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Copyleft is the practice of granting the right to freely distribute and modify
intellectual property Intellectual property (IP) is a category of property Property is a system of rights that gives people legal control of valuable things, and also refers to the valuable things themselves. Depending on the nature of the property, an owner o ...
with the requirement that the same rights be preserved in derivative works created from that property. Copyleft in the form of
license A license (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of variety (linguistics), varieties of the English language native to the United States. Cur ...

license
s can be used to maintain
copyright Copyright is a type of intellectual property Intellectual property (IP) is a category of property Property is a system of rights that gives people legal control of valuable things, and also refers to the valuable things themselves. ...

copyright
conditions for works ranging from
computer software Software is a collection of instructions Instruction or instructions may refer to: Computing * Instruction, one operation of a processor within a computer architecture instruction set * Computer program, a collection of instructions Music * I ...

computer software
, to
documents A document is a writing, written, drawing, drawn, presented, or memorialized representation of thought, often the manifestation of nonfiction, non-fictional, as well as fictional, content. The word originates from the Latin ''Documentum'', which ...

documents
,
art Art is a diverse range of (products of) human activities Humans (''Homo sapiens'') are the most populous and widespread species of primates, characterized by bipedality, opposable thumbs, hairlessness, and intelligence allowing the use ...

art
, scientific discoveries and even certain patents. Copyleft is an arrangement whereby software or artistic work may be used, modified, and distributed freely on condition that anything derived from it is bound by the same conditions. Copyleft
software licenses A software license is a legal instrument (usually by way of contract law A contract is a legally binding document between at least two parties that defines and governs the rights and duties of the parties to an agreement. A contract is legally ...
are considered ''protective'' or ''reciprocal'' in contrast with
permissive{{about, , the 1970 British film, Permissive (film), the grammatical mode, Permissive mood, the flavor of software license, permissive free software licence A permissive cell or host is one that allows a virus A virus is a submicroscopic i ...
free software Free software (or libre software) is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versions. Free software is a matter of liberty ...

free software
licenses, and require that information necessary for reproducing and modifying the work must be made available to recipients of the software program, or binaries. This information is most commonly in the form of
source code In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and ...

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 The GNU General Public License (GNU GPL or simply GPL) is a series of widely used free software license A free-software license is a notice that grants the recipient of a piece of software extensive rights to modify and software distribu ...
(GPL), originally written by
Richard Stallman Richard Matthew Stallman (; born March 16, 1953), also known by his initials, rms, is an American free software movement The free software movement is a social movement A social movement is a loosely organized effort by a large group of peo ...

Richard Stallman
, which was the first software copyleft license to see extensive use, the
Mozilla Public License The Mozilla Public License (MPL) is a free and open-source software license developed and maintained by the Mozilla Foundation. It is a weak copyleft license, characterized as a middle ground between permissive software licenses and the GNU Gen ...
, the
Free Art License The Free Art License (FAL), (french: Licence Art Libre (LAL)) is a copyleft Copyleft is the practice of granting the right to freely distribute and modify intellectual property Intellectual property (IP) is a category of property that incl ...
and the
Creative Commons Creative Commons (CC) is an American non-profit organization A nonprofit organization (NPO), also known as a non-business entity, not-for-profit organization, or nonprofit institution, is a legal entity organized and operated for a collect ...

Creative Commons
share-alike The copyleft.html"_;"title="Creative_Commons_icon_for_Share-Alike,_a_variant_of_the_copyleft">Creative_Commons_icon_for_Share-Alike,_a_variant_of_the_copyleft_symbol Share-alike_is_a_Copyright.html" ;"title="copyleft_symbol.html" ;"title="copylef ...
license condition, the last two of which being intended for other forms of intellectual and artistic work, such as documents and pictures.


History

An early use of the word ''copyleft'' was in
Li-Chen Wang ; All Wrongs Reserved in 1976 Li-Chen Wang (born 1935) is an American computer engineer, best known for his ''Palo Alto Tiny BASIC'' for Intel 8080 The Intel 8080 (''"eighty-eighty"'') is the second 8-bit microprocessor designed and manufactured ...
's Palo Alto
Tiny BASIC Tiny BASIC is a family of dialects The term dialect (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, kn ...
's distribution notice "@COPYLEFT ALL WRONGS RESERVED" in June 1976. 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 A BASIC interpreter is an interpreter that enables users to enter and run programs in the BASIC BASIC (Beginners' All-purpose Symbolic Instruction Code) is a family of General-purpose programming language, general-purpose, high-level programmin ...
. He encouraged others to adapt his source code and publish their adaptions, as with Roger Rauskolb's version of PATB published in ''
Interface Age ''Interface Age'', "published for the home computerist", was a computer magazine Computer magazines are about computers and related subjects, such as networking and the Internet. Most computer magazines offer (or offered) advice, some offer progr ...
''. The concept of copyleft was described in
Richard Stallman Richard Matthew Stallman (; born March 16, 1953), also known by his initials, rms, is an American free software movement The free software movement is a social movement A social movement is a loosely organized effort by a large group of peo ...

Richard Stallman
's ''
GNU Manifesto __NOTOC__ 235px, Richard M. Stallman (cover picture for Free as in Freedom'')">Free as in Freedom: Richard Stallman's Crusade for Free Software">Free as in Freedom'') The ''GNU Manifesto'' is a call-to-action by Richard Stallman Richard Mat ...
'' 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 Lisp (historically LISP) is a family of programming language A programming language is a formal language In logic, mathematics, computer science, and linguistics, a formal language consists of string (computer science), words whose symbo ...
interpreter.
Symbolics Symbolics is a defunct computer A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations automatically. Modern computers can perform generic sets of operations know ...
asked to use the Lisp interpreter, and Stallman agreed to supply them with a
public domain The public domain consists of all the creative work A creative work is a manifestation of creativity, creative effort including Work of art, fine artwork (sculpture, paintings, drawing, Sketch (drawing), sketching, performance art), dance, wr ...
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 Proprietary software, also known as non-free software or closed-source software, is computer software for which the software's publisher or another person reserves some rights from licenses to use, modify, share modifications, or share the softwa ...
, 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 wearing out. As Stallman deemed it impractical in the short term to eliminate current copyright law and the wrongs he perceived it perpetuated, he decided to work within the framework of existing
law Law is a system A system is a group of Interaction, interacting or interrelated elements that act according to a set of rules to form a unified whole. A system, surrounded and influenced by its environment, is described by its bounda ...
; 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 The GNU General Public License (GNU GPL or simply GPL) is a series of widely used free software license A free-software license is a notice that grants the recipient of a piece of software extensive rights to modify and software distribu ...
, 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 Don Hopkins is an artist An artist is a person engaged in an activity related to creating art, practicing the arts, or demonstrating an art. The common usage in both everyday speech and academic discourse refers to a practitioner in the visual a ...
, who mailed him a letter in 1984 or 1985, on which was written: "Copyleft – all rights reversed." In the early 1970s, the self-published book ''
Principia Discordia The ''Principia Discordia'' is a Discordian religious text Religious texts are texts related to a religious tradition. They differ from literary texts by being a compilation or discussion of beliefs, mythologies, ritual practices, commandmen ...
'' contains the notice "Ⓚ – reprint what you like" ''(
sic The Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in relation with ...

sic
)''. In the arts,
Ray Johnson Raymond Edward "Ray" Johnson (October 16, 1927 – January 13, 1995) was an American artist. Known primarily as a collagist and correspondence artist, he was a seminal figure in the history of Neo-Dada and early Pop art and was described as
had earlier coined the term independently as it pertained to his making of and distribution of his mixed media imagery in his
mail art Mail art, also known as postal art and correspondence art, is an artistic movement centered on sending small-scale works through the mail, postal service. It initially developed out of what eventually became Ray Johnson's New York Correspondence ...
and ephemeral gifts, for which he encouraged the making of
derivative work In copyright law Copyright is a type of intellectual property that gives its owner the exclusive right to make copies of a creative work, usually for a limited time. The creative work may be in a literary, artistic, educational, or musical ...
s. (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 ''Revolution OS'' is a 2001 documentary film that traces the twenty-year history of GNU, Linux, Open-source model, open source, and the free software movement. Directed by J. T. S. Moore, the film features interviews with prominent hacker (progra ...
''.) In
France France (), officially the French Republic (french: link=no, République française), is a transcontinental country This is a list of countries located on more than one continent A continent is one of several large landmasses ...

France
, a series of meetings taking place in 2000 under the title “Copyleft Attitude” gave birth to the
Free Art License The Free Art License (FAL), (french: Licence Art Libre (LAL)) is a copyleft Copyleft is the practice of granting the right to freely distribute and modify intellectual property Intellectual property (IP) is a category of property that incl ...
(FAL), theoretically valid in any jurisdiction bound by the
Berne Convention The Berne Convention for the Protection of Literary and Artistic Works, usually known as the Berne Convention, is an international agreement governing copyright, which was first accepted in Berne, Switzerland, in 1886. The Berne Convention form ...

Berne Convention
and recommended by Stallman’s own
Free Software Foundation The Free Software Foundation (FSF) is a 501(c)(3) A 501(c)(3) organization is a corporation, trust, unincorporated association, or other type of organization exempt from federal income tax under section 501(c)(3) of Title 26 of the United States ...
. Shortly thereafter, a separate, unrelated initiative in the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

United States
yielded the
Creative Commons license A Creative Commons (CC) license is one of several public copyright license A public license or public copyright licenses is a license by which a copyright holder as licensor can grant additional copyright permissions to any and all person ...
, 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


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/viewers of the work the freedom to carry out all of these activities. These freedoms (from the
Free Software Definition The Free Software Definition written by Richard Stallman Richard Matthew Stallman (; born March 16, 1953), also known by his initials, rms, is an American free software movement The free software movement is a social movement A social move ...
) include: ;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 ''The Open Source Definition'' is a document published by the Open Source Initiative, to determine whether a software license can be labeled with the Open-source software, open-source certification mark. The definition was taken from the exact te ...
, 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. 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.


Reciprocity

Instead of allowing a work to fall completely into the
public domain The public domain consists of all the creative work A creative work is a manifestation of creativity, creative effort including Work of art, fine artwork (sculpture, paintings, drawing, Sketch (drawing), sketching, performance art), dance, wr ...

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 Reciprocal may refer to: In mathematics * Multiplicative inverse, in mathematics, the number 1/''x'', which multiplied by ''x'' gives the product 1, also known as a ''reciprocal'' * Reciprocal polynomial, a polynomial obtained from another poly ...
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 Revocation is the act of wikt:recall, recall or annulment. It is the cancelling of an act, the recalling of a grant or privilege, or the making Void (law), void of some deed previously existing. A temporary revocation of a grant or privilege is ca ...
, and require the work and its derivatives to be provided in a form that allows further modifications to be made. In
software Software is a collection of instructions Instruction or instructions may refer to: Computing * Instruction, one operation of a processor within a computer architecture instruction set * Computer program, a collection of instructions Music * I ...

software
, this means requiring that the
source code In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and ...

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 sourced code and then adding extra restrictions to it, an action prevented by copyleft licensing the software. Some creators feel that preventing commercial enterprises from absorbing and selling their product is another incentive. Furthermore, the
open-source Open source is source code that is made freely available for possible modification and redistribution. Products include permission to use the source code, design documents, or content of the product. The open-source model is a decentralized softwar ...
culture of programming has been described as a gift culture, where social status 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 forego copyleft. The
Free Software Foundation The Free Software Foundation (FSF) is a 501(c)(3) A 501(c)(3) organization is a corporation, trust, unincorporated association, or other type of organization exempt from federal income tax under section 501(c)(3) of Title 26 of the United States ...
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 A license (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of variety (linguistics), varieties of the English language native to the United States. Cur ...

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 modified versions of that work. Unlike similar permissive licenses that also grant these freedoms, copyleft licenses also ensure that any modified versions of a copyleft licensed work must also grant these freedoms. Thus, copyleft licenses have restrictions: that modifications of any copyleft-licensed work 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 Fair use is a doctrine in the law of the United States that permits limited use of copyrighted material without having to first acquire permission from the copyright holder. Fair use is one of the limitations to copyright intended to balance the ...
, however, copyleft licenses may be superseded, just like regular copyrights. Therefore, any person utilizing a copyleft-licensed source for their own work 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, in standard GNU GPL style (see articles 11 and 12 o
the GNU GPL version 2
, while in most
Europe Europe is a continent A continent is any of several large landmass A landmass, or land mass, is a large region In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of scienc ...

Europe
an countries it is not permitted for a software distributor to
waive A waiver is the voluntary wikt:relinquishment, relinquishment or Surrender (law), surrender of some known Rights, right or privilege. Regulatory agencies of state departments or the federal government may issue waivers to exempt companies from c ...
all warranties regarding a sold product. For this reason the extent of such warranties are specified in most European copyleft licenses. Regarding that, see the European Union Public Licence EUPL, or the CeCILL license, a license that allows one to use GNU GPL (see article 5 of the EUPL and article 5.3.4 of CeCILL) in combination with a limited warranty (see article 7 and 8 of the EUPL and 9 of CeCILL). For projects which will be run over a network, a variation of the GPL is provided in the
Affero General Public License The Affero General Public License (Affero GPL and informally Affero License) is a free software license. The first version of the Affero General Public License (AGPLv1), was published by Affero, Inc. in March 2002, and based on the GNU General Pub ...
, which ensures that the source code is available to users of network software.


Types and relation to other licenses

Copyleft is a distinguishing feature of some
free software Free software (or libre software) is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versions. Free software is a matter of liberty ...

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 the creation of proprietary software) or just the initial recipient (freedom to create proprietary software). However, the current availability of both types of licenses, copyleft and permissive, allows authors to choose the type that best fits their work. For documents, art, and other works other than software and code, the
Creative Commons Creative Commons (CC) is an American non-profit organization A nonprofit organization (NPO), also known as a non-business entity, not-for-profit organization, or nonprofit institution, is a legal entity organized and operated for a collect ...

Creative Commons
share-alike licensing system and 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 Documentation is any communicable material that is used to describe, explain or instruct regarding some attributes of an object, system or procedure, such as its parts, assembly, installation, maintenance and use. Documentation can be provided on ...

documentation
of copylefted software. However, the result is that it can be used for any kind of document.


Strong and weak copyleft

The strength of the copyleft license governing a work is determined by the extent its provisions can be imposed on all kinds of derived works. Thus, the term "weak copyleft" refers to licenses where not all derived works inherit the copyleft license; whether a derived work inherits or not often depends on how it was derived. "Weak copyleft" licenses are often used to create software libraries. This allows other software to link to the library and be redistributed without the requirement for the linking software to also be copyleft-licensed. Only changes to the weak-copyleft-licensed software itself become subject to copyleft provisions of such a license. This allows programs of any license to be compiled and linked against copylefted libraries such as
glibc File:Linux kernel System Call Interface and glibc.svg, The GNU C Library is a wrapper around the system calls of the Linux kernel. The GNU C Library, commonly known as glibc, is the GNU Project's implementation of the C standard library. Des ...
and then redistributed without any re-licensing required. The concrete effect of strong vs. weak copyleft has yet to be tested in court. Free-software licenses that use "weak" copyleft include the
GNU Lesser General Public License The GNU Lesser General Public License (LGPL) is a free-software license published by the Free Software Foundation (FSF). The license allows developers and companies to use and integrate a software component released under the LGPL into their own ...
and the
Mozilla Public License The Mozilla Public License (MPL) is a free and open-source software license developed and maintained by the Mozilla Foundation. It is a weak copyleft license, characterized as a middle ground between permissive software licenses and the GNU Gen ...
. The most well-known free-software license using strong copyleft is the
GNU General Public License The GNU General Public License (GNU GPL or simply GPL) is a series of widely used free software license A free-software license is a notice that grants the recipient of a piece of software extensive rights to modify and software distribu ...
. A stronger copyleft license is the AGPL, which requires the publishing of the source code for
software as a service Software as a service (SaaS ) is a software licensing A software license is a legal instrument (usually by way of contract law A contract is a legally binding agreement that defines and governs the rights and duties between or among its P ...
use cases ("see also" the term sometimes used, "service as a software substitute
aaSS Aass Brewery (Norwegian: ''Aass Bryggeri'') is Norway Norway, officially the Kingdom of Norway,Names in the official and recognised languages: Bokmål Bokmål (, ; literally "book tongue") is an official written standard for the Norw ...
) e.g. when software is deployed on servers.List of free-software licences on the GNU website
"''We recommend that developers consider using the GNU AGPL for any software which will commonly be run over a network''".
The
Sybase Open Watcom Public License The Sybase Open Watcom Public Licence is a software license that has been approved by the Open Source Initiative. It is the Software license, licence under which the Open Watcom C/C++ compiler is released. The license has not been accepted as "fre ...
is one of the strongest copyleft licenses, as this license closes the "private usage" loophole of the GPL, and requires the publishing of source code in any use case. A final, notable strong copyleft license is the Design Science License, as it can apply to any work, not only software or documentation, but also literature, artworks, music, photography and video. The Design Science License was created by Michael Stutz after he took an interest in applying GNU-style copyleft to non-software works, which later came to be called
open content Free content, libre content, or free information is any kind of functional work, work of art, or other creative Content (media and publishing), content that meets the definition of a Definition of Free Cultural Works, free cultural work. De ...

open content
. In the 1990s the DSL was used on music recordings, visual art, and even novels. It is now hosted on the Free Software Foundation website's license list, but it is not considered compatible with the GPL by the Free Software Foundation.


Full and partial copyleft

"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.


Share-alike

The "
share-alike The copyleft.html"_;"title="Creative_Commons_icon_for_Share-Alike,_a_variant_of_the_copyleft">Creative_Commons_icon_for_Share-Alike,_a_variant_of_the_copyleft_symbol Share-alike_is_a_Copyright.html" ;"title="copyleft_symbol.html" ;"title="copylef ...
" 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 creator, but that the author will be recognized and hold equal claim over the changed code. Some Creative Commons licenses are examples of share-alike copyleft licenses.


Permissive licenses

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, MIT license and the
BSD licenses BSD licenses are a family of permissive free software license A permissive software license, sometimes also called BSD-like or BSD-style license, is a free-software license with only minimal restrictions on how the software can be used, mod ...
.


Debate and controversy

It has been suggested that copyleft became a divisive issue in the ideological strife between the
Open Source Initiative The Open Source Initiative (OSI) is the steward of the Open Source Definition ''The Open Source Definition'' is a document published by the Open Source Initiative, to determine whether a software license can be labeled with the Open-source soft ...
and the
free-software movement The free software movement is a social movement with the goal of obtaining and guaranteeing certain freedoms for software users, namely the freedoms to run the software, to study the software, to modify the software, and to share copies of the so ...
. 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. * 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" license. * Some of the software programs of the GNU Project are published under non-copyleft licenses. * Stallman himself has endorsed the use of non-copyleft licenses in certain circumstances, most recently in the case of the
Ogg Vorbis Vorbis is a free and open-source software Free and open-source software (FOSS) is software Software is a collection of instructions that tell a computer A computer is a machine that can be programmed to carry out sequences of ari ...
license change.


Viral licensing

''Viral license'' is a pejorative name for copyleft licenses. 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. The name " viral licenses" refers to the fact that any works derived from a copyleft work must preserve the copyleft permissions when distributed. Some
BSD License BSD licenses are a family of permissive free software licenses, imposing minimal restrictions on the use and distribution of covered software. This is in contrast to copyleft Copyleft is the practice of granting the right to freely distrib ...
advocates 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.
Microsoft Microsoft Corporation is an American multinational corporation, multinational technology company, technology corporation which produces Software, computer software, consumer electronics, personal computers, and related services. Its best-know ...

Microsoft
vice-president
Craig Mundie Craig James Mundie (born July 1, 1949 in Cleveland, Ohio Cleveland ( ), officially the City of Cleveland, is a major city in the U.S. state of Ohio, and the county seat of Cuyahoga County. It is located along the southern shore of Lake E ...
remarked, "This viral aspect of the GPL poses a threat to the intellectual property of any organization making use of it." In another context,
Steve Ballmer Steven Anthony Ballmer (; March 24, 1956) is an American businessman and investor who served as the chief executive officer A chief executive officer (CEO), chief administrator officer, or just chief executive (CE), is one of a number of corporat ...

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 touches". In response to Microsoft's attacks on the GPL, several prominent free-software developers and advocates released a joint statement supporting the license. According to FSF compliance engineer David Turner, the term "viral license" creates a misunderstanding and a fear of using copylefted free software. While a person can catch a virus without active action, license conditions take effect upon effective usage or adoption. 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." 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 , not like a virus." 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 or interacting with a Web server. 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 normally. This allowed communication may or may not include reusing libraries or routines via
dynamic linking In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and softwar ...
 – some commentators say it does, the FSF asserts it does not and explicitly adds an exception allowing it in the license for the
GNU Classpath GNU Classpath is a free software Free software (or libre software) is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versions. Free ...
re-implementation of the Java library. This ambiguity is an important difference between the GPL and the
LGPL The GNU Lesser General Public License (LGPL) is a free-software license published by the Free Software Foundation (FSF). The license allows developers and companies to use and integrate a software component released under the LGPL into their own ...
, in that the LGPL specifically allows linking or compiling with the covered work.Stallman, Richard
Why you shouldn't use the Lesser GPL for your next library
GNU Project The GNU Project () is a free software Free software (or libre software) is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versi ...


Symbol

The copyleft symbol is a mirror image of the
copyright symbol The copyright symbol, or copyright sign, (a circled capital letter C for copyright Copyright is a type of intellectual property that gives its owner the exclusive right to make copies of a creative work, usually for a limited time. The c ...

copyright symbol
, : a reversed in a circle. It has no legal status. A 2016 proposal to add the symbol to a future version of Unicode was accepted by the
Unicode Technical Committee The Unicode Consortium (legally Unicode, Inc.) is a 501(c)(3) non-profit organization incorporated and based in Mountain View, California, Mountain View, California. Its primary purpose is to maintain and publish the Unicode Standard which was deve ...
. The code point was added in Unicode 11. it is largely unimplemented in fonts, but can be approximated with character or the more widely available character between parenthesis or, if supported by the application or web browser, by combining a reversed c with the character : . ''For a list of fonts that include this glyph, see Unicode fonts#List of SMP Unicode fonts and then row "
Enclosed Alphanumeric Supplement Enclosed Alphanumeric Supplement is a Unicode block consisting Latin alphabet characters and Arabic numerals enclosed in circles, ovals or boxes, used for a variety of purposes. It is encoded in the range U+1F100–U+1F1FF in the Supplement ...
(173: 1F100–1F1FF)" (This list is not guaranteed to be current).''


See also

* *
All rights reversed 100px, The copyleft symbol. Unlike the copyright symbol, it has no legal meaning. All rights reversed is a phrase that indicates a release of copyright Copyright is a type of intellectual property that gives its owner the exclusive right ...

All rights reversed
*
Anti-copyright notice An anti-copyright notice is a specific statement that is added to a work in order to encourage wide distribution. Such notices are legally required to host such specific media; under the Berne Convention in international copyright law, works are ...
*
Commercial use of copyleft works Commerce, Commercial advantage of copyleft works differs from Intellectual property rights#Economic view, traditional commercial advantage of Intellectual Property Rights (IPR). The economic focus tends to be on monetizing other scarcities, complim ...
* Comparison of open source and closed source *
Copyright Copyright is a type of intellectual property Intellectual property (IP) is a category of property Property is a system of rights that gives people legal control of valuable things, and also refers to the valuable things themselves. ...

Copyright
* Creative Commons licences *
Free Art License The Free Art License (FAL), (french: Licence Art Libre (LAL)) is a copyleft Copyleft is the practice of granting the right to freely distribute and modify intellectual property Intellectual property (IP) is a category of property that incl ...
* Free content * Free Culture movement * Free-software movement *
GNU General Public License The GNU General Public License (GNU GPL or simply GPL) is a series of widely used free software license A free-software license is a notice that grants the recipient of a piece of software extensive rights to modify and software distribu ...
* Hacktivismo Enhanced-Source Software License Agreement, HESSLA – a license which prohibits uses that violate human rights or add spyware * History of free and open-source software * Piratbyrån#Kopimi, Kopimi * Open content * Open source * Opposition to copyright * Patentleft * Permissive software licence, Permissive free-software licence * Public copyright license * Public domain * Share-alike


References


External links


What is copyleft?
– by
Richard Stallman Richard Matthew Stallman (; born March 16, 1953), also known by his initials, rms, is an American free software movement The free software movement is a social movement A social movement is a loosely organized effort by a large group of peo ...

Richard Stallman

Copyleft: Pragmatic Idealism
– by Richard Stallman {{Intellectual property activism Copyleft, Copyright law Free software Intellectual property activism Free and open-source software licenses Typographical symbols