MIT License

The MIT License is a permissive free software license originating at the Massachusetts Institute of Technology (MIT)[5] in the late 1980s.[6] As a permissive license, it puts only very limited restriction on reuse and has, therefore, high license compatibility.[7][8]

MIT License
PublisherMassachusetts Institute of Technology
SPDX identifierMIT
DFSG compatibleYes[1]
FSF approvedYes[2][3]
OSI approvedYes[4]
GPL compatibleYes[2][3]
CopyleftNo[2][3]
Linking from code with a different licenceYes

It is compatible because it can be re-licensed under other licenses. The MIT license is compatible with many copyleft licenses, such as the GNU General Public License (GPL); MIT licensed software can be re-licensed as GPL software, and integrated with other GPL software, but not the other way around.[9] The MIT license also permits reuse within proprietary software, provided that either all copies of the licensed software include a copy of the MIT License terms and the copyright notice, or the software is re-licensed to remove this requirement. MIT-licensed software can also be re-licensed as proprietary software,[10][8] which distinguishes it from copyleft software licenses. As of 2020, MIT was the most popular software license found in one analysis[11], continuing from reports in 2015 that MIT was the most popular software license on GitHub, ahead of any GPL variant and other free and open-source software (FOSS) licenses.[12]

Notable projects that use the MIT License include the X Window System, Ruby on Rails, Node.js, Lua and jQuery. Notable companies using the MIT license include Microsoft (.NET Core) and Facebook (React).

License terms

A common form of the MIT License is this (taken from the Open Source Initiative's website; this is identical to the "Expat License", and different from the license used in the X source code):[13]

Copyright (c) <year> <copyright holders>

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

An intermediate form of license used by the X Consortium for X11 used the following wording:[14]

Copyright (C) <date> X Consortium

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE X CONSORTIUM BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Except as contained in this notice, the name of the X Consortium shall not be used in advertising or otherwise to promote the sale, use or other dealings in this Software without prior written authorization from the X Consortium.

X Window System is a trademark of X Consortium, Inc.

Ambiguity and variants

Because the MIT has been using many licenses for software since its creation, saying "the MIT License" is ambiguous[15]. For example, the MIT offers several licensing options for FFTW[16].

"MIT License" may refer to the Expat License (used for the XML parsing library Expat)[17] or to the X11 License (also called "MIT/X Consortium License"; used for the X Window System by the MIT X Consortium).[18] The "MIT License" published by the Open Source Initiative[13] is the same as the "Expat License".

The X11 License[18] and the "MIT License" chosen for ncurses by the Free Software Foundation[19] both include the following clause, absent in the Expat License:[17]

Except as contained in this notice, the name(s) of the above copyright holders shall not be used in advertising or otherwise to promote the sale, use or other dealings in this Software without prior written authorization.

Comparison to other licenses

The original BSD license also includes a clause requiring all advertising of the software to display a notice crediting its authors. This "advertising clause" (since disavowed by UC Berkeley[20]) is present in the modified MIT License used by XFree86.

The University of Illinois/NCSA Open Source License combines text from both the MIT and BSD licenses; the license grant and disclaimer are taken from the MIT License.

The ISC license contains similarities to both the MIT and simplified BSD licenses, the biggest difference being that language deemed unnecessary by the Berne Convention is omitted.[21][22]

Relation to patents

Like the BSD license, the MIT license does not include an express patent license although some commentators[23][24] state that the grant of rights covers all potential restrictions including patents. Both the BSD and the MIT licenses were drafted before the patentability of software was generally recognized under US law.[25] The Apache License version 2.0[2] is a similarly permissive license that includes an explicit contributor's patent license. In the US, the MIT license contains the terms "use" and "sell" that are used in defining the rights of a patent holder in 35 U.S. Code section 154. This has been construed by some commentators[26][27] as an unconventional but implicit license in the US to use any underlying patents.

Reception

As of 2020, according to White Sources Software[11] the MIT license was used in 27% of four million open source packages. As of 2015, according to Black Duck Software[28] and a 2015 blog[12] from GitHub, the MIT license was the most popular free software license, with the GNU GPLv2 coming second in their sample of repositories. In June 2016, an analysis of the Fedora Project's packages revealed the MIT as most used license.[29]

gollark: You've gone from "cheap bit of rock" to "needs some sort of integrated circuit, propellant reservoir and engine".
gollark: It would be very expensive to give each individual pellet some sort of onboard computer.
gollark: Or things which exploit flaws in the checking process.
gollark: Might it not also select for weirdly low probability system failures?
gollark: There's that xkcd what-if about moving the moon with giant lasers... you might be able to do that, too.

See also
  • Comparison of free and open-source software licenses
  • ISC license – similar to the MIT license, but with language deemed unnecessary removed
  • Category:Software using the MIT license

References
  1. "License information". The Debian Project. Software in the Public Interest (published 2017-07-12). 1997–2017. Archived from the original on 2017-07-20. Retrieved 2017-07-20. ... This page presents the opinion of some debian-legal contributors on how certain licenses follow the Debian Free Software Guidelines (DFSG). ... Licenses currently found in Debian main include:
    • ...
    • Expat/MIT-style licenses
    • ...
  2. "Various Licenses and Comments about Them". The GNU Project. Free Software Foundation (published 2017-04-04). 2014–2017. Expat License. Archived from the original on 2017-07-20. Retrieved 2017-07-20. ... This is a lax, permissive non-copyleft free software license, compatible with the GNU GPL. It is sometimes ambiguously referred to as the MIT License. ...
  3. "Various Licenses and Comments about Them". The GNU Project. Free Software Foundation (published 2017-04-04). 2014–2017. X11 License. Archived from the original on 2017-07-20. Retrieved 2017-07-20. ... This is a lax permissive non-copyleft free software license, compatible with the GNU GPL. ... This license is sometimes called the MIT license, but that term is misleading, since MIT has used many licenses for software. ...
  4. "Licenses by Name". Open Source Initiative. n.d. Archived from the original on 2017-07-20. Retrieved 2017-07-20. ... The following licenses have been approved by the OSI. ...
    • ...
    • MIT License (MIT)
    • ...
  5. Lawrence Rosen, OPEN SOURCE LICENSING, p.85 (Prentice Hall PTR, 1st ed. 2004)
  6. "The mysterious history of the MIT License". opensource.com. opensource.com. Retrieved 2019-07-30. The date? The best single answer is probably 1987. But the complete story is more complicated and even a little mysterious. [...] Precursors from 1985. The X Consortium or X11 License variant from 1987. Or the Expat License from 1998 or 1999.
  7. 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.
  8. "Licence Compatibility and Interoperability". Open-Source Software - Develop, share, and reuse open source software for public administrations. joinup.ec.europa.eu. Archived from the original on 2015-06-17. 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').
  9. "Various Licenses and Comments about Them". Free Software Foundation. Retrieved 17 July 2013.
  10. https://softwareengineering.stackexchange.com/questions/264700/paid-software-includes-mit-licensed-library-does-that-put-my-app-under-mit-too
  11. "Open Source Licenses in 2020: Trends and Predictions". 2020-05-03. Archived from the original on 2020-05-03. Retrieved 2020-05-03.
  12. 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%
  13. "Open Source Initiative OSI – The MIT License:Licensing". Open Source Initiative. Retrieved 5 December 2010.
  14. "3.3. X Consortium", 3. X/MIT Licenses, The XFree86 Project, March 2004
  15. "Various Licenses and Comments about Them". GNU Project. Retrieved 17 July 2020.
  16. "FFTW - Fastest Fourier Transform in the West". Massachusetts Institute of Technology. Retrieved 17 July 2020.
  17. "Various Licenses and Comments about Them#Expat License". Free Software Foundation. Retrieved 5 December 2010.
  18. "Various Licenses and Comments about Them#X11 License". Free Software Foundation. Retrieved 5 December 2010.
  19. Dickey, Thomas E. "NCURSES — Frequently Asked Questions (FAQ)".
  20. "To All Licensees, Distributors of Any Version of BSD". University of California, Berkeley. 1999-07-22. Retrieved 2006-11-15.
  21. "Copyright Policy". OpenBSD. Retrieved 6 June 2016. The ISC copyright is functionally equivalent to a two-term BSD copyright with language removed that is made unnecessary by the Berne convention.
  22. de Raadt, Theo (21 March 2008). "Re: BSD Documentation License?". openbsd-misc (Mailing list).
  23. "Why so little love for the patent grant in the MIT License?". 2020-05-03. Archived from the original on 2020-05-03. Retrieved 2020-05-03.
  24. "Free and open source software and your patents". 2020-05-03. Archived from the original on 2020-05-03. Retrieved 2020-05-03.
  25. Stern and Allen, Open Source Licensing, p. 495 in Understanding the Intellectual Property License 2013 (Practicing Law Institute 2013)
  26. "The MIT License, Line by Line". 2020-05-03. Archived from the original on 2020-05-03. Retrieved 2020-05-03.
  27. Christian H. Nadan, Closing the Loophole; Open Source Licensing and the Implied Patent License, THE COMPUTER AND INTERNET LAWYER, Vol. 26, No. 8 (Aug. 2009) who argues that "By using patent terms like "deal in", "use", and "sell", the MIT license grant is more likely to be deemed to include express patent rights than the BSD license."
  28. "Top 20 licenses". Black Duck Software. 19 November 2015. Archived from the original on 4 September 2013. Retrieved 19 November 2015. 1. MIT license 24%, 2. GNU General Public License (GPL) 2.0 23%
  29. Anwesha Das (22 June 2016). "Software Licenses in Fedora Ecosystem". anweshadas.in. Retrieved 2016-06-27. In the above bar-chart I have counted GPL and its different versions as one family, and I did the same with LGPL too. From this diagram it is very much clear that the MIT License is the most used license, with a total number of use case of 2706.Therefore comes GPL(i.e GNU General Public License) and its different versions, BSD, LGPL (i.e GNU Lesser General Public License) and its different versions, ASL (i.e Apache Software License) family, MPL (i.e Mozilla Public License). Apart from these licenses there are projects who has submitted themselves in to Public Domain and that number is 137.

Further reading
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