Permissive software licence

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Software licenses in context of copyright: permissive licenses second from left as "non-protective FOSS licenses" (adapted from Mark Webbink).[1]

A permissive software license, sometimes also called BSD-like or BSD-style license,[2] is a free software license with minimal requirements about how the software can be redistributed. Examples include the MIT License, BSD licenses, Apple Public Source License and the Apache license. As of 2016, the most popular free software license is the permissive MIT license.[3][4]


The Open Source Initiative defines a permissive software license as a "non-copyleft license".[5] 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."[6] California Western School of Law's defined them as follows: "The ‘BSD-like’ licenses such as the BSD, MIT, and Apache licenses are extremely permissive, requiring little more than attributing the original portions of the licensed code to the original developers in your own code and/or documentation."[2]

Other terms[edit]


Copycenter is a term originally used to explain the modified BSD licence, a permissive free software license. The term was presented by computer scientist and Berkeley Software Distribution (BSD) contributor Marshall Kirk McKusick at a BSD conference in 1999.[citation needed] It is a word play on copyright, copyleft and copy center.

The liberty to 'make as many copies as you want' is in fact also provided by all copyleft licenses. However, unlike both copyleft licenses and copyright law, permissive free software licenses do not control the license terms that a derivative work falls under.

Comparison to public domain[edit]

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,[7] and attribution may still be considered an ethical requirement in academia.

Comparison to copyleft[edit]

A major difference between the set of permissive and copyleft free software licenses is that when the software is being redistributed (either modified or unmodified), permissive licenses do not force the redistributor to open the modified source code. Copyleft licenses enforce the publication of the source code under the copyleft license.[8][9] Some people argue that copyleft licenses see the world as "evil" and therefore enforce "freedoms" such as the availability of source code, while permissive licenses see the world as "good", therefore just allowing good actions and hoping for giving back in form of source code.[10] Permissive licenses do not try to guarantee that future generations of the software will remain free and publicly available, in contrast to licenses which have reciprocity requirements which try to enforce this.

The FreeBSD project argues on the advantages of permissive licenses for companies and commercial use-cases: they say that they place only "minimal restrictions on future behavior" and argue that copyleft licenses are "legal time-bombs".[11]

Permissive licenses offer more extensive licence compatibility than copyleft licenses, which cannot always be freely combined and mixed.[12][13][14][15]

License compatibility[edit]

License compatibility between common free and open-source software (FOSS) licenses according to David A. Wheeler (2007): the vector arrows denote a one directional compatibility, therefore better compatibility on the left side ("permissive licenses") than on the right side ("copyleft licences").[16]

In general permissive licenses show a good licence compatibility with most other software licenses in most situations.[12][13]

Due to their non-restrictiveness most permissive software licenses are even compatible with copyleft licenses, which are incompatible with most other licenses. Copyleft licenses don't allow the addition of additional restrictive clauses which would be often required in a combined work made from copyleft code and other licensed code. Only some older permissive licenses have clauses requiring advertising materials to credit the copyright holder which made them incompatible with copyleft licenses, for instance the 4-clause BSD license, the PHP Licence, and the OpenSSL License. Popular modern permissive licenses, as the MIT Licence, the 3-clause BSD licence, and the Zlib Licence, don't include advertising clauses and are compatible with many copyleft licenses.

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 license incompatible with permissive free software licenses.

Some licenses are permissive but do not qualify as free software licenses as defined by the Free Software Foundation.

Reception and adoption[edit]

While always an important part of the free and open-source software (FOSS) license landscape, since around 2010, several authors noted a raising popularity of the permissive licenses in contrast to the copyleft license.[17][18][19][20]

As of 2015, the MIT licence, a permissive license, is the most popular license in the FOSS domain before a copyleft one, the second placed GPLv2.[3][4]

See also[edit]


  1. ^ Open Source from a Proprietary Perspective at the Wayback Machine (archive index)
  2. ^ a b New Media Rights (2008-09-12). "Open Source Licensing Guide". California Western School of Law.
  3. ^ a b "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%
  4. ^ a b Balter, Ben (2015-03-09). "Open source license usage on". 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%
  5. ^ permissive on "A "permissive" license is simply a non-copyleft open source license – one that guarantees the freedoms to use, modify, and redistribute, but that permits proprietary derivatives."
  6. ^ Choosing an open source license doesn’t need to be scary on "Which of the following best describes your situation? – I want it simple and permissive."
  7. ^ US Copyright Office Form CO; see also Ashton-Tate v. Fox
  8. ^ "What is Copyleft". GNU. Retrieved 21 April 2011.
  9. ^ "Categories of free and nonfree software".
  10. ^ Tavares, Gregg (2005-06-01). "Time for the GPL to die". Retrieved 2015-11-27. '
  11. ^ Montague, Bruce (2013-11-13). "Why you should use a BSD style license for your Open Source Project". FreeBSD. Retrieved 2015-11-28. 9. GPL Advantages and Disadvantages [..] 12. Conclusion
    In contrast to the GPL, which is designed to prevent the proprietary commercialization of Open Source code, the BSD license places minimal restrictions on future behavior. This allows BSD code to remain Open Source or become integrated into commercial solutions, as a project's or company's needs change. In other words, the BSD license does not become a legal time-bomb at any point in the development process.

    In addition, since the BSD license does not come with the legal complexity of the GPL or LGPL licenses, it allows developers and companies to spend their time creating and promoting good code rather than worrying if that code violates licensing.
  12. ^ a b "Licence Compatibility". European Union Public Licence. Archived from the original on 2015-06-17. Retrieved 2015-05-30. The licenses for distributing free or open source software (FOSS) are divided in two families: permissive and copyleft. Permissive licenses (BSD, MIT, X11, Apache, Zope) are generally compatible and interoperable with most other licenses, tolerating to merge, combine or improve the covered code and to re-distribute it under many licenses (including non-free or “proprietary”).
  13. ^ a b Hanwell, Marcus D. (2014-01-28). "Should I use a permissive license? Copyleft? Or something in the middle?". 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.
  14. ^ "Frequently Asked Questions about the GNU Licenses – Is GPLv3 compatible with GPLv2?". 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.
  15. ^ Landley, Rob. "CELF 2013 Toybox talk". Retrieved 2013-08-21. GPLv3 broke "the" GPL into incompatible forks that can't share code.
  16. ^ The Free-Libre / Open Source Software (FLOSS) License Slide by David A. Wheeler on September 27, 2007
  17. ^ Vaughan-Nichols, Steven J. "The fall of GPL and the rise of permissive open-source licenses". Retrieved 2015-11-28. 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.
  18. ^ Ronacher, Armin (2013-07-23). "Licensing in a Post Copyright World". Retrieved 2015-11-18.
  19. ^ Aslett, Matthew (2011-06-06). "The trend towards permissive licensing". Retrieved 2015-11-28.
  20. ^ 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"

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