Permissive software license

A permissive software license, sometimes also called BSD-like or BSD-style license,[1] is a free-software license with minimal requirements about how the software can be redistributed. Examples include the GNU All-permissive License, MIT License, BSD licenses, Apple Public Source License and Apache license. As of 2016, the most popular free-software license is the permissive MIT license.[2][3] Permissive licenses do not try to guarantee that future versions of the software will remain free and publicly available, in contrast to copyleft licenses, which have reciprocity requirements which try to enforce this.[4] Software under a permissive license can later be made proprietary.[5]

Public domain & equivalentsPermissive licenseCopyleft (protective license)Noncommercial licenseProprietary licenseTrade secret
Description Grants all rightsGrants use rights, including right to relicense (allows proprietization, license compatibility)Grants use rights, forbids proprietizationGrants rights for noncommercial use only. May be combined with copyleft.Traditional use of copyright; no rights need be grantedNo information made public
Software PD, CC0MIT, Apache, MPLGPL, AGPLJRL, AFPLproprietary software, no public licenseprivate, internal software
Other creative works PD, CC0CC-BYCC-BY-SACC-BY-NCCopyright, no public licenseunpublished

Example

The following is the full text of the simple GNU All-permissive License:

Copyright <YEAR>, <AUTHORS>

Copying and distribution of this file, with or without modification, are permitted in any medium without royalty, provided the copyright notice and this notice are preserved. This file is offered as-is, without any warranty.

— GNU All-permissive License[6][7]

Definitions

The Open Source Initiative defines a permissive software license as a "non-copyleft license".[8] 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."[9] California Western School of Law's newmediarights.com 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."[1]

Comparison to copyleft

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.[10][11] 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.

Defining how much liberal a license is, however, is not something easily quantifiable, and often depends on the goals of the final users. If the latter are developers, for some it might be valuable to have the right to modify and exploit source code written by others and possibly incorporate it into proprietary code and make money with it (and therefore these see permissive licenses as offering them a "right"),[12] while for other developers it might be more valuable to know that nobody will ever capitalize what has mostly been their work (and therefore these see copyleft licenses as offering them a "right"). Furthermore, the final users might not be developers at all, and in this case copyleft licenses offer them the everlasting right to access a software as free software, ensuring that it will never become closed source – while permissive licenses offer no rights at all to non-developer final users, and software released with a permissive license could theoretically become from one day to another a closed source malware without the user even knowing it.

Permissive licenses offer more extensive licence compatibility than copyleft licenses, which cannot always be freely combined and mixed.[13][14][15][16]

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

License compatibility
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").[18]

In general permissive licenses show a good licence compatibility with most other software licenses in most situations.[13][14]

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 License 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

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.[19][20][21][22]

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.[2][3]

Other terms

Copycenter

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. 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, but with the requirement that the source code also be made available. Copyleft says that anyone who redistributes the software, with or without changes, must pass along the freedom to further copy and change it.[23] However, unlike both copyleft licenses and copyright law, permissive free-software licenses do not control the license terms that a derivative work falls under.

Pushover license

In the Free Software Foundation's guide to license compatibility and relicensing, Richard Stallman defines permissive licenses as "pushover licenses", comparing them to those people who "can't say no", because among the things these licenses permit there is also the right to deny freedom to others.[24] The Foundation recommends pushover licenses only for small programs, below 300 lines of code, where "the benefits provided by copyleft are usually too small to justify the inconvenience of making sure a copy of the license always accompanies the software".[25]

See also
  • List of permissive software licenses
  • License-free software
  • Public domain equivalent license
  • Free-software license
  • Comparison of free and open-source software licenses
  • Free Software Foundation

References
  1. New Media Rights (2008-09-12). "Open Source Licensing Guide". California Western School of Law.
  2. "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%
  3. 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%
  4. "gnu.org". www.gnu.org.
  5. Amadeo, Ron (21 July 2018). "Google's iron grip on Android: Controlling open source by any means necessary". Ars Technica.
  6. Free Software Foundation, Various Licenses and Comments about Them, GNU All-permissive License
  7. Information for Maintainers of GNU Software, License Notices for Other Files
  8. permissive on opensource.org "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."
  9. 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."
  10. "What is Copyleft". GNU. Retrieved 21 April 2011.
  11. "Categories of free and nonfree software". gnu.org.
  12. With this in mind, the FreeBSD project advocates 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". See 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.
  13. "Licence Compatibility". European Union Public Licence. joinup.ec.europa.eu. 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”).
  14. Hanwell, Marcus D. (2014-01-28). "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.
  15. "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.
  16. Landley, Rob. "CELF 2013 Toybox talk". landley.net. Retrieved 2013-08-21. GPLv3 broke "the" GPL into incompatible forks that can't share code.
  17. US Copyright Office Form CO; see also Ashton-Tate v. Fox
  18. The Free-Libre / Open Source Software (FLOSS) License Slide by David A. Wheeler on September 27, 2007
  19. Vaughan-Nichols, Steven J. "The fall of GPL and the rise of permissive open-source licenses". zdnet.com. 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.
  20. Ronacher, Armin (2013-07-23). "Licensing in a Post Copyright World". lucumr.pocoo.org. Retrieved 2015-11-18.
  21. Aslett, Matthew (2011-06-06). "The trend towards permissive licensing". the451group.com. Retrieved 2015-11-28.
  22. 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"
  23. url=https://www.gnu.org/licenses/copyleft.en.html
  24. Stallman, Richard (2016-02-08). "License Compatibility and Relicensing". Free Software Foundation. Retrieved 2019-09-29. In general, lax permissive licenses (modified BSD, X11, Expat, Apache, Python, etc.) are compatible with each other. That's because they have no requirements about other code that is added to the program. They even permit putting the entire program (perhaps with changes) into a proprietary software product; thus, we call them "pushover licenses" because they can't say "no" when one user tries to deny freedom to others.
  25. How to choose a license for your own work – Free Software Foundation
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