The GNU General Public License (GPL version 2) is the slightly modified successor the oldest reciprocal license (the GPLv1).

An overview for further reading on the GPL:

  • Die GPL kommentiert und erklärt (Till Jaeger et. al, O'Reilly März 2005)
  • Lawrence Rosen on the GPL Chapter 6
  • Thomas F. Gordon on general license combatibility
  • Lothar Determan - Software combinations as Derivative works?
  • OSI compliance

    With a strict view on the OpenSource definition, the GPL would be a non-free license. In GPL section 8, it is permitted to add a clause that could restrict the GPL to give it's permission only to specific groups, but this would be in conflict with section 5 of the OpenSource definition. Fortunately, there is no actual software that makes use of GPL section 8, so all currently existing GPLd software is compliant to the OpenSource definition.

    License type

    The GPL is a reciprocal license with a strong Copyleft


    The GPL gives patent grants but does it contain rules that help to defend against patent trolls.

    The GPL and collective vs. derivative works

    The FSF (creator of the GPL) is very eager with explaining that the GPL is not a "contract" but a "license" under US law, see this article. For this reason, the GPL may only rightfully contain claims that are permitted by US Copyright law title 17 paragraph 106 The right to define what's a derivative work is not amongst these grants from the US Copyright law. As a result, the definitions for collective and derivative works from the US Copyright law apply.

    So fortunately, most real world issues with the GPL refer to collective works where independent works just link against each other. This is clearly permitted by the GPL.

    A derivative work is a work made from one or more independent works and where a modification of significant own creation is added. Modifications of minor importance/creation are not Copyrightable and do not create a derivative work but just a variant of the original work. In a derivative work that matches the definitions from the Copyright law, the GPL requires the the modifications to be put under GPL.

    In contrary to that, a collective work is a work created from the combination of several independent works.

    It is thus obvious that edits of a pure GPL work typically create a derivative work and that combinations from a GPL work with another work under a different license typically create a collective work.

    The GPL and the community

    The GPL is the most successful OSS license but there is few unbiased information on the GPL available in the net. Some unbiased information may be found in: Lawrence Rosen on the GPL Chapter 6 and Thomas F. Gordon on general License compatibility. As these papers explain, several of the important claims of the GPL are in conflict with the Copyright law and thus will most likely not stand in court. For this reason it is questionable whether it makes sense to use a license that includes restrictions that appear to be useless. Since a few years, there are other reciprocal (Copyleft) licenses that avoid to make those restrictive claims of questionable value.

    The GPL in collaborative works

    The GPL prevents code flow from code under GPL into other works being under different even OSI compliant licenses. Note that the GPL still permits collective works and thus allows linking against other independent works as long as this may be achieved by linking unmodified works or only slightly modified works.

    As the GPL impairs collaboration and as the GPL, does not contain a method to defend against patent suing, the OSSCC does not recommend to use the GPL for new projects.

    The GPLv3

    The GPLv3 has been published in June 2007. The GPLv3 no longer contains claims that are comparable to section 8 of the GPL, so the GPLv3 is a true OSS license. The GPLv3 added claims to defend against patent suing. Unfortunately, the GPLv3 tries to add further restrictions on collective works and as this is done by using an ambiguous wording, it is expected to create a high risk to distributors for being sued by authors or Copyright holders.

    As the GPLv3 impairs collaboration even more than the GPL, the OSSCC does not recommend to use the GPLv3 for new projects.
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