Recommended and required criteria
This definition uses the terms may, may not and must not in obvious ways to distinguish required and optional criteria for covered licenses. Importantly, it uses the term should where we recommend that licenses which do not meet the stated criteria should be amended. Later versions of this definition may make some of these criteria mandatory.
In order to be recognized as "free" under this definition, a license must grant the following freedoms without limitation:
- The freedom to study and apply the information: The licensee must not be restricted by clauses which limit their right to examine, alter or apply the information. The license may not, for example, restrict "reverse engineering", and it may not limit the application of knowledge gained from the work in any way.
- The freedom to redistribute copies: Copies may be sold, swapped or given away for free, as part of a larger work, a collection, or independently. There must be no limit on the amount of information that can be copied. There must also not be any limit on who can copy the information or on where the information can be copied.
- The freedom to distribute modified versions: In order to give everyone the ability to improve upon a work, the license must not limit the freedom to distribute a modified version, as above, regardless of the intent and purpose of such modifications. However, some restrictions may be applied to protect these essential freedoms, as well as the requirement of attribution (see below).
Allowed requirements and restrictions
There are certain restrictions on the use or interchange of works that we do not feel impede on the essential freedoms enumerated above. These are described below.
Attribution protects the integrity of an original work, and provides credit and recognition for authors. A license may therefore require attribution of the author or authors, provided such attribution does not impede normal use of the work. For example, it would not be acceptable for the license to require a significantly more cumbersome method of attribution when a modified version of the licensed text is distributed.
Protection of freedoms
The license may include clauses that strive to protect the essential freedoms of the work, such as:
- transparent copies: a clause requiring all copies of the work to be in a transparent file format (documented and not encumbered by patents) which allows the work to be freely used in perpetuity
- copyleft or "share-alike": a clause requiring that derivative works are entirely made available under a license which meets this definition
- free from technical restrictions: a clause prohibiting the use of technical measures designed to prevent individuals to whom the work is distributed from exercising any of the freedoms described above
The license may not include clauses that strive to limit the essential freedoms of the work, such as:
- usage restrictions: the license must not limit the licensee's actions beyond those which may have a plausible and direct impact on the essential freedoms of the work or its derivatives. Explicitly, it must not limit commercial use of the work.
Authors of licenses should make an effort to gradually make licenses which share the same philosophical roots and legal principles compatible with each other to ensure that works under these licenses can be combined and aggregated freely. This may be accomplished by altering the terms of the license (e.g. by removing a restriction which the other license does not have), or by adding migration clauses which allow the use of the licensed work under the now compatible license.
When making copies of a work, the licensee should be allowed to refer to a resource pointer instead of being required to distribute the license text itself with each copy of the work. Similarly, the license should allow the author or authors to specify a resource pointer for the attribution of multiple authors of a work. This is to ensure that the attribution requirement for complex collaborative works does not become an impediment.
- See Licenses for discussion of individual licenses, and whether they meet this definition or not.
- See History for acknowledgments and background on this definition.
- See the FAQ for some questions and answers.
- See Portal:Index for topic-specific pages about free content and free expressions.
- Under some jurisdictions, notably some European countries, authors have inalienable moral rights and cannot completely release their works into the public domain. If you believe that you have a right to put your own works in the public domain, regardless of what the law says, you can make a declaration of public domain status which contains a safeguard clause, such as: "I, the author of this work, hereby release it into the public domain. This applies worldwide. In case this is not legally possible: I grant anyone the right to use this work for any purpose, without any conditions, unless such conditions are required by law."