Permissive software license
A permissive software license, sometimes also called BSD-like or BSD-style license, 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. the most popular free-software license is the permissive MIT license.
Example
The following is the full text of the simple GNU All-permissive License:Definitions
The Open Source Initiative defines a permissive software license as a "non-copyleft license that guarantees the freedoms to use, modify and redistribute". GitHub's choosealicense website describes the permissive MIT license as " people do anything they want with your code as long as they provide attribution back to you and don’t hold you liable." 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."Comparison to copyleft
| Public domain & equivalents | Permissive license | Copyleft | Noncommercial license | Proprietary license | Trade secret | |
| Description | Grants all rights | Grants use rights, including right to relicense | Grants use rights, forbids proprietization | Grants rights for noncommercial use only. May be combined with copyleft. | Traditional use of copyright; no rights need be granted | No information made public |
| Software | PD, CC0 | BSD, MIT, Apache | GPL, AGPL | JRL, AFPL | proprietary software, no public license | private, internal software |
| Other creative works | PD, CC0 | CC-BY | CC-BY-SA | CC-BY-NC | Copyright, no public license | unpublished |
Copyleft licenses generally require the reciprocal publication of the source code of any modified versions under the original work's copyleft license. 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. As a result, derivative works, or future versions, of permissively-licensed software can be released as proprietary software.
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.
Comparison to public domain
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. 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, 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. 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
In general permissive licenses have good licence compatibility with most other software licenses in most situations.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, several authors noted an increase in the popularity of permissive licenses during the 2010s.the MIT licence, a permissive license, is the most popular free software license, followed by GPLv2.