Permissive free software licence
Encyclopedia
A permissive free software licence is a class of free software licence
with minimal requirements about how the software can be redistributed. This is in contrast to copyleft
licences, which have reciprocity / share-alike requirements. Both sets of free software licences offer the same freedoms in terms of how the software can be used, studied, and privately modified. A major difference is that when the software is being redistributed (either modified or unmodified), permissive licences permit the redistributor to combine the licensed material with other license terms, potentially adding further restrictions to a derived work, while copyleft licences do not allow further restrictions (among other possible differences). The term "permissive" as applied to software licensing is sometimes debatable in terms of specific terms and requirements, with occasional references to very weakly copyleft as "permissive". A more narrowly constrained term related to permissive licensing is copyfree, which implies distinct license term requirements analogous to, but different from, those of free software
.
Well-known examples of permissive free software licences include the MIT License
, the BSD licences and the GNU Lesser General Public License
. A well known copyleft licence is the GNU General Public License
.
Permissive licences often do stipulate some limited requirements, such as that the original authors must be credited (attribution). If a work is truly in the public domain, this is usually not legally required, but a United States copyright registration requires disclosing material that has been previously published, and attribution may still be considered an ethical requirement in academia.
famous for his work on BSD, during one of his speeches at BSDCon 1999. It is a word play
on copyright
, copyleft
and copy center.
The liberty to 'make as many copies as you want' is in fact provided by all copyleft licenses. However, unlike both copyleft licences and copyright law, permissive free software licences do not control the licence terms that a derivative work falls under. Nevertheless, the quote describes the permissive licence users' unconcern for the discussion on freedoms.
, and the OpenSSL Licence. These licences, although they are permissive free software licences, are incompatible with the widely used GNU General Public License
.
Examples of permissive free software licences without advertising clauses are the MIT License
, the 3-clause BSD license, the Zlib License
, and all versions of the Apache License
except 1.0.
Some licences do not allow derived works to add a restriction that says a redistributor cannot add more restrictions. The purpose of such clauses is to disallow redistribution using the GPL or similar copyleft licences. There are many examples such as the CDDL
and MsPL. However such restrictions also make the licence incompatible with the BSD licences.
Free software licence
A free software licence is a software licence which grants recipients rights to modify and redistribute the software, which would otherwise be prohibited by copyright law. A free software licence grants, to the recipients, freedoms in the form of permissions to modify or distribute copyrighted work...
with minimal requirements about how the software can be redistributed. This is in contrast to copyleft
Copyleft
Copyleft is a play on the word copyright to describe the practice of using copyright law to offer the right to distribute copies and modified versions of a work and requiring that the same rights be preserved in modified versions of the work...
licences, which have reciprocity / share-alike requirements. Both sets of free software licences offer the same freedoms in terms of how the software can be used, studied, and privately modified. A major difference is that when the software is being redistributed (either modified or unmodified), permissive licences permit the redistributor to combine the licensed material with other license terms, potentially adding further restrictions to a derived work, while copyleft licences do not allow further restrictions (among other possible differences). The term "permissive" as applied to software licensing is sometimes debatable in terms of specific terms and requirements, with occasional references to very weakly copyleft as "permissive". A more narrowly constrained term related to permissive licensing is copyfree, which implies distinct license term requirements analogous to, but different from, those of free software
Free software
Free software, software libre or libre software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions that only ensure that further recipients can also do...
.
Well-known examples of permissive free software licences include the MIT License
MIT License
The MIT License is a free software license originating at the Massachusetts Institute of Technology . It is a permissive license, meaning that it permits reuse within proprietary software provided all copies of the licensed software include a copy of the MIT License terms...
, the BSD licences and the GNU Lesser General Public License
GNU Lesser General Public License
The GNU Lesser General Public License or LGPL is a free software license published by the Free Software Foundation . It was designed as a compromise between the strong-copyleft GNU General Public License or GPL and permissive licenses such as the BSD licenses and the MIT License...
. A well known copyleft licence is the GNU General Public License
GNU General Public License
The GNU General Public License is the most widely used free software license, originally written by Richard Stallman for the GNU Project....
.
Comparison to public domain
Computer Associates Int'l v. Altai used the term "public domain" to refer to works that have become widely shared and distributed under permission, rather than work that was deliberately put into the public domain. However, such licences are not actually equivalent to releasing a work into the public domain.Permissive licences often do stipulate some limited requirements, such as that the original authors must be credited (attribution). If a work is truly in the public domain, this is usually not legally required, but a United States copyright registration requires disclosing material that has been previously published, and attribution may still be considered an ethical requirement in academia.
Comparison to Copyleft
Copyleft is "a general method for making a program or other work free, and requiring all modified and extended versions of the program to be free as well." By comparison with permissive licences, copyleft licensing places more restrictions and demands in terms of distribution and combination with other licences.Other terms
Copycenter is a term originally used to explain the modified BSD license, a permissive free software licence. The term was presented by Kirk McKusick, a computer scientistComputer scientist
A computer scientist is a scientist who has acquired knowledge of computer science, the study of the theoretical foundations of information and computation and their application in computer systems....
famous for his work on BSD, during one of his speeches at BSDCon 1999. It is a word play
Word play
Word play or wordplay is a literary technique in which the words that are used become the main subject of the work, primarily for the purpose of intended effect or amusement...
on copyright
Copyright
Copyright is a legal concept, enacted by most governments, giving the creator of an original work exclusive rights to it, usually for a limited time...
, copyleft
Copyleft
Copyleft is a play on the word copyright to describe the practice of using copyright law to offer the right to distribute copies and modified versions of a work and requiring that the same rights be preserved in modified versions of the work...
and copy center.
The liberty to 'make as many copies as you want' is in fact provided by all copyleft licenses. However, unlike both copyleft licences and copyright law, permissive free software licences do not control the licence terms that a derivative work falls under. Nevertheless, the quote describes the permissive licence users' unconcern for the discussion on freedoms.
Copyleft Compatibility
Some permissive free software licences contain clauses that require advertising materials to credit the copyright holder. Licences with an advertising clause include the 4-clause BSD licence, the PHP LicensePHP License
The PHP License is the software license under which the PHP scripting language is released. The PHP License is a non-copyleft free software license according to the Free Software Foundation and an open source license according to the Open Source Initiative...
, and the OpenSSL Licence. These licences, although they are permissive free software licences, are incompatible with the widely used GNU General Public License
GNU General Public License
The GNU General Public License is the most widely used free software license, originally written by Richard Stallman for the GNU Project....
.
Examples of permissive free software licences without advertising clauses are the MIT License
MIT License
The MIT License is a free software license originating at the Massachusetts Institute of Technology . It is a permissive license, meaning that it permits reuse within proprietary software provided all copies of the licensed software include a copy of the MIT License terms...
, the 3-clause BSD license, the Zlib License
Zlib License
The zlib License is a permissive free software license which defines the terms under which the zlib and libpng software libraries can be distributed. It is also used by other free software packages....
, and all versions of the Apache License
Apache License
The Apache License is a copyfree free software license authored by the Apache Software Foundation . The Apache License requires preservation of the copyright notice and disclaimer....
except 1.0.
Some licences do not allow derived works to add a restriction that says a redistributor cannot add more restrictions. The purpose of such clauses is to disallow redistribution using the GPL or similar copyleft licences. There are many examples such as the CDDL
Common Development and Distribution License
Common Development and Distribution License is a free software license, produced by Sun Microsystems, based on the Mozilla Public License , version 1.1....
and MsPL. However such restrictions also make the licence incompatible with the BSD licences.
See also
- Free software licenceFree software licenceA free software licence is a software licence which grants recipients rights to modify and redistribute the software, which would otherwise be prohibited by copyright law. A free software licence grants, to the recipients, freedoms in the form of permissions to modify or distribute copyrighted work...
- Comparison of free software licences
- List of FSF approved software licences
- List of OSI approved software licences