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The "reversed c in a full circle" is the copyleft symbol. It is the copyright symbol turned in the left direction. Unlike the copyright symbol it has no legal meaning.

Copyleft is a play on the word copyright and is the practice of using copyright law to remove restrictions on distributing copies and modified versions of a work for others and require that the same freedoms be preserved in modified versions.

Copyleft is commonly implemented by a license and is applied to works such as computer software, documents, music, and art. Whereas copyright law, by default, automatically restricts the right to make and redistribute copies of an author's work, a copyleft license uses copyright law to ensure that every person who receives a copy of a work has the same rights to study, use, modify, and also redistribute both the work, and derived versions of the work. Such licenses typically do so by requiring that the same license terms apply to all redistributed versions of the work. The widest used and originating copyleft license is the GNU General Public License (GPL).

In a non-legal sense, copyleft is the opposite of copyright, by passing on the freedoms of copyright to all recipients of the work. In a legal sense, copyleft uses the right of the author to impose copyright restrictions with a copyright license on those who want to use the work in ways that require copyright. Under a copyleft form of copyright license, the restrictions imposed are that the work can be copied, modified or used in any subsequent work if, and only if, the author of that subsequent work agrees to grant the same copyleft rights to the public to freely copy, use and modify the subsequent work. For this reason copyleft licenses are also known as reciprocal licenses.

Authors use copyleft to allow anyone to use, share and improve the work as a continuing process, disallowing people from sharing derived works with any new restrictions. While copyleft is not a term in law, it is seen by proponents as a legal tool in a political and ideological debate over intellectual work. Some see copyleft as a first step in doing away with any kind of copyright law. Many fans of copyleft media believe that copyleft is a cross between copyright and public domain. In the public domain, the absence of copyleft-like protection leaves software in an unprotected state. Authors who use source code in the public domain can spread and sell binaries without providing the source code. If legal copyright was abolished and no other rights were provided there would be no means for copyleft licenses to exist. The need for copyleft would be diminished in such an environment, as it would become lawful for the community to disassemble and disseminate proprietary software as free software. However, there would be no way to preserve freedoms and rights for others or protect from propagations like software hoarding.


[edit] History

The concept of copyleft arose when Richard Stallman was working 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.[1]

As Stallman deemed it impractical in the short term to eliminate current copyright law and the wrongs he perceived it perpetuating, he decided to work within the framework of existing law; he created his own copyright license, the GNU General Public License (GPL), the first copyleft license. 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.[2]

The term copyleft, according to some sources, came from a message contained in Tiny BASIC, a freely distributed version of BASIC written by Dr. Li-Chen Wang in the late 1970s. The program listing contained the phrases "@COPYLEFT" and "ALL WRONGS RESERVED", puns on "copyright" and "all rights reserved", a phrase commonly used in copyright statements. Richard Stallman himself says the word comes from Don Hopkins, whom he calls a very imaginative fellow, who mailed him a letter in 1984 or 1985 on which was written: "Copyleft—all rights reversed." [3] The term "kopyleft" with the notation "All Rites Reversed" was also in use in the early 1970s within the Principia Discordia, which may have inspired Hopkins or influenced other usage. And in the arts Ray Johnson had earlier coined the term independently as it pertained to his making of and distribution of his mixed media imagery in his mail art and ephemeral gifts, for which he encouraged the making of derivative works [4] (While the phrase itself appears briefly as (or on) one of his pieces in the 2002 documentary How to Draw a Bunny, Johnson himself is not referenced in the 2001 documentary Revolution OS.)

There are definitional problems with the term "copyleft" which contribute to controversy over it. The term originated as an amusing back-formation from the term "copyright", and was originally a noun, meaning the copyright license terms of the GNU General Public License originated by Richard Stallman as part of the Free Software Foundation's work. Thus, "your program is covered by the copyleft" is almost considered to mean the same as the program being GPLed. When used as a verb, as in "he copylefted his most recent version", it is less precise and can refer to any of several similar licenses, or indeed a notional imaginary license for discussion purposes.

[edit] Applying copyleft

Common practice for using copyleft is to codify the copying terms for a work with a license. Any such license typically gives each person possessing a copy of the work the same freedoms as the author, including:

  1. the freedom to use and study the work,
  2. the freedom to copy and share the work with others,
  3. the freedom to change the work,
  4. and the freedom to distribute changed and therefore derivative works.

These freedoms do not ensure that a derivative work will be distributed under the same liberal terms. In order for the work to be truly copyleft, the license has to ensure that the author of a derived work can only distribute such works under the same or equivalent license.

In addition to restrictions on copying, copyleft licenses address other possible impediments. These include ensuring the rights cannot be later revoked and requiring the work and its derivatives are provided in a form that facilitates modification. In software, this requires that the source code of the derived work is made available.

Copyleft licenses necessarily make creative use of relevant rules and laws. 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, in standard GNU GPL style (see articles 11 and 12 of the GNU GPL license version 2), 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 are specified in most European copyleft licenses (see the CeCILL license, a license that allows one to use GNU GPL (see article 5.3.4 of CeCILL) in combination with a limited warranty (see article 9 of CeCILL).

[edit] Types of copyleft and relation to other licenses

See also: Free software licences#Freedom_preserving_restrictions

Copyleft is a distinguishing feature of some free software licenses. Copyleft even became a divisive issue in the ideological strife between the open source movement and the free software movement.[5] Many free software licenses are not copyleft licenses because they do not require the licensee to distribute derivative works under the same license. There is an ongoing debate as to which class of license provides the greater degree of freedom. This debate hinges on complex issues such as the definition of freedom and whose freedoms are more important, or whether to maximize the freedom of all potential future recipients of a work (freedom from the creation of proprietary software). Non-copyleft free software licenses maximize the freedom of the initial recipient (freedom to create proprietary software).

In common with the Creative Commons share-alike licensing system, GNU's Free Documentation License allows authors to apply limitations to certain sections of their work, exempting some parts of their creation from the full copyleft mechanism. In the case of the GFDL, these limitations include the use of invariant sections, which may not be altered by future editors. The initial intention of the GFDL was as a device for supporting the documentation of copylefted software. The result is however that it can be used for any kind of document.

[edit] Strong and weak copyleft

The copyleft governing a work is considered to be "stronger", to the extent that the copyleft provisions can be efficiently imposed on all kinds of derived works. "Weak copyleft" refers to licenses where not all derived works inherit the copyleft license; whether a derived work inherits or not often depends on the manner in which it was derived.

"Weak copyleft" licences are generally used for the creation of software libraries, to allow other software to link to the library, and then be redistributed without the legal requirement for the work to be distributed under the library's copyleft license. Only changes to the weak copylefted software itself become subject the copyleft provisions of such a license, not changes to the software that links to it. This allows programs of any license to be compiled and linked against copylefted libraries such as glibc (the GNU project's implementation of the C standard library), and then redistributed without any re-licensing required.

Two examples of free software licenses that use strong copyleft are the GNU General Public License and the Arphic Public License [6]. Free software licenses that use "weak" copyleft include the GNU Lesser General Public License (LGPL) [7] and the Mozilla Public License. Examples of non-copyleft free software licenses include the X11 license, Apache license and the BSD licenses.

The Design Science License is a strong copyleft license that can apply to any work that is not software, documentation, or art, such as music, sports photography, and video. It is hosted on the Free Software Foundation website's license list, but it is not considered compatible with the GPL by the Free Software Foundation.

[edit] Full and partial copyleft

"Full" and "partial" copyleft relate to another issue: Full copyleft is when all parts of a work (except the license itself) can be modified by consecutive authors. Partial copyleft exempts some parts of the work from the copyleft provisions, thus permitting unrestricted modification, or in some other way does not impose all the principles of copylefting on the work. For example, in artistic creation full copylefting is sometimes not possible or desirable (see below).

[edit] Share-alike

Many share-alike licenses are partial (or non-full) copyleft licenses. Share-alike, however, imposes the requirement that any freedom that is granted regarding the original work (or its copies), must be granted on exactly the same terms in any derived work: this further implies that any full copyleft license is automatically a share-alike license (but not the other way around!). Instead of using copyright's "all rights reserved" motto, or full copyleft's "all rights reversed", share-alike licenses rather use the "some rights reserved" statement. Some permutations of the Creative Commons licenses are examples of share-alike.

[edit] Is copyleft "viral"?

Copyleft licenses are sometimes referred to as viral copyright licenses, because any works derived from a copylefted work must themselves be copylefted when distributed. This language has been used by Microsoft <ref> </ref>. The term viral is used as an analogy of computer viruses. According to David Turner, it creates a misunderstanding and a fear of using copylefted free software.<ref>Brucy Byfield. 10 common misunderstandings about the GPL.[8]</ref>

Standard copyright programs can be considered "viral" by the same definition, since derivative works can only be distributed under terms imposed by the original author and require explicit permission. Such terms are more restrictive than any imposed by copyleft licenses.

Additionally, some popular copyleft licenses such as the GPL have a clause allowing components to interact with non-copyleft components as long as the communication is abstract, such as executing a command-line tool with a set of switches. As a consequence, even if one module of an otherwise non-copyleft product is placed under the GPL, it may still be legal for other components to communicate with it in a limited fashion.

[edit] See also


[edit] Notes and references


[edit] External links

ca:Copyleft cs:Copyleft da:Copyleft de:Copyleft el:Copyleft es:Copyleft eu:Copyleft fa:کپی‌لفت fr:Copyleft gl:Copyleft ko:카피레프트 hr:Copyleft id:Copyleft ia:Copyleft it:Copyleft he:Copyleft lt:Copyleft hu:Copyleft mk:Копилефт nl:Copyleft ja:コピーレフト no:Copyleft pl:Copyleft pt:Copyleft ru:Копилефт simple:Copyleft sr:Kopileft fi:Copyleft sv:Copyleft ta:அளிப்புரிமை th:Copyleft tr:Copyleft uk:Copyleft zh:Copyleft


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