MIT License

From Wikipedia, the free encyclopedia

Jump to navigationJump to search

MIT License

Publisher	Massachusetts Institute of Technology
SPDX identifier	MIT
Debian FSG compatible	Yes
FSF approved	Yes
OSI approved	Yes
GPL compatible	Yes
Copyleft	No
Linking from code with a different licence	Yes

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]

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), Google (Angular) 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.

Minor ambiguity and variants

In common usage there is only one MIT licence, as illustrated by Github's licensing advice and the legal text for MIT at Github's service choosealicence.com.

More precisely, the MIT has been using many licenses for software since its creation, so the phrase "the MIT License" is theoretically ambiguous.^[15] For example, the MIT offers four licensing options for the FFTW^[16] C source code library, one of which is the GPLv 2.0 and the other three of which are not open-source.

"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 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 X Consortium was dissolved late in 1996, and its assets transferred to The Open Group,^[19] which released X11R6 initially under the same license. The X11 License^[18] and the X11R6 "MIT License" chosen for ncurses by the Free Software Foundation^[20] 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.

As of 2020, the successor to the X Window System is the X.Org Server, which is licensed under what is effectively the common MIT licence, according to the X.org licensing page:

The X.Org Foundation has chosen the following format of the MIT License as the preferred format for code included in the X Window System distribution. This is a slight variant of the common MIT license form published by the Open Source Initiative

The "slight variant" is the addition of the phrase "(including the next paragraph)".

Comparison to other licenses

BSD

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^[21]) 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.^[22][23]

GNU GPL

The GNU GPL is explicit about the patent grant an author would be giving when the code(or derivative work) is distributed,^[24] the MIT license does not discuss patents. Moreover, the GPL license impacts "derivative works", but the MIT license does not.

Relation to patents

Like the BSD license, the MIT license does not include an express patent license although some commentators^[25][26] 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.^[27] The Apache License version 2.0^[2] is a similarly permissive license that includes an explicit contributor's patent license. Of specific relevance to US jurisdictions, the MIT license uses the terms "sell" and "use" that are also used in defining the rights of a patent holder in Title 35 of the United States Code section 154. This has been construed by some commentators^[28][29] as an unconventional but implicit license in the US to use any underlying patents.

Origins

One of the originators of the MIT license, computer scientist Jerry Saltzer, has published his recollections of its early development, along with documentary evidence.^[30] See also.^[6]

Reception

As of 2020, according to WhiteSource Software^[11] the MIT license was used in 27% of four million open source packages. As of 2015, according to Black Duck Software^{[31][better source needed]} 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.

This article uses material from the Wikipedia article  Metasyntactic variable, which is released under the  Creative Commons Attribution-ShareAlike 3.0 Unported License.