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I believed that Creative Commons Attribution License, even being non-copyleft one, was always and still is incompatible with GNU GPL because of multiple minor issues; which, however, were gradually resolved from version to version: early versions of CC BY were hardly free at all; now, as far as I understand, the only unusual for a free software license clause of CC BY 4.0 is its key point: attribution requirements.

I know, that Creative Commons is now working together with the FSF on making current version of its copyleft license, CC BY-SA 4.0, compatible with GNU GPL. That is a formal process, somewhat similar to publishing a new license version; if it would succeed, there should be an announcement from CC, as it was when CC BY-SA 4.0 was declared mutually compatible with the Free Art License v1.3.

As far as I know, there was no such process for CC BY. However, firstly, a week ago, along with updating links from v2.0 of CC BY to v4.0, a statement about incompatibility of CC BY with GNU GPL and GNU FDL was removed by FSF Licensing & Compliance Manager Joshua Gay from a ‘Various Licenses’ list on www.gnu.org, which is used as authoritative source on GPL-compatibility; and secondly, two days ago an explicit note that “CC BY 4.0 is compatible with GPLv3” was added without any noticeable announcement or explanation, as if it is something obvious.

Is it indeed so obvious? Fourth generation of CC license zoo is about one year old, why only now? And how shall I consider attribution obligations when incorporating a work under CC BY into a work under GPLv3? I guess, as additional requirements under section 7b of the GNU GPLv3:

Notwithstanding any other provision of this License, for material you add to a covered work, you may (if authorized by the copyright holders of that material) supplement the terms of this License with terms:
<...>
b) Requiring preservation of specified reasonable legal notices or author attributions in that material or in the Appropriate Legal Notices displayed by works containing it...

These were rhetorical questions though. Now the actual question.

I do not understand very well how transitive CC licenses (since second generation) are: are previous versions of CC BY: 2.0, 2.5 and 3.0; indirectly compatible with GNU GPLv3 now?

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    Based on the guidelines for upgrading to CC-BY 4.0, a work cannot "upgrade" its license unless such an upgrade is expressly authorized by the copyright holder (e.g., by "3.0 or later" language or by explicit re-licensing). Decisions about compatibility for 4.0 would not affect previous versions (unless the criteria for those decisions matched the situation for a previous version exactly). – apsillers Feb 6 '15 at 16:36
  • @apsillers, hmm... Indeed, this page states that the work cannot be sub-licensed under the next version; it’s only allowed to combine works under different versions of CC BY-SA (that seems to be important to CC BY-SA only, since CC BY already allows much more restrictive combinations). How did StackExchange change a license on user contributions from CC BY-SA 2.5 to 3.0 few years ago then, I wonder. – Dmitry Alexandrov Feb 6 '15 at 20:08
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    Next time, please do not indulge in "rhetorical questions" as this site is expected to have genuine questions. I've just spent about 2 hours tracking the correlations between the FSF's edit and the CC's initiative and got ready to publish my findings, only to find out this all was but idle talk irrelevant to the real matter. – ivan_pozdeev Feb 24 '15 at 16:43
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    Well, I know what to do. I'll publish my findings along with the material on the actual question once I accumulate it. And let you go figure out which phrases are relevant to which. – ivan_pozdeev Feb 24 '15 at 16:51
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Joshua Gay's edit looks sloppy at best: I found at least 2 clauses and a section in http://creativecommons.org/licenses/by/4.0/legalcode that look incompatible with any GPL. I've written a letter to the FSF asking them to clarify this matter and the properties of the edit.

This is what I just got in reply, from none other than Joshua himself (nested blocks are his quotes from my letter):

Hello,
Thank you for writing.

  • It doesn't mark the license as "compatible with the GNU GPL or FDL" with the left-side line.

The color doesn't specify a version number of the GPL. I have been waiting for confirmation from our general counsel that CC BY is incompatible with GPLv2 and the FDL before updating the color on the left hand side. Hopefully that will be soon.

First note that both licenses make use of words like reasonable and within reason. Interpretation should be done with that in mind. Here is our position on this as I understand it. You are right that we should have a more formal statement and I will try to get one prepared that we publish on the site.

GPLv3 7(b) states that you can add terms "Requiring preservation of specified reasonable legal notices or author attributions in that material or in the Appropriate Legal Notices displayed by works containing it;"

The FSF interprets this as to include a licensor doing something such as removing certain parts of the reasonable legal notices or marking them in ways as different from the original.

How are they unclear? I do not see what is unclear.

A person does not need to relicense a work to create a combined work with the GPL. A CC BY licensed work that is incorporated into a GPL licensed work would retain a copy of the CC BY license and all CC BY notices. One would simply add to the work as a whole and in relevant plces notices about the GPL and a copy of the GPL.

CC BY does not restrict adding additional terms so long as those additional terms do not restrict "exercise of the Licensed Rights by any recipient of the Licensed Material."

I will see about adding these clarifications somewhere.
Thanks again for emailing us.

Joshua Gay
Licensing & Compliance Manager
Free Software Foundation

This is the reply I got on further clarification of CC#s3a3. He believes it's compatible by doing a narrow interpretation:

The incompatibility as it appears to me is that GPL gives no right to change any terms for a licensee who has already received a license (or receives it from an older copy) - since a license is irrevocable and is granted on the terms that accompany a specific copy.

So, your interpretation of this CC clause is that it only applies to the moment one receives a copy from the copyright holder, not to any later moment or receiving it from any other party?

That is my current understanding. Do I have a reason to think it would mean at a later date? I assumed such a request would need to be made alongside the license itself. I will ask Creative Commons what their interpretation is.

I am not a lawyer and I have no ideas how courts would interpret this. But, I'm not sure how one could reasonable expect a work to be put into the wild, modified and remixed for a period of 75 or 80 years and then it be reasonable that a licensor could come along and ask for all of those notices to be removed.

And here's the final update, right from the horse's mouth. The "reference removal" CC clause is an obstacle. But as of now, Joshua doesn't consider it a strong enough one to condemn CC-BY as incompatible. (diff to the current licenses.html as of this writing)

I suspect the clause does have such a use in mind. Its intended use appears to be the case where a copyright holder sees their work used in a context that they deem inappropriate - so they wish any reference to them removed so that their perceived reputation doesn't suffer.

Creative Commons sent me a clarification and it is the case that the intent of the license is so that a user could ask after the fact. However, they explained that "to the extent reasonably practicable" gives a person a lot of flexibility in being able to simply deny the request of the original licensor. I am interested in finding out some other legal opinions on how strong the language "to the extent reasonably practicable". Like how easy it is to make that argument as a licensee. I believe this is will be the next question in the public discussion mailing list. I will also open up an internal discussion at the FSF and with our lawyers to make sure they think the language "reasonably practicable" is sufficiently strong.

Why did he make the edit when he did? Perhaps because that's when he checked the compatibility. He actively participates in the CC-BY-SA - GPLv3 compatibility effort - that could very well be the reason that drew his attention to that matter.

The "transitive" compatibility of the earlier versions of the CC-BY has already been well explained by apsillers:

Earlier licenses are incompatible on their own but are compatible if the work's license allows relicensing to a compatible version. As you can see, this is a general principle not specific to a license.

  • I am very intrigued, what are these two clauses and a section of CC BY you find incompatible with GNU GPL? – Dmitry Alexandrov Feb 26 '15 at 20:00
  • Glad you asked! Adding the answer from none other than Joshua Gay himself! – ivan_pozdeev Feb 26 '15 at 22:03
  • I've requested some more clarification for the s3a3 clause. – ivan_pozdeev Feb 26 '15 at 23:44
  • Here it is. Guess this is enough to address all the matters in the question. – ivan_pozdeev Feb 27 '15 at 8:17
  • Here's the final update. – ivan_pozdeev Mar 3 '15 at 2:46

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