When someone adapts a BY-SA work and applies the FAL to her contributions, both licenses apply and downstream users must comply with both. However, because of Section 2(a)(5)(B) of BY-SA 4.0, anyone who receives the adapted material downstream may satisfy the conditions of both BY-SA and FAL (i.e. attribution and ShareAlike) in the manner dictated by the FAL.
When someone adapts an FAL work and applies BY-SA 4.0, the the terms and conditions of the BY-SA 4.0 license apply to the entire work, including those elements originally licensed under the FAL. As in the BY-SA to FAL scenario, however, both authors must be attributed.
For more information, see the compatibility-specific FAQs and explanatory information here.
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 two licenses have slightly different attribution and marking requirements. The FAL has fewer total requirements than BY-SA, but it does have some requirements that are not included in BY-SA.
The FAL requires:
CC determined that the minor differences in attribution and marking requirements were not significant enough to disrupt licensor expectations or cause problems for licensees.
The FAL licenses copyright and performance rights, though licensors are prohibited from using related rights to prevent exercise of the permissions granted by the license. BY-SA 4.0, on the other hand, licenses some rights beyond copyright, such as sui generis database rights and neighboring rights. Unlike the FAL, BY-SA requires compliance with its conditions (attribution, ShareAlike) even when only those other rights, and not copyright, are being exercised by the reuser.
For compatibility purposes, when someone adapts a BY-SA work and applies the FAL to their contribution, there is a possibility that a downstream user may not realize they need to attribute and comply with the ShareAlike condition when they exercised a right other than copyright covered by BY-SA before sharing it. As a practical matter, however, we feel this is unlikely to be a major problem given that most reusers will either be unwilling or unable to discern when one type of right is implicated but not another closely related right. Accordingly, we expect most reusers are likely to attribute and/or ShareAlike where there is uncertainty.
Unlike BY-SA, the FAL does not explicitly prohibit the application of DRM or other effective technological measures ("ETMs") to the licensed work, but it prohibits users from doing anything that prevents others from exercising the license freedoms. Because this implicitly disallows ETMs, we feel this difference is not significant enough to preclude a compatibility determination.
Unlike BY-SA, the FAL does not have a provision allowing licensees to automatically get their rights back under the license after they correct a violation. When a BY-SA work is adapted and the FAL is applied, at worst, licensees will not realize their rights are automatically reinstated under certain circumstances. We do not feel this is an obstacle to compatibility.
The FAL gives licensees the option to comply with a later version of the FAL, regardless of whether the work has been adapted. BY-SA, on the other hand, 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. When a BY-SA work is adapted and the FAL is applied, licensees may attribute and ShareAlike according to the conditions of the FAL 1.3. The FAL provision giving the option to comply with later versions should not affect licensees' obligations vis-a-vis BY-SA 4.0 unless and until later versions of the FAL are deemed compatible to BY-SA 4.0.
Creative Commons consulted extensively with the steward of the Free Art License during the 4.0 versioning process, as well as throughout the compatibility process on the policy matters described above. Especially where two-way compatibility is at issue, the opinions, interpretations, and support of the candidate steward are critical components of CC's analysis, as are the support and expectations of the community the steward serves. The final determination and policy statements above reflect the best interpretations by both stewards of their respective licenses.