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What Is Copyleft?

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Table of Contents

   * What Is Copyleft?

   * Translations of the GPL

   * Other Texts to Read

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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.

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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

programs.

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.

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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

     Internet

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FSF & GNU inquiries & questions to gnu@prep.ai.mit.edu. 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

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