Permissive software license

A permissive software license, sometimes also called BSD-like or BSD-style license,[1] is a free-software license with only minimal restrictions on how the software can be used, modified, and redistributed, usually including a warranty disclaimer. 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]

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[4][5]

Definitions

The Open Source Initiative defines a permissive software license as a "non-copyleft license that guarantees the freedoms to use, modify and redistribute".[6] GitHub's choosealicense website describes the permissive MIT license as "[letting] people do anything they want with your code as long as they provide attribution back to you and don’t hold you liable."[7] 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
Further information: Copyleft
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, CC0BSD, MIT, ApacheGPL, AGPLJRL, AFPLproprietary software, no public licenseprivate, internal software
Other creative works PD, CC0CC-BYCC-BY-SACC-BY-NCCopyright, no public licenseunpublished

Copyleft licenses generally require the reciprocal publication of the source code of any modified versions under the original work's copyleft license.[8][9] Permissive licenses, in contrast, do not try to guarantee that modified versions of the software will remain free and publicly available, generally requiring only that the original copyright notice be retained.[1] As a result, derivative works, or future versions, of permissively-licensed software can be released as proprietary software.[10]

Permissive licenses offer more extensive licence compatibility than copyleft licenses, which cannot generally be freely combined and mixed, because their reciprocity requirements conflict with each other.[11][12][13][14][15]

Comparison to public domain
Further information: Public domain software and Public-domain-equivalent license

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

Advocates of permissive licenses often recommend against attempting to release software to the public domain, on the grounds that this can be legally problematic in some jurisdictions.[17][18] Public-domain-equivalent licenses are an attempt to solve this problem, providing a fallback permissive license for cases where renunciation of copyright is not legally possible, and sometimes also including a disclaimer of warranties similar to most permissive licenses.

License compatibility
Main article: 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").[19]

In general permissive licenses have good licence compatibility with most other software licenses in most situations.[11][12]

Due to their non-restrictiveness, most permissive software licenses are even compatible with copyleft licenses, which are incompatible with most other licenses. Some older permissive licenses, such as the 4-clause BSD license, the PHP License, and the OpenSSL License, have clauses requiring advertising materials to credit the copyright holder, which made them incompatible with copyleft licenses. Popular modern permissive licenses, however, such as the MIT Licence, the 3-clause BSD licence and the zlib licence, don't include advertising clauses and are generally compatible with 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.

Reception and adoption

While they have been in use since the mid-1980s[20], several authors noted an increase in the popularity of permissive licenses during the 2010s.[21][22][23][24]

As of 2015, the MIT licence, a permissive license, is the most popular free software license, followed by GPLv2.[2][3]

Other terms

Berkeley had what we called "copycenter," which is "take it down to the copy center and make as many copies as you want."

— Marshall Kirk McKusick, [25]

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.[25][26]

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 they are seen as granting a right to "deny freedom to others."[27] 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".[28]

gollark: Yes, and user code should be able to do the same stuff.
gollark: Apparently.
gollark: Yes, a type which gets operator support.
gollark: So it *does* have operator overloading, but only as builtin magic.
gollark: It's Google, has better memory management, and something something concurrency.

See also

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. Archived from the original on 19 July 2016. 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. Free Software Foundation, Various Licenses and Comments about Them, GNU All-permissive License
  5. Information for Maintainers of GNU Software, License Notices for Other Files
  6. 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."
  7. 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."
  8. "What is Copyleft". GNU. Retrieved 21 April 2011.
  9. "Categories of free and nonfree software". gnu.org.
  10. Amadeo, Ron (21 July 2018). "Google's iron grip on Android: Controlling open source by any means necessary". Ars Technica.
  11. "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”).
  12. 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.
  13. "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.
  14. Landley, Rob. "CELF 2013 Toybox talk". landley.net. Retrieved 2013-08-21. GPLv3 broke "the" GPL into incompatible forks that can't share code.
  15. "Interpreting, enforcing and changing the GNU GPL, as applied to combining Linux and ZFS". fsf.org. Retrieved 2020-06-08.
  16. US Copyright Office Form CO; see also Ashton-Tate v. Fox
  17. "OpenBSD Copyright Policy". The OpenBSD project. Retrieved 2020-06-09. In some jurisdictions, it is doubtful whether voluntarily placing one's own work into the public domain is legally possible. For that reason, to make any substantial body of code free, it is preferable to state the copyright and put it under an ISC or BSD license instead of attempting to release it into the public domain.
  18. Hipp, D. Richard. "Why SQLite succeeded as a database". The Changelog. Also at the time I did not realize, having lived my whole life in the United States, which is, you know, under British common law, where the public domain is something that’s recognized. I did not realize that there were a lot of jurisdictions in the world where it’s difficult or impossible for someone to place their works in the public domain. I didn’t know. So that’s a complication.
  19. The Free-Libre / Open Source Software (FLOSS) License Slide by David A. Wheeler on September 27, 2007
  20. Haff, Gordon. "The mysterious history of the MIT License". opensource.com. Retrieved 2020-06-08. [There's] a good argument to be made that the MIT License, also called the X Consortium or X11 License at the time, crystallized with X11 in 1987, and that's the best date to use. You could argue it was created in 1985 with possible adjustments over the next couple of years.
  21. 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.
  22. Ronacher, Armin (2013-07-23). "Licensing in a Post Copyright World". lucumr.pocoo.org. Retrieved 2015-11-18.
  23. Aslett, Matthew (2011-06-06). "The trend towards permissive licensing". the451group.com. Archived from the original on 2015-10-13. Retrieved 2015-11-28.
  24. 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"
  25. "Add Kirk's comment about "copycenter"; it's just too good to pass up". Historical FreeBSD fortune(6) database. Retrieved 2020-06-08.
  26. Raymond, Eric S. "copycenter". The Jargon File.
  27. 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.
  28. How to choose a license for your own work – Free Software Foundation
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