MIT License

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MIT License
Author Massachusetts Institute of Technology
Publisher Massachusetts Institute of Technology
Published 1988[citation needed]
DFSG compatible Yes
FSF approved Yes
OSI approved Yes
GPL compatible Yes
Copyleft No
Linking from code with a different license Yes

The MIT License is a free software license originating at the Massachusetts Institute of Technology (MIT).[1] It is a permissive free software license, meaning that it puts only very limited restriction on reuse and has therefore an excellent license compatibility.[2][3] The MIT license permits reuse within proprietary software provided all copies of the licensed software include a copy of the MIT License terms and the copyright notice. The MIT license is also compatible with many copyleft licenses, such as the GPL; MIT licensed software can be integrated into GPL software, but not the other way around.[4]

While the MIT license was always an important and often used license in the FOSS domain, in 2015 according to Black Duck Software[5] and GitHub data,[6] it became the most popular license ahead of GPL variants and other FOSS licenses.

Notable software packages that use one of the versions of the MIT License include Expat, the Mono development platform class libraries, Ruby on Rails, Node.js, jQuery and the X Window System, for which the license was written.

Various versions[edit]

Because MIT has used many licenses for software, the Free Software Foundation considers "MIT License" ambiguous. "MIT License" may refer to the "Expat License" (used for Expat)[7] or to the "X11 License" (also called "MIT/X Consortium License"; used for the X Window System by the MIT X Consortium).[8] The "MIT License" published by the Open Source Initiative[9] is the same as the "Expat License".

Differing from the Expat License,[7] the X11 License[8] and the "MIT License" chosen for ncurses by the Free Software Foundation[10] include the clause:

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.

License terms[edit]

A common form of the MIT License (from the OSI's website, which is the same version as the "Expat License", and which is not identical to the X source code) is defined as follows:[9]

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:[11]

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.

Comparison to other licenses[edit]

While the MIT as permissive license puts only very limited restrictions and requirements on reuse of code and software, it is not without restriction like public domain.

The MIT License is similar to the 3-clause "modified" BSD license, except that the BSD license contains a notice prohibiting the use of the name of the copyright holder in promotion. This is sometimes present in versions of the MIT License, as noted above.

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[12]) is present in the modified MIT License used by XFree86.

The MIT License states more explicitly the rights given to the end-user, including the right to use, copy, modify, merge, publish, distribute, sublicense, and/or sell the software. The MIT license specifically grants the right to "sublicense" in the text of the license itself — a right not mentioned in the BSD license which simply grants the right to "redistribute and use." The right to sublicense means that the party that receives code under the MIT license grant has the legal right to grant all license rights it received downstream to a third party to whom that licensee distributes the MIT code.[13][better source needed]

Like the BSD license the MIT license does not include an express patent license. Both the BSD and the MIT licenses were drafted before the patentability of software was generally recognized under US law.[14] A similarly permissive license, which includes an explicit contributor's patent license, is the Apache license version 2.0+.

The MIT license contains terms that are used in defining the rights of a patent holder in 35 U.S Code section 154 namely "use," and "sell." This has been construed by some commentators[15] 35 U.S. Code section 154 defines the right of a patent holder as follow: "Every patent shall contain a short title of the invention and a grant to the patentee, his heirs or assigns, of the right to exclude others from making, using, offering for sale, or selling the invention throughout the United States or importing the invention into the United States..."[16] The nature of the right conferred by a U.S. patent is not obvious at first, because it is a negative right, the key is in the words "right to exclude."[17]

The Simplified BSD license used by FreeBSD is essentially identical[citation needed][discuss] to the MIT License, as it contains neither an advertising clause, nor a prohibition on promotional use of the copyright holder's name.

Also similar in terms is the ISC license, which has simpler language.

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.

Reception and impact[edit]

As of 2015 according to Black Duck Software[5] and GitHub,[6] the MIT license was the most popular free software license, with the GNU GPLv2 coming second.

Notable software packages that use one of the versions of the MIT License include Expat, the Mono development platform class libraries, Ruby on Rails, Node.js, Lua (from version 5.0 onwards), jQuery and the X Window System, for which the license was written.

See also[edit]

Portal icon Free software portal

References[edit]

  1. ^ Lawrence Rosen, OPEN SOURCE LICENSING, p.85 (Prentice Hall PTR, 1st ed. 2004)
  2. ^ 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. 
  3. ^ "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”). 
  4. ^ "Various Licenses and Comments about Them". Free Software Foundation. Retrieved 17 July 2013. 
  5. ^ 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% 
  6. ^ a b 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% 
  7. ^ a b "Various Licenses and Comments about Them#Expat License". Free Software Foundation. Retrieved 5 December 2010. 
  8. ^ a b "Various Licenses and Comments about Them#X11 License". Free Software Foundation. Retrieved 5 December 2010. 
  9. ^ a b "Open Source Initiative OSI – The MIT License:Licensing". Open Source Initiative. Retrieved 5 December 2010. 
  10. ^ Dickey, Thomas E. "NCURSES — Frequently Asked Questions (FAQ)". 
  11. ^ "3.3. X Consortium", 3. X/MIT Licenses, The XFree86 Project, March 2004 
  12. ^ "To All Licensees, Distributors of Any Version of BSD". University of California, Berkeley. 1999-07-22. Retrieved 2006-11-15. 
  13. ^ Dictionary.com defines "sublicense" as "a license or contract granted to a third party by a licensee for specified rights or uses of a product, brand name, logo, etc." http://dictionary.reference.com/browse/sublicense
  14. ^ Stern and Allen, Open Source Licensing, p. 495 in Understanding the Intellectual Property License 2013 (Practicing Law Institute 2013)
  15. ^ 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) available at http://www.scribd.com/doc/46088081/Closing-the-Loophole-Open-Source-Licensing-and-the-Implied-Patent-License-Nadan 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.
  16. ^ 35 U.S. Code section 154 at http://www.law.cornell.edu/uscode/text/35/154; Stern and Allen, supra, p. 495
  17. ^ Bitlaw, 1996-2013 Daniel A. Tysver (Beck & Tysver) http://www.bitlaw.com/patent/rights.html

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