GNU GPL.
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If you would like to copyleft your program with the GNU GPL, please see the
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instructions at the end (20k characters) of the GPL text. If you would like
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to copyleft your library with the GNU LGPL, please see the instructions at
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the end (27k characters) of the LGPL text (note you can also use the
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ordinary GPL for libraries).
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Using the same distribution terms for many different programs makes it easy
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to copy code between various different programs. Since they all have the
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same distribution terms, there is no need to think about whether the terms
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are compatible. The Library GPL includes a provision that lets you alter
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the distribution terms to the ordinary GPL, so that you can copy code into
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another program covered by the GPL.
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Translations of the GPL
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Here are some translations of the GNU GPL done by others.
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   * A Japanese translation of the GPL.
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   * A German translation of the GPL.
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These versions are not official. Legally speaking, the original (English)
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version of the GPL is what specifies the actual distribution terms for GNU
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programs.
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The reason the FSF does not approve these translations as officially valid
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is that checking them would be difficult and expensive (needing the help of
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bilingual lawyers in other countries). Even worse, if an error did slip
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through, the results could be disastrous for the whole free software
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community. As long as the translations are unofficial, they can't do any
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harm, and we hope they help more people understand the GPL.
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Other Texts to Read
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This first group of articles directly address the philosophy of the GNU
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project and free software:
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   * What is Free Software?
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   * Why Software Should Not Have Owners
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   * Selling Free Software Can Be Ok!
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   * Categories of Free Software (18k characters)
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   * Free software is more reliable!
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   * What is the Free Software Foundation?
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   * What is Copyleft?
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   * Confusing Words which You Might Want to Avoid
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   * History of the GNU Project
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   * The GNU Manifesto (31k characters)
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   * Why there are no GIF files on GNU web pages
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This second group of articles deal with related topics but are not directly
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about the GNU project:
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   * How to Protect the Right to Write Software (independent of whether
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     it's free or not)
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   * Where the Copyright System and Government Plans are Leading Us
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   * The Right Way to Tax DAT (22k characters)
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   * Studies Find Reward Often No Motivator
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   * A speech that Richard Stallman gave in 1986 at the Royal Institute of
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     Technology in Sweden
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   * How to Protect the Freedoms of Speech, Press, and Association on the
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     Internet
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FSF & GNU inquiries & questions to gnu@prep.ai.mit.edu. Other ways to
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contact the FSF.
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Copyright (C) 1996, 1997 Free Software Foundation, Inc., 59 Temple Place -
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Suite 330, Boston, MA 02111, USA
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Verbatim copying and distribution is permitted in any medium, provided this
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notice is preserved.
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Updated: 4 Aug 1997 tower
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