Permissive free software licence
A permissive software license is a class of FOSS software license with minimal requirements about how the software can be redistributed. Well-known examples of permissive free software licenses include the MIT License and the BSD licenses. As of 2015, the most popular FOSS license is the permissive MIT license.
The OSI defines a permissive software license plainly as a "non-copyleft license". GitHub's choosealicense website described the MIT permissive license as "lets people do anything they want with your code as long as they provide attribution back to you and don’t hold you liable."
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 scientist 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 way it was characterized politically, you had copyright, which is what the big companies use to lock everything up; you had copyleft, which is free software's way of making sure they can't lock it up; and then Berkeley had what we called ‘copycenter’, which is ‘take it down to the copy center and make as many copies as you want.’
The liberty to 'make as many copies as you want' is in fact also provided by all copyleft licences. However, unlike both copyleft licences and copyright law, permissive free software licences do not control the licence terms that a derivative work falls under.
The Copyfree Initiative defines Copyfree as a type of permissive copyright license which falls under their Copyfree Standard Definition. which implies distinct licence term requirements analogous to, but different from, those of free software.
Copyfree licenses include the Simplified BSD license, the Open Works license, and others, but not the GNU GPL or other copyleft licenses. The Creative Commons CC0 public domain dedication is also considered to be copyfree.
While all copyfree licenses are permissive licenses, not all permissive licenses are copyfree, since they may introduce limitations not allowed under the copyfree definition. The Apache License 2.0 (as well as previous versions of this license) is an example of a non-copyfree permissive license. Another notable example is the Creative Commons Attribution 3.0 license, which is also incompliant with the Copyfree Standard Definition because the licence forbids DRM technologies.
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, permissive licenses are not actually equivalent to releasing a work into the public domain.
Permissive licenses 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
Permissive licenses make no guarantee that future generations of the software will remain free. This is in contrast to licences which have reciprocity / share-alike requirements. Copyleft is a sharealike license type, "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 licenses, sharealike licensing places more requirement in terms of distribution and combination with software under other licences. Specifically copyleft prohibits freedom to change the license and freedom to strip the granted freedoms.
A major difference between both sets of free software licenses is that when the software is being redistributed (either modified or unmodified), permissive licences don't enforce the redistributor to open the modified source code, while sharealike licenses enforce the publication of the source code under the copyleft license. Some people argue that copyleft licenses see the world as "evil" and therefore enforce "freedoms" ("availability of source code") while permissive license see the world as "good", therefore just allowing good actions and hoping for giving back in form of source code. On the other hand Permissive licenses have often an excellent license compatibility, in comparison to copyleft licenses who sometimes can't be mixed and therefore can't not be always freely combined. However, most software released under GPLv2 allows you to use the terms of later versions of the GPL as well but some have exception clauses that allow combining them with software that is under different licenses or license versions.
But, some older now seldom used permissive free software licenses contain clauses that make them incompatible with copyleft licences. One example is clauses requiring advertising materials to credit the copyright holder. Licenses with this type of advertising clause include the 4-clause BSD license, the PHP License, and the OpenSSL Licence. Popular modern permissive licenses, as the MIT License, the 3-clause BSD license, and the Zlib License, don't include advertising clauses.
Some licenses do not allow derived works to add a restriction that says a redistributor cannot add more restrictions. Examples include the CDDL and MsPL. However such restrictions also make the licence incompatible with permissive free software licences.
While always an important part of the FOSS license landscape, in the 2010s years several authors noted a raising popularity of the permissive licenses in contrast to the copyleft license.
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- "Top 20 licenses". Black Duck Software. 19 November 2015. Retrieved 19 November 2015.
1. MIT license 24%, 2. GNU General Public License (GPL) 2.0 23%, 3. Apache License 16%, 4. GNU General Public License (GPL) 3.0 9%, 5. BSD License 2.0 (3-clause, New or Revised) License 6%, 6. GNU Lesser General Public License (LGPL) 2.1 5%, 7. Artistic License (Perl) 4%, 8. GNU Lesser General Public License (LGPL) 3.0 2%, 9. Microsoft Public License 2%, 10. Eclipse Public License (EPL) 2%
- Balter, Ben (2015-03-09). "Open source license usage on GitHub.com". github.com. Retrieved 2015-11-21.
"1 MIT 44.69%, 2 Other 15.68%, 3 GPLv2 12.96%, 4 Apache 11.19%, 5 GPLv3 8.88%, 6 BSD 3-clause 4.53%, 7 Unlicense 1.87%, 8 BSD 2-clause 1.70%, 9 LGPLv3 1.30%, 10 AGPLv3 1.05%
- permissive on opensource.org "a non-copyleft open source license"
- Choosing an open source license doesn’t need to be scary on choosealicense.com "Which of the following best describes your situation? - I want it simple and permissive."
- The Jargon File contributors (2006). "copycenter". The Jargon File. Eric S. Raymond. Retrieved June 14, 2006.
- "Copyfree Standard Definition". Copyfree Initiative.
- Anonymous. Copyfree Licenses. Copyfree. . URL:http://copyfree.org/licenses/. Accessed: 2013-04-29. (Archived by WebCite® at http://www.webcitation.org/6GFsj0kGe)
- "Copyfree: standard > rejected". Copyfree Initiative. Retrieved 2014-10-26.
Section 4, subsections 2 and 4 of the Apache License 2.0 violate point 3. Free Modification and Derivation of the Copyfree Standard Definition by specifying conditions (beyond licensing) that must apply to modifications.
- US Copyright Office Form CO; see also Ashton-Tate v. Fox
- "Categories of free and nonfree software".
- "What is Copyleft". GNU. Retrieved 21 April 2011.
- Tavares, Gregg (2005-06-01). "Time for the GPL to die". Retrieved 2015-11-27.
- "Licence Compatibility and Interoperability". Open-Source Software - Develop, share, and reuse open source software for public administrations. joinup.ec.europa.eu. Retrieved 2015-05-30.
The licences for distributing free or open source software (FOSS) are divided in two families: permissive and copyleft. Permissive licences (BSD, MIT, X11, Apache, Zope) are generally compatible and interoperable with most other licences, tolerating to merge, combine or improve the covered code and to re-distribute it under many licences (including non-free or “proprietary”).
- Hanwell, Marcus D. (28 Jan 2014). "Should I use a permissive license? Copyleft? Or something in the middle?". opensource.com. Retrieved 2015-05-30.
Permissive licensing simplifies things One reason the business world, and more and more developers [...], favor permissive licenses is in the simplicity of reuse. The license usually only pertains to the source code that is licensed and makes no attempt to infer any conditions upon any other component, and because of this there is no need to define what constitutes a derived work. I have also never seen a license compatibility chart for permissive licenses; it seems that they are all compatible.
- "Frequently Asked Questions about the GNU Licenses – Is GPLv3 compatible with GPLv2?". gnu.org. Retrieved 2014-06-03.
No. Some of the requirements in GPLv3, such as the requirement to provide Installation Information, do not exist in GPLv2. As a result, the licenses are not compatible: if you tried to combine code released under both these licenses, you would violate section 6 of GPLv2. However, if code is released under GPL “version 2 or later,” that is compatible with GPLv3 because GPLv3 is one of the options it permits.
- Landley, Rob. "CELF 2013 Toybox talk - http://landley.net/talks/celf-2013.txt". landley.net. Retrieved 2013-08-21.
GPLv3 broke "the" GPL into incompatible forks that can't share code.
- "GPL-Compatible Free Software Licenses". 2014-11-20. Retrieved 2014-12-29.
- The fall of GPL and the rise of permissive open-source licenses - The GPL is still the world's most popular open-source license but it's declining in use, while permissive licenses are gaining more fans, and some developers are choosing to release code without any license at all. by Steven J. Vaughan-Nichols
- Ronacher, Armin (2013-07-23). "Licensing in a Post Copyright World". lucumr.pocoo.org. Retrieved 2015-11-18.
- The trend towards permissive licensing June 6th, 2011 by Matthew Aslett
- Does your code need a license? Posted 02 May 2013 by Jason Hibbets "Q: Are there software development companies favoring a certain open source license over another? What is the trend in the community? A: We're definitely seeing some trends away from copyleft licenses—mostly towards permissive licenses"