Copyleft
Copyleft is the legal technique of granting certain freedoms over copies of copyrighted works with the requirement that the same rights be preserved in derivative works. In this sense, freedoms refers to the use of the work for any purpose, and the ability to modify, copy, share, and redistribute the work, with or without a fee. Licenses which implement copyleft can be used to maintain copyright conditions for works ranging from computer software, to documents, art, and scientific discoveries. Similar approaches have been applied to certain patents.
Copyleft software licenses are considered protective or reciprocal : they require that information necessary for reproducing and modifying the work be made available to recipients of the software program. This information is most commonly in the form of source code files, which usually contain a copy of the license terms and acknowledge the authors of the code. Copyleft helps ensure everyone's rights to freely use the product but it prohibits owning, registering copyright and earning royalties from copyright.
Notable copyleft licenses include the GNU General Public License, originally written by Richard Stallman, which was the first software copyleft license to see extensive use; the Mozilla Public License; the Free Art License; and the Creative Commons share-alike license condition—with the last two intended for non-software works, such as documents and pictures, both academic or artistic in nature. Wikipedia is copyleft under the Creative Commons Attribution-ShareAlike license.
History
's Palo Alto Tiny BASIC for the Intel 8080 appeared in Dr. Dobb's Journal in May 1976. The listing begins with the title, author's name, and date, but also has "@COPYLEFT ALL WRONGS RESERVED".The concept of copyleft was described in Richard Stallman's GNU Manifesto in 1985, where he wrote:
Stallman's motivation was that a few years earlier he had worked on a Lisp interpreter. Symbolics asked to use the Lisp interpreter, and Stallman agreed to supply them with a public domain version of his work. Symbolics extended and improved the Lisp interpreter, but when Stallman wanted access to the improvements that Symbolics had made to his interpreter, Symbolics refused. Stallman then, in 1984, proceeded to work towards eradicating this emerging behavior and culture of proprietary software, which he named software hoarding. This was not the first time Stallman had dealt with proprietary software, but he deemed this interaction a "turning point". He justified software sharing, protesting that when sharing, the software online can be copied without the loss of the original piece of work. The software can be used multiple times without ever being damaged or worn out.
As Stallman deemed it impractical in the short term to eliminate current copyright law and the wrongs he perceived it to perpetuate, he decided to work within the framework of existing law; in 1985, he created his own copyright license, the Emacs General Public License, the first copyleft license. This later evolved into the GNU General Public License, which is now one of the most popular free-software licenses. For the first time, a copyright holder had taken steps to ensure that the maximal number of rights be perpetually transferred to a program's users, no matter what subsequent revisions anyone made to the original program. This original GPL did not grant rights to the public at large, only those who had already received the program; but it was the best that could be done under existing law.
The new license was not at this time given the copyleft label. Richard Stallman stated that the use of "Copyleft" comes from Don Hopkins, who mailed him a letter in 1984 or 1985, on which was written: "Copyleft – all rights reversed", which is a pun on the common copyright disclaimer "all rights reserved".
In France, a series of meetings taking place in 2000 under the title "Copyleft Attitude" gave birth to the Free Art License, theoretically valid in any jurisdiction bound by the Berne Convention and recommended by Stallman's own Free Software Foundation. Shortly thereafter, a separate, unrelated initiative in the United States yielded the Creative Commons license, available since 2001 in both permissive and copyleft variants and more specifically tailored to US law.
Copyleft principles
Freedom
While copyright law gives software authors control over copying, distribution and modification of their works, the goal of copyleft is to give all users of the work the freedom to carry out all of these activities. The Free Software Definition lists "four essential freedoms" of software use:- The freedom to run the program as you wish, for any purpose.
- The freedom to study how the program works, and change it so it does your computing as you wish. Access to the source code is a precondition for this.
- The freedom to redistribute copies so you can help others.
- The freedom to distribute copies of your modified versions to others. By doing this you can give the whole community a chance to benefit from your changes. Access to the source code is a precondition for this.
Reciprocity
Instead of allowing a work to fall completely into the public domain, where no ownership of copyright is claimed, copyleft allows authors to impose restrictions on the use of their work. One of the main restrictions imposed by copyleft is that derived works must also be released under a compatible copyleft license.This is due to the underlying principle of copyleft: that anyone can benefit freely from the previous work of others, but that any modifications to that work should benefit everyone else as well, and thus must be released under similar terms. For this reason, copyleft licenses are also known as reciprocal licenses: any modifiers of a copyleft-licensed work are expected to reciprocate the author's action of copyleft-licensing the software by also copyleft-licensing any derivatives they might have made. Because of this requirement, copyleft licenses have also been described as "viral" due to their self-perpetuating terms.
In addition to restrictions on copying, copyleft licenses address other possible impediments. They ensure that rights cannot be later revoked, and require the work and its derivatives to be provided in a form that allows further modifications to be made. In software, this means requiring that the source code of the derived work be made available together with the software itself.
Economic incentive
The economic incentives to work on copyleft content can vary. Traditional copyright law is designed to promote progress by providing economic benefits to creators. When choosing to copyleft their work, content creators may seek complementary benefits like recognition from their peers.In the world of computer programming, copyleft-licensed computer programs are often created by programmers to fill a need they have noticed. Such programs are often published with a copyleft license simply to ensure that subsequent users can also freely use modified versions of that program. This is especially true for creators who wish to prevent "open source hijacking", or the act of reusing open-source code and then adding extra restrictions to it, an action prevented by copyleft-licensing the software. Some creators, such as Elastic, feel that preventing commercial enterprises from using and then selling their product under a proprietary license is also an incentive.
Furthermore, the open-source culture of programming has been described as a gift economy, where social power is determined by an individual's contributions. Contributing to or creating open-source, copyleft-licensed software of high quality can lead to contributors gaining valuable experience and can lead to future career opportunities.
Copyleft software has economic effects beyond individual creators. The presence of quality copyleft software can force proprietary software developers to increase the quality of their software to compete with free software. This may also have the effect of preventing monopolies in areas dominated by proprietary software. However, competition with proprietary software can also be a reason to forgo copyleft. The Free Software Foundation recommends that when "widespread use of the code is vital for advancing the cause of free software", allowing the code to be copied and used freely is more important than a copyleft.
Copyleft application
Common practice for using copyleft is to codify the copying terms for a work with a license. Any such license typically includes all the provisions and principles of copyleft inside the license's terms. This includes the freedom to use the work, study the work, copy, and share the work with others, modify the work, and distribute exact or modified versions of that work, with or without a fee.Unlike similar permissive licenses that also grant these freedoms, copyleft licenses also ensure that any modified versions of a work covered by a copyleft license must also grant these freedoms. Thus, copyleft licenses have conditions: that modifications of any work licensed under a copyleft license must be distributed under a compatible copyleft scheme and that the distributed modified work must include a means of modifying the work. Under fair use, however, copyleft licenses may be superseded, just like regular copyrights. Therefore, any person utilizing a source licensed under a copyleft license for works they invent is free to choose any other license provided they meet the fair use standard.
Copyleft licenses necessarily make creative use of relevant rules and laws to enforce their provisions. For example, when using copyright law, those who contribute to a work under copyleft usually must gain, defer, or assign copyright holder status. By submitting the copyright of their contributions under a copyleft license, they deliberately give up some of the rights that normally follow from copyright, including the right to be the unique distributor of copies of the work.
Some laws used for copyleft licenses vary from one country to another, and may also be granted in terms that vary from country to country. For example, in some countries, it is acceptable to sell a software product without warranty, while in most European countries it is not permitted for a software distributor to waive all warranties regarding a sold product. For this reason, the extent of such warranties is specified in most European copyleft licenses, such as the European Union Public Licence or the CeCILL license, that latter of which is a license that allows one to use GNU GPL code in combination with a limited warranty.
For projects which will be run over a network, a variation of the GNU GPL, called the Affero General Public License, ensures that the source code is available to users of software over a network.