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Permissive software license

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A permissive free software licence is a free software license that applies to an otherwise copyrighted work. It also offers many of the same rights found in free software licenses when releasing a work to the public. In contrast to non-permissive copyleft (reciprocal) licenses such as the GNU General Public License, any copies and derivatives of the source code created under permissive licenses may be made available on terms that are more restrictive than those of the original license. For example, source code released under a permissive software license does not have the requirement that all distributed derivatives also be made available to the public.

Well-known examples of permissive licenses include the MIT License and the BSD licenses.

Comparison to public domain

Computer Associates Int'l v. Altai 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, such 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 (attribution). 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,[1] and attribution may still be considered an ethical requirement in academia.

Comparison to Copyleft

Further information: Copyleft

What is Copyleft

Copyleft is a play on the existing term "Copyright, implying a reversal of the policies suggested by Copyright. According to Free Software Foundation:

"Copyleft is a general method for making a program or other work free, and requiring all modified and extended versions of the program to be free as well.The simplest way to make a program free software is to put it in the public domain, uncopyrighted. This allows people to share the program and their improvements, if they are so minded. But it also allows uncooperative people to convert the program into proprietary software. They can make changes, many or few, and distribute the result as a proprietary product. People who receive the program in that modified form do not have the freedom that the original author gave them; the middleman has stripped it away."[2]

Contrast With Copyfree

In addition to the Four Freedoms defined by GNU project that are necessary to define a software (or other works) as a "Free Software", copyleft licenses also have the following two characteristics:

  1. Strong heritability characteristics. Any code that is combined with copyleft code must also be licensed under the same copyleft terms. A license could be considered "strong" where linked contents must be distributed under the same license, or "weak" where a copyleft license can coexist with other licenses within the same project but not the same files.
  2. Restrictions on forms of distribution. When the work is distributed under the terms of a copyleft licence, users must be able to have access to its source code and should be informed of the availability of the source code.

Compared with Copyfree, copyleft licensing places more restrictions and demands in terms of distribution and combination with other licenses. Copyfree and coplyleft also have different policies on usages, including business use and code reuse.

GPL compatibility

Some permissive free software licenses contain clauses that require advertising materials to credit the copyright holder. Licenses with an advertising clause include the 4-clause BSD license, the PHP License, and the OpenSSL License. These licenses, although they are permissive free software licenses, are incompatible with the widely used GNU General Public License.

Examples of permissive free software licenses without advertising clauses are the MIT License, the 3-clause BSD license, the Zlib License, and all versions of the Apache License except 1.0.

Some licenses do not allow derived works to add a restriction that says a redistributor cannot add more restrictions. The purpose of such clauses is to disallow redistribution using the GPL or similar copyleft licenses.[citation needed] There are many examples such as the CDDL and MPL. However such restrictions also make the license incompatible with the BSD license.

See also

Wikibooks has a book on the topic of: FOSS Licensing

References

  1. ^ US Copyright Office Form CO; see also Ashton-Tate v. Fox
  2. ^ "What is Copyleft". GNU. Retrieved 21 April 2011.
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