This page documents the primary decisions made by Creative Commons when considering the GNU General Public License version 3 (the "GPL") for one-way ShareAlike compatibility pursuant to the compatibility process and criteria.
When someone creates an adaptation of a BY-SA licensed work and includes it in a GPLv3-licensed project, both licenses apply and downstream users must comply with both licenses. However, Section 2(a)(5)(B) of BY-SA 4.0 allows anyone who receives the adapted material downstream to satisfy the conditions of both BY-SA and GPLv3 (i.e. attribution and ShareAlike) in the manner dictated by the GPLv3.
People may *not* adapt a GPLv3-licensed work and use BY-SA to license their contributions. This is not allowed by GPLv3. Thus, this compatibility determination only allows movement one way, from BY-SA 4.0 to GPLv3.
For more information, see the compatibility-specific FAQs and explanatory information here. We also encourage you to read this list of considerations before applying the GPLv3 as the adapter’s license.
In 2008, Creative Commons published the CC Attribution-ShareAlike Statement of Intent, in which CC articulated its intentions as steward for the SA licenses. In point 4 of the statement, CC commits that "any candidate for compatibility must also satisfy the definition of a Free Cultural License set out in the Definition of Free Cultural Works." This criteria serves as the initial gatekeeping factor for all candidate licenses.
The specific attribution and marking requirements in the two licenses vary slightly.
BY-SA 4.0 requires:
If you change the work, BY-SA also requires you to indicate that you did so and retain any notice on the work about previous changes made to it. BY-SA requires reusers to remove attribution if practicable when requested by the licensor.
If you change the work, GPL requires you include a prominent notice to indicate that you did so, along with the relevant date. It also requires special notices for certain interactive user interfaces. GPLv3 does not have an attribution removal clause.
When BY-SA 4.0 content is adapted and used in a GPLv3-licensed project, the adapter has to comply with the BY-SA attribution and marking requirements. However, Section 2(a)(5)(B) of BY-SA 4.0 enables downstream reusers of the GPL-licensed project to look to the GPL to satisfy their obligations under both licenses. CC determined that GPL-style attribution would satisfy the expectations of BY-SA licensors.
The tone and scope of the two licenses differ, due largely to the fact that the GPLv3 was designed for use with software and software-like works. Both licenses are primarily designed to license copyright, but each license also covers some rights closely related to copyright. GPL covers “copyright-like laws that apply to other kinds of works, such as semiconductor masks,” while BY-SA covers “Copyright and Similar Rights,” which is defined to include neighboring rights, sui generis database rights, and other closely-related rights.
The most significant difference in license scope is the treatment of patent rights. BY-SA expressly reserves patent rights to the licensor, while GPLv3 expressly includes a patent grant from each contributor.
Because patent rights are expressly excluded from BY-SA, there is no reliable claim of an implied license to do things with a BY-SA licensed work that implicate patent rights. From a compatibility perspective, this means that when a BY-SA work is adapted and included in a GPL-licensed project, downstream users of the project would not have patent rights (if any) to the adapted BY-SA work. (Although the GPL includes a patent license, the scope of rights licensed by the BY-SA licensor cannot be unilaterally expanded by an adapter who choses to apply the GPL, just as it is not expanded when an adapter applies a later version of BY-SA that licenses more rights than the original.)
This creates the possibility that a downstream user of a GPL project will mistakenly assume that all patent rights are treated as they are in GPLv3 when in fact they are not. We have determined, however, that this should not prevent a determination of one-way compatibility because it is largely an academic problem. Rarely (if ever) would a BY-SA work be subject to patent rights that would be implicated by reproducing or adapting the content.
The GPL requires that works be distributed with source or that source be made available (with “source” being the preferred form for making modifications to the work). BY-SA does not impose a similar requirement. Instead, BY-SA licensors are free to distribute their works in any format, whether or not modifiable.
With one-way compatibility to the GPL, no new obligations are imposed under the BY-SA license, either upon the original licensor or any downstream adapter who wishes to license their contributions under the GPL instead of BY-SA. However, those who adapt BY-SA works and choose to license their contributions under the GPL do, however, have to comply with the GPL obligation to distribute or make available the work in the preferred form for making modifications. If an adapter cannot provide or make available source either because she never received the work in modifiable format from the BY-SA licensor or cannot convert the content to modifiable format, then that person cannot take advantage of the one-way compatibility declaration and use the GPLv3 for her contributions.
BY-SA prohibits application of ETMs by licensees if those measures would prevent others from exercising their rights under the license. In contrast, the GPL does not explicitly prohibit application of DRM and other ETMs. Instead, it addresses any potential lockdown of licensed works by requiring distribution of source code in a modifiable form.
This difference is not problematic, because in order to comply with GPLv3 the adapter must provide source. As stated in the previous section, if an adapter cannot provide or make source available, she cannot take advantage of the one-way compatibility declaration and may not use GPLv3 for her contributions.
Both licenses terminate automatically upon breach. BY-SA 4.0 is reinstated automatically if the violation is cured within 30 days of discovery, whether it is the first violation or one of several subsequent violations. GPLv3 is reinstated automatically for first-time violators who cure within 30 days of receiving notice of the violation from the copyright holder, and is reinstated after subsequent violations if it has been corrected for 60 days without the licensor's objection. This difference means that a user of a combined BY-SA adaptation and GPL work may have the right to use some portion but not all portions of the larger work, depending on whether rights have been reinstated under the respective licenses. In practice, however, this difference is not overly problematic and is not be an obstacle to declaring one-way compatibility, since the large majority of licensors and licensees in both communities resolve license violations amicably.
GPLv3 gives licensees the option to comply with a later version of the GPL if the licensor has so specified, or to use *any* version of the GPL if no version number was specified, regardless of whether the work has been adapted. BY-SA 4.0 allows licensees to comply with the conditions of future versions of BY-SA, but only if that version was applied to an adaptation of the work. Because this compatibility determination is limited to version 3 of the GPL, reusers that adapt BY-SA 4.0 content and incorporate it into GPL-licensed projects are only able to use GPLv3 unless and until other GPL versions are declared compatible. With solid education for both communities and encouragement of clear marking by licensors, we do not feel this is an obstacle to compatibility.
GPL licensors who are concerned with enabling use under later versions do have the option of using the proxy provision in the GPLv3 to address this limitation. Section 14 of GPLv3 allows licensors to specify a proxy to determine whether future versions of the GPL can be used. Therefore, if someone adapts a BY-SA 4.0 work and incorporates it into a GPLv3-licensed project, they can specify Creative Commons as their proxy (via http://creativecommons.org/compatiblelicenses) so that if and when Creative Commons determines that a future version of the GPL is a compatible license, the adapted and combined work could be used under that later version of GPL.
Creative Commons consulted extensively with the Free Software Foundation during the 4.0 versioning process, as well as throughout the compatibility process on the policy matters described above. The final determination and policy statements above reflect the best interpretations by both stewards of their respective licenses.
Because of the limited one-way nature of this compatibility determination and because GPLv3 is designed for software, there are a few particular considerations to take into account before applying the GPLv3 as the adapter’s license when adapting BY-SA 4.0 works.