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   Practice of mandating free use in all derivatives of a work

   Small letter c turned 180 degrees, surrounded by a single line forming
   a circle.
   Copyleft symbol
   Articles on copyleft licensing
     * Copyleft
     * Open-source license
     * Free-software license
     * Free and open-source software
     * Royalty-free

   Higher categories: Software, freedom
     * Category:Free and open-source
       software licenses

     * v
     * t
     * e

   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, scientific
   discoveries and even certain patents.^[1]

   Copyleft software licenses are considered protective or reciprocal in
   contrast with permissive free software licenses,^[2] and require that
   information necessary for reproducing and modifying the work must be
   made available to recipients of the software program, which are often
   distributed as binary executables. 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.

   Notable copyleft licenses include the GNU General Public License (GPL),
   originally written by Richard Stallman, which was the first software
   copyleft license to see extensive use,^[3] the Mozilla Public License,
   the Free Art License,^[4] and the Creative Commons share-alike license
   condition,^[5] with the last two being intended for other types of
   works, such as documents and pictures, both academic or artistic in
   [ ]


     * 1 History
     * 2 Copyleft principles
          + 2.1 Freedom
          + 2.2 Reciprocity
          + 2.3 Economic incentive
     * 3 Copyleft application
     * 4 Types and relation to other licenses
          + 4.1 Strong and weak copyleft
          + 4.2 Full and partial copyleft
          + 4.3 Share-alike
          + 4.4 Permissive licenses
     * 5 Debate and controversy
          + 5.1 Viral licensing
     * 6 Symbol
     * 7 See also
     * 8 References


   An early use of the word copyleft was in Li-Chen Wang's Palo Alto Tiny
   BASIC's distribution notice "@COPYLEFT ALL WRONGS RESERVED" in June
   1976.^[6]^[7] Tiny BASIC was not distributed under any formal form of
   copyleft distribution terms, but it was presented in a context where
   source code was being shared and modified. In fact, Wang had earlier
   contributed edits to Tiny BASIC Extended before writing his own BASIC
   interpreter.^[8] He encouraged others to adapt his source code and
   publish their adaptions, as with Roger Rauskolb's version of PATB
   published in Interface Age.^[9]

   The concept of copyleft was described in Richard Stallman's GNU
   Manifesto in 1985, where he wrote:

     GNU is not in the public domain. Everyone will be permitted to
     modify and redistribute GNU, but no distributor will be allowed to
     restrict its further redistribution. That is to say, proprietary
     modifications will not be allowed. I want to make sure that all
     versions of GNU remain free.

   Stallman worked a few years earlier 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.^[10]^[11]

   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,^[12] he
   created his own copyright license, the Emacs General Public
   License,^[13] 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.^[14]
   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".^[14] In the early 1970s, the
   self-published book Principia Discordia contains the notice "K-o All
   Rites Reversed - reprint what you like" (sic). 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. (While the phrase 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.)

   In France, a series of meetings taking place in 2000 under the title
   "Copyleft Attitude" gave birth to the Free Art License (FAL),^[15]
   theoretically valid in any jurisdiction bound by the Berne Convention
   and recommended by Stallman's own Free Software Foundation.^[16]
   Shortly thereafter, a separate, unrelated initiative in the United
   States yielded the Creative Commons license, available since 2001 in
   several different versions (only some of which can be described as
   copyleft) and more specifically tailored to U.S. law.

Copyleft principles[edit]


   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. These freedoms (from the Free Software Definition)

   Freedom 0
          the freedom to use the work

   Freedom 1
          the freedom to study the work

   Freedom 2
          the freedom to copy and share the work with others

   Freedom 3
          the freedom to modify the work, and the freedom to distribute
          modified and therefore derivative works

   Similar terms are present in the Open Source Definition, a separate
   definition that contains similar freedoms. The vast majority of
   copyleft licenses satisfy both definitions, that of the Free Software
   Definition and Open Source Definition.^[10] By guaranteeing viewers and
   users of a work the freedom and permission to reproduce, adapt, or
   distribute it, copyleft licenses are distinct from other types of
   copyright licenses that limit such freedoms.


   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.^[10]

   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.^[18]

   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.^[10]

Economic incentive[edit]

   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,^[19]
   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 culture, where social power is determined by an individual's
   contributions.^[20] 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

   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.^[22] 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",^[23] allowing the code to be copied and used freely is more
   important than a copyleft.

Copyleft application[edit]

   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.^[24]^[25]

   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 (or
   none at all) provided they meet the fair use standard.^[26]

   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.^[citation needed] 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 General Public License style, while
   in most European countries it is not permitted for a software
   distributor to waive all warranties regarding a sold product.^[citation
   needed] For this reason, the extent of such warranties is specified in
   most European copyleft licenses, for example, the European Union Public
   Licence (EUPL),^[27] or the CeCILL license,^[28] a license that allows
   one to use GNU GPL 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 (GNU AGPL), ensures that
   the source code is available to users of software over a network.

Types and relation to other licenses[edit]

   See also: Free-software licence S: Restrictions
   Free Non-free
   Public domain & equivalents Permissive license Copyleft (protective
   license) Noncommercial license Proprietary license Trade secret
   Description Grants all rights Grants use rights, including right to
   relicense (allows proprietization, license compatibility) Grants use
   rights, forbids proprietization Grants rights for noncommercial use
   only. May be combined with share-alike. Traditional use of copyright;
   certain rights may or may not be granted No information made public
   For software PD, Unlicense, CC0 BSD, MIT, Apache GPL, AGPL JRL, AFPL
   Proprietary software, no public license Private, internal software
   For other creative works PD, CC0 CC-BY CC-BY-SA, FAL CC-BY-NC
   Copyright, no public license Unpublished
   The Creative Commons icon for Share-Alike, a variant of the copyleft

   Copyleft is a distinguishing feature of some free software licenses,
   while other 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: the potential future recipients of a work (freedom
   from proprietization) or just the initial recipient (freedom to
   proprietize). However, current copyright law and the availability of
   both types of licenses, copyleft and permissive, allow authors to
   choose the type under which to license the works they invent.

   For documents, art, and other works other than software and code, the
   Creative Commons share-alike licensing system and the GNU Free
   Documentation License (GFDL) allow authors to apply limitations to
   certain sections of their work, exempting some parts of the work 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. However, the
   result is that it can be used for any kind of document.

Strong and weak copyleft[edit]

   The strength of the copyleft license governing a work is determined by
   the extent to its provisions can be imposed on all kinds of derivative
   works. Thus, the term "weak copyleft" refers to licenses where not all
   derivative works inherit the copyleft license; whether a derivative
   work inherits or not often depends on how it was derived.

   "Weak copyleft" licenses are often used to cover software libraries.
   This allows other software to link to the library and be redistributed
   without the requirement for the linking software to also be licensed
   under the same terms. Only changes to the software licensed under a
   "weak copyleft" license become subject itself to copyleft provisions of
   such a license. This allows programs of any license to be compiled and
   linked against copylefted libraries such as glibc and then
   redistributed without any re-licensing required. The concrete effect of
   strong vs. weak copyleft has yet to be tested in court.^[29]
   Free-software licenses that use "weak" copyleft include the GNU Lesser
   General Public License and the Mozilla Public License.

   The GNU General Public License is an example of a license implementing
   strong copyleft. A stronger copyleft license is the AGPL, which
   requires the publishing of the source code for software as a service
   use cases.^[30]^[31]^[32]^[33]

   The Sybase Open Watcom Public License is one of the strongest copyleft
   licenses, as this license closes the so-called "private usage" loophole
   of the GPL, and requires the publishing of source code in any use case.
   For this reason, the license is considered non-free by the Free
   Software Foundation, the GNU Project, and the Debian project.^[34]
   However, the license is accepted as open source by the OSI.

   The Design Science License (DSL) is a strong copyleft license that
   applies to any work, not only software or documentation, but also
   literature, artworks, music, photography, and video. DSL was written by
   Michael Stutz after he took an interest in applying GNU-style copyleft
   to non-software works, which later came to be called libre works. In
   the 1990s, it was used on music recordings, visual art, and even
   novels. It is not considered compatible with the GNU GPL by the Free
   Software Foundation.^[35]

Full and partial copyleft[edit]

   "Full" and "partial" copyleft relate to another issue. Full copyleft
   exists when all parts of a work (except the license itself) may only be
   modified and distributed under the terms of the work's copyleft
   license. Partial copyleft, by contrast, exempts some parts of the work
   from the copyleft provisions, permitting distribution of some
   modifications under terms other than the copyleft license, or in some
   other way does not impose all the principles of copylefting on the
   work. An example of partial copyleft is the GPL linking exception made
   for some software packages.


   The "share-alike" condition in some licenses imposes the requirement
   that any freedom that is granted regarding the original work must be
   granted on exactly the same or compatible terms in any derived work.

   This implies that any copyleft license is automatically a share-alike
   license but not the other way around, as some share-alike licenses
   include further restrictions such as prohibiting commercial use.
   Another restriction is that not everyone wants to share their work and
   some share-alike agreements require that the whole body of work be
   shared, even if the author only wants to share a certain part. The plus
   side for an author of source code is that any modification to the code
   will not only benefit the original author but that the author will be
   recognized and ensure the same or compatible license terms cover the
   changed code.^[36] Some Creative Commons licenses are examples of
   share-alike copyleft licenses.

Permissive licenses[edit]

   Permissive software licenses are those that grant users of the software
   the same freedoms as copyleft licenses but do not require modified
   versions of that software to also include those freedoms. They have
   minimal restrictions on how the software can be used, modified, and
   redistributed, and are thus not copyleft licenses. Examples of this
   type of license include the X11 license, Apache license, Expat license,
   and the various BSD licenses.

Debate and controversy[edit]

   It has been suggested that copyleft has become a divisive issue in the
   ideological strife between the Open Source Initiative and the free
   software movement.^[37] However, there is evidence that copyleft is
   both accepted and proposed by both parties:
     * Both the OSI and the FSF have copyleft and non-copyleft licenses in
       their respective lists of accepted licenses.^[38]^[35]
     * The OSI's original Legal Counsel Lawrence Rosen has written a
       copyleft license, the Open Software License.
     * The OSI's licensing how-to recognises the GPL as a "best practice"
     * Some of the software programs of the GNU Project are published
       under non-copyleft licenses.^[40]
     * Stallman himself has endorsed the use of non-copyleft licenses in
       certain circumstances, most recently in the case of the Ogg Vorbis
       license change.^[41]

Viral licensing[edit]

   Main article: Viral license

   Viral license is a pejorative name for copyleft
   licenses.^[42]^[43]^[44]^[45]^[46] It originates from the terms
   'General Public Virus' or 'GNU Public Virus' (GPV), which dates back to
   1990, a year after the GPLv1 was released.^[47]^[48]^[49] The name
   "viral licenses" refers to the fact that any works derived from a
   copyleft work must preserve the copyleft permissions when distributed.

   Some advocates of the various BSD Licenses used the term derisively in
   regards to the GPL's tendency to absorb BSD-licensed code without
   allowing the original BSD work to benefit from it, while at the same
   time promoting itself as "freer" than other licenses.^[50]^[51]^[52]
   Microsoft vice-president Craig Mundie remarked, "This viral aspect of
   the GPL poses a threat to the intellectual property of any organization
   making use of it."^[53] In another context, Steve Ballmer declared that
   code released under GPL is useless to the commercial sector, since it
   can only be used if the resulting surrounding code is licensed under a
   GPL-compatible license, and described it thus as "a cancer that
   attaches itself in an intellectual property sense to everything it

   In response to Microsoft's attacks on the GPL, several prominent
   free-software developers and advocates released a joint statement
   supporting the license.^[55] According to FSF compliance engineer David
   Turner, the term "viral license" creates a misunderstanding and a fear
   of using copylefted free software.^[56] While a person can catch a
   virus without active action, license conditions take effect upon
   effective usage or adoption.^[57] David McGowan has also written that
   there is no reason to believe the GPL could force proprietary software
   to become free software, but could "try to enjoin the firm from
   distributing commercially a program that combined with the GPL'd code
   to form a derivative work, and to recover damages for infringement." If
   the firm "actually copied code from a GPL'd program, such a suit would
   be a perfectly ordinary assertion of copyright, which most private
   firms would defend if the shoe were on the other foot."^[58] Richard
   Stallman has described this view with an analogy, saying, "The GPL's
   domain does not spread by proximity or contact, only by deliberate
   inclusion of GPL-covered code in your program. It spreads like a spider
   plant, not like a virus."^[59]

   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,^[failed verification] such as executing a
   command-line tool with a set of switches or interacting with a web
   server.^[60] 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 ways such as
   these.^[clarification needed] This allowed communication may or may not
   include reusing libraries or routines via dynamic linking - some
   commentators say it does,^[61] the FSF asserts it does not and
   explicitly adds an exception allowing it in the license for the GNU
   Classpath re-implementation of the Java library. This ambiguity is an
   important difference between the GPL and the LGPL, in that the LGPL
   specifically allows linking or compiling works licensed under terms
   that are not compatible with the LGPL, with works covered by the


   You may need rendering support to display the uncommon Unicode
   characters in this section correctly.

      Copyleft symbol
     In Unicode   U+1F12F
   Alternative symbol: (O)
       Different from
   Different from U+00A9

   The copyleft symbol is a mirror image of the copyright symbol, (c): a
   reversed C in a circle. It has no legal status.^[63] A 2016
   proposal^[64] to add the symbol to a future version of Unicode was
   accepted by the Unicode Technical Committee.^[65] The code point
   🄯 COPYLEFT SYMBOL was added in Unicode 11.^[65]^[66]

   As of 2018,^[update] it is largely unimplemented in fonts, but can be
   approximated with character U+2184
   ↄ LATIN SMALL LETTER REVERSED C or the more widely available
   character U+0254 O LATIN SMALL LETTER OPEN O between parenthesis (O)
   or, if supported by the application or web browser, by combining a
   reversed c with the character U+20DD ⃝ COMBINING ENCLOSING
   CIRCLE: .^[67]

   For a list of fonts that include this glyph, see Unicode fonts S: List
   of SMP Unicode fonts and then row "Enclosed Alphanumeric Supplement
   (173: 1F100-1F1FF)" (This list is not guaranteed to be current).

See also[edit]

     * Free and open-source software portal

     * List of copyleft software licenses
     * All rights reversed
     * Anti-copyright notice
     * Commercial use of copyleft works
     * Comparison of open source and closed source
     * Copyfraud
     * Copyright
     * Copyright alternatives
     * Creative Commons licenses
     * Criticism of intellectual property
     * Internet freedom
     * Free Art License
     * Free content
     * Free Culture movement
     * Free software movement
     * GNU General Public License
     * HESSLA - a license that prohibits uses that violate human rights or
       add spyware
     * History of free and open-source software
     * Kopimi
     * Open content
     * Open source
     * Opposition to copyright
     * Patentleft
     * Permissive free-software licence
     * Public copyright license
     * Public domain
     * Share-alike
     * Steal This Film


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