Open-source license

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Popular open source licenses include the Apache License, the MIT License, the GNU General Public License (GPL), the BSD Licenses, the GNU Lesser General Public License (LGPL) and the Mozilla Public License (MPL).

Open-source licenses facilitate free and open-source software development. Intellectual property laws restrict the modification and sharing of creative works. Open-source licenses use these existing legal structures for the inverse purpose of granting freedoms that facilitate sharing and collaboration. They grant the recipient the rights to use the software, examine the source code, modify it, and distribute the modified software. Open-source licenses target computer software where source code can be necessary to create modifications. They also cover situations where there is no difference between the source code and the executable program distributed to end users. Open-source licenses can cover hardware, infrastructure, drinks, books, art, and music.

There are two broad categories of open-source licenses, permissive and copyleft. Permissive licenses originate in university software development. They grant the recipient the rights to modify and distribute the software with certain conditions. Permissive licenses usually require attribution to credit the original authors and a disclaimer of warranty. Copyleft licenses have their origins in the free software movement. Copyleft licenses also grant the recipient the rights to modify and distribute the software, and require attribution and disclaim warranties. The difference is that copyleft licenses demand reciprocity. Any derivative works must be distributed with source code and under a copyleft license.


Intellectual property (IP) is a legal category that treats works of creativity like physical property. Multiple types of IP cover software including trademarks, patents, and copyrights. Most countries, including the United States (US), have created copyright laws in line with the Berne Convention. These laws automatically assign a copyright whenever a creator releases their work in any fixed format.[1] Under US copyright law, the initial creation of software is called the original work. The creator, or their employer, holds the copyright to this original work. They alone are permitted to make copies, release modified versions, distribute copies, perform publicly, or display the work publicly. Under US copyright law, modified versions of the original work are called derivative works. When a creator modifies an existing work, they only hold the copyright to their modifications. Unless the original work was in the public domain, a derivative work can only be distributed with the permission of all copyright holders. This poses a problem for collaborative development because each update would require the unanimous consent of every contributor.[2]

In 1980, the US government amended the law to treat software as a literary work. All software released after this point was automatically restricted by IP law.[3] At that time, American activist and programmer Richard Stallman was working as a graduate student at the MIT Computer Science and Artificial Intelligence Laboratory. Stallman witnessed the fragmentation that proprietary software caused, and founded the free software movement. Throughout the 1980s, he started the GNU Project to create a free operating system, wrote essays on software freedom, founded the Free Software Foundation, and wrote several free software licenses. Stallman's free software licenses used the existing intellectual property laws to subvert their intended goal of restriction. Free software licenses explicitly provided freedoms to the recipient.[4]

In 1998, Bruce Perens and Eric S. Raymond founded the Open Source Initiative (OSI). Both were active members of the free software community. At Debian, Perens had written the Debian Free Software Guidelines. He used this as the basis for The Open Source Definition. Raymond was a strong proponent of the name "open source" over free software. He viewed open-source as more appealing to businesses and more reflective of the tangible advantages of open-source software development. One of Raymond's goals was to expand the free software community to include large commercial developers.[5] In The Cathedral and the Bazaar, Raymond compared open-source development to the bazaar, an open-air public market. He argued that aside from free software ethics, open-source development provided advantages that proprietary software could not replicate. Raymond focused heavily on feedback, testing, and bug reports. He contrasted the proprietary model where small pools of secretive workers would carry out this work with the open-source development of Linux where the pool of testers included potentially the entire world. He summarized this strength as "Given enough eyeballs, all bugs are shallow."[6] The OSI succeeded in bringing open-source development to corporate software developers including Sun Microsystems, IBM, Netscape, Mozilla, Apache, Apple Inc., Microsoft, and Nokia. These companies both released software under existing open-source licenses and drafted their own licenses to be approved by the OSI.[7]


Open-source software licenses and how they interact

Open-source licenses are categorized as copyleft or permissive. Copyleft licenses require derivative works to include source code under a copyleft license. Permissive licenses do not. Copyleft can be further divided into strong and weak for licenses that define derivative works broadly or narrowly.[8]


Permissive licenses, also known as academic licenses, allow recipients to use, modify, and distribute software with no obligation to provide source code. Institutions created these licenses to distribute software to the public.[9] Permissive licenses are usually short, often less than a page of text. They impose few conditions. Most include disclaimers and obligations to credit authors. A few include explicit provisions for patents, trademarks, and other forms of intellectual property.[10]

The University of California, Berkeley created the first open-source license, the Berkeley Software Distribution (BSD) license to permit free usage with no obligations placed on users. The BSD license brought the concept of academic freedom of ideas to software. Early academic software authors had shared code based on implied promises. Berkley made these concepts explicit with clear disclaimers for liability and warranty and several conditions, or clauses, for redistribution. The Massachusetts Institute of Technology (MIT) created a permissive license based on the BSD license. The MIT license clarified the conditions by making them more explicit. For example, the MIT license describes the right to sublicense. One of the strengths of open-source development is the complex process where developers can build on the derivative works of each other and combine their projects into collective works. Explicitly making the license sublicensable provides a legal advantage when tracking the chain of authorship.[11] The BSD and MIT are template licenses that can be adapted to any software. They are widely adapted and used by many open-source projects. The Apache License is a permissive license more explicit that the MIT License. It offers legal advantages over template licenses and provides similar grants.[12]


Copyleft licenses are reciprocal in nature. They offer the rights to use, modify, and distribute the software on the condition that people must release derivative works under a copyleft license offering these freedoms. Software built on a copyleft base must come with the source code. They offer protection against proprietary software consuming open-source code without giving back. Free software activist and programmer Richard Stallman stated that "the central idea of copyleft is to use copyright law, but flip it over to serve the opposite of its usual purpose: instead of a means of privatizing software, [copyright] becomes a means of keeping software free."[13]

Copyleft started in the Free Software Foundation (FSF) and the broader free software movement. Richard Stallman wrote the first version of the General Public License (GPL) in response to perceived issues in proprietary software. Proprietary software restricts how a person can use their own computer, and it could lead to a fragmented computing landscape. Stallman promotes the copyleft GPL on the ethical basis that it should foster cooperation and improve society.[14]

Practical benefits to copyleft licenses have attracted commercial developers. Corporations have used and written copyleft licenses with a narrower scope than the GPL. The GPL remains the most popular license of this type, but there are other significant examples. The FSF has crafted the Lesser General Public License (LGPL) for libraries. Mozilla uses the Mozilla Public License (MPL) for their releases, including Firefox. IBM drafted the Common Public License (CPL) and later adopted the Eclipse Public License (EPL). A difference between the GPL and other copyleft licenses is how they define derivative works covered by the license. The GPL, and the Affero License based on it, use a broad scope to describe affected works.[15] They are called strong copyleft in contrast to the weaker copyleft licenses often used by corporations. Weak copyleft uses narrower, explicit definitions of derivative works.[16] The MPL uses a file-based definition, the CPL/EPL use a module-based definition, and FSF's own LGPL exempts libraries in certain situations.[7]


Free software[edit]

Nearly all free software licenses are also open-source software licenses. The separate terms free software and open-source software reflect different values rather than a technical or legal difference. The founder of the Free Software Foundation (FSF), Richard Stallman, stated that "free software is an ethical imperative" in contrast to the practical aims of open-source software.[17] The criteria for free and open-source licenses are both similar and related. The Debian project used the "four freedoms" of the Free Software Foundation when creating their own Debian Free Software Guidelines (DSFG) to determine what content was allowed into the Debian operating system. The Open Source Initiative then based The Open Source Definition on the DSFG.[18]

There are occasional edge cases where either the FSF or the OSI accept a license but not both. For example, only the OSI approved the Open Watcom license. The FSF viewed their Sybase Open Watcom Public License as non-free because it required published source code for private modifications. Situations like this are rare. All major free software licenses are open-source, including the GPL.[19]

Public domain[edit]

When a copyright expires, the work enters into the public domain. At that point, no one has exclusive rights, and it is freely available to anyone.[20] According to attorney Lawrence Rosen, copyright laws were not written with the expectation that creators would release their work into the public domain. Thus intellectual property laws lack clear paths to waive a copyright. Highly permissive licenses described as "public domain" may legally function as unilateral contracts that offer something but impose no terms.[21]

Brief, permissive licenses called "public domain" licenses, like the Creative Commons CC0, provide a simple waiver of copyright claims into the public domain. Then because there are no standard methods to waive copyrights, they provide an open-source permissive software license as a fallback. In jurisdictions that do not accept a pubic domain waiver, the permissive license takes effect.[22] Public domain waivers share limitations with simple permissive licenses including limited protection against patent or trademark claims. An outside party could attempt to control a public domain work via patent or trademark law.[23] Open-source licenses, even very permissive licenses like the BSD license, disclaim warranty and liability. Anyone using open-source software must accept this disclaimer as a condition, but public domain waivers cannot impose a disclaimer of warranty and liability.[20]


Freeware is software distributed at no cost. Open-source software is often free, but "freeware" commonly refers to proprietary software. Proprietary software licenses do not grant permission to modify and redistribute the software. Proprietary freeware licenses limit redistribution, prohibit commercial usage, and limit installations.[24] Rather than an open-source license that facilitates collaborative development, proprietary freeware often comes with an end-user license agreement that prohibits users from developing the software. Freeware is part of the business model of major proprietary software vendors. For example, in 2014, Microsoft was the world's largest supplier of freeware.[25] Source-available software is a marketing term for proprietary freeware that comes with source code as a reference and not as a basis for derivative works.[26]

See also[edit]


  1. ^ Fagundes & Perzanowski 2020, p. 529.
  2. ^ Rosen 2004, Chapter 2.
  3. ^ Oman 2018, p. 641.
  4. ^ Williams 2002.
  5. ^ Raymond 1998, "Specifically, we have a problem with the term "free software", itself, not the concept,".
  6. ^ Raymond 2001, p. 19.
  7. ^ a b Rosen 2004.
  8. ^ Sen, Subramaniam & Nelson 2008, pp. 211–212.
  9. ^ Rosen 2004, p. 69.
  10. ^ Rosen 2004, pp. 101–102.
  11. ^ Rosen 2004, pp. 73–90.
  12. ^ Tsai 2008, pp. 569.
  13. ^ Joy 2022, pp. 990–992.
  14. ^ Rosen 2004, pp. 103–109.
  15. ^ Tsai 2008, pp. 564–570.
  16. ^ Sen, Subramaniam & Nelson 2008, pp. 212–213.
  17. ^ Stallman 2021, "For the free software movement, free software is an ethical imperative,".
  18. ^ Perens 1999, "Although it is not promoted with the same libertarian fervor, the Open Source Definition includes many of Stallman's ideas, and can be considered a derivative of his work. The Open Source Definition started life as a policy document of the Debian GNU/Linux Distribution,".
  19. ^ Stallman 2021, "First, some open source licenses are too restrictive, so they do not qualify as free licenses. For example, Open Watcom is nonfree because its license does not allow making a modified version and using it privately,".
  20. ^ a b Rosen 2004, p. 36.
  21. ^ Rosen 2004, pp. 74–77.
  22. ^ Fagundes & Perzanowski 2020, p. 524.
  23. ^ Joy 2022, pp. 1008–1010.
  24. ^ Corbly 2014, pp. 2–4.
  25. ^ Corbly 2014, pp. 5–6.
  26. ^ Kunert 2022.


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