Permissive free software licence

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"Copycenter" redirects here. For a place to make copies of documents, see photocopier.

A permissive free software licence is a class of free software licence with minimal requirements about how the software can be redistributed. Such licenses therefore make no guarantee that future generations of the software will remain free. This is in contrast to licences which have reciprocity / share-alike requirements.[1] Both sets of free software licences offer the same freedoms in terms of how the software can be used, studied, and privately modified. A major difference is that when the software is being redistributed (either modified or unmodified), permissive licences permit the redistributor to restrict access to the modified source code, while sharealike licenses do not allow this restriction. A more narrowly constrained term related to permissive licensing is copyfree,[2] which implies distinct licence term requirements analogous to, but different from, those of free software.

Well-known examples of permissive free software licences include the MIT License and the BSD licenses. A well known sharealike free software license is the GNU General Public License.

Comparison to public domain[edit]

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, permissive licences are not actually equivalent to releasing a work into the public domain.

Permissive licences 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,[3] and attribution may still be considered an ethical requirement in academia.

Comparison to copyleft[edit]

Further information: Copyleft

Copyleft is a sharealike license type, "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."[4] By comparison with permissive licences, sharealike licensing places more requirement in terms of distribution and combination with software under other licences. Specifically copyleft prohibits freedom to change the license and freedom to strip the granted freedoms.

Other terms[edit]


Copycenter is a term originally used to explain the modified BSD license, a permissive free software licence. The term was presented by Kirk McKusick, a computer scientist famous for his work on BSD, during one of his speeches at BSDCon 1999. It is a word play on copyright, copyleft and copy center.

The way it was characterized politically, you had copyright, which is what the big companies use to lock everything up; you had copyleft, which is free software's way of making sure they can't lock it up; and then Berkeley had what we called ‘copycenter’, which is ‘take it down to the copy center and make as many copies as you want.’

The liberty to 'make as many copies as you want' is in fact also provided by all copyleft licences. However, unlike both copyleft licences and copyright law, permissive free software licences do not control the licence terms that a derivative work falls under.


Copyfree logo

The Copyfree Initiative defines Copyfree as a type of permissive copyright license which falls under their Copyfree Standard Definition.[2]

Copyfree licenses include the Simplified BSD license, the Open Works license, and others, but not the GNU GPL or other copyleft licenses. The Creative Commons CC0 public domain dedication is also considered to be copyfree.[6]

While all copyfree licenses are permissive licenses, not all permissive licenses are copyfree, since they may introduce limitations not allowed under the copyfree definition. The Apache License 2.0 (as well as previous versions of this license) is an example of a non-copyfree permissive license.[7] Another notable example is the Creative Commons Attribution 3.0 license, which is also incompliant with the Copyfree Standard Definition because the licence forbids DRM technologies.

Copyleft compatibility[edit]

Some permissive free software licences contain clauses that make them incompatible with copyleft licences. One example is clauses requiring advertising materials to credit the copyright holder. Licences with this type of advertising clause include the 4-clause BSD license, the PHP License, and the OpenSSL Licence.

Examples of permissive free software licences without advertising clauses are the MIT License, the 3-clause BSD license, and the Zlib License.

Some licences 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 licence incompatible with permissive free software licences.

See also[edit]

External links[edit]


  1. ^ "Categories of free and nonfree software". 
  2. ^ a b "Copyfree Standard Definition". Copyfree Initiative. 
  3. ^ US Copyright Office Form CO; see also Ashton-Tate v. Fox
  4. ^ "What is Copyleft". GNU. Retrieved 21 April 2011. 
  5. ^ The Jargon File contributors (2006). "copycenter". The Jargon File. Eric S. Raymond. Retrieved June 14, 2006. 
  6. ^ Anonymous. Copyfree Licenses. Copyfree. . URL: Accessed: 2013-04-29. (Archived by WebCite® at
  7. ^ "Copyfree: standard > rejected". Copyfree Initiative. Retrieved 2014-10-26. Section 4, subsections 2 and 4 of the Apache License 2.0 violate point 3. Free Modification and Derivation of the Copyfree Standard Definition by specifying conditions (beyond licensing) that must apply to modifications.