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Copyleft
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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
Copyleft
Articles on copyleft licensing
Topics
* 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
nature.
[ ]
Contents
* 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
History[edit]
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]
Freedom[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)
include:^[10]^[17]
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.
Reciprocity[edit]
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
opportunities.^[21]
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
symbol
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.
Share-alike[edit]
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"
license.^[39]
* 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
touches".^[54]
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
LGPL.^[62]
Symbol[edit]
<?>
You may need rendering support to display the uncommon Unicode
characters in this section correctly.
(c)
Copyleft symbol
In Unicode U+1F12F
🄯 COPYLEFT SYMBOL
Alternative symbol: (O)
Different from
Different from U+00A9
(c) COPYRIGHT SIGN
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
U+1F12F
🄯 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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2.0; BY LI-CHEN WANG; MODIFIED AND TRANSLATED TO INTEL MNEMONICS;
BY ROGER RAUSKOLB; 10 OCTOBER, 1976; @COPYLEFT; ALL WRONGS
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BY ROGER RAUSKOLB; 10 OCTOBER, 1976; @COPYLEFT; ALL WRONGS
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