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The FAQ on the Creative Commons website states:

Can I apply a Creative Commons license to software?

We recommend against using Creative Commons licenses for software. Instead, we strongly encourage you to use one of the very good software licenses which are already available. We recommend considering licenses listed as free by the Free Software Foundation and listed as “open source” by the Open Source Initiative.

Unlike software-specific licenses, CC licenses do not contain specific terms about the distribution of source code, which is often important to ensuring the free reuse and modifiability of software. Many software licenses also address patent rights, which are important to software but may not be applicable to other copyrightable works. Additionally, our licenses are currently not compatible with the major software licenses, so it would be difficult to integrate CC-licensed work with other free software. Existing software licenses were designed specifically for use with software and offer a similar set of rights to the Creative Commons licenses.

...

While we recommend against using a CC license on software itself, CC licenses may be used for software documentation, as well as for separate artistic elements such as game art or music.

from https://creativecommons.org/faq/#can-i-apply-a-creative-commons-license-to-software

This seems to recommend not using any CC licenses for software. But the reasons for this recommendation listed in the second paragraph do not seem relevant when examining a software license such as the MIT license. The MIT license does not mention source code or patents and the CC-BY license seems compatible with the MIT license. For me, this begs the question "How is using CC-BY any different than using MIT?" (with respect to the license's functionality). There must be a functional difference in the CC-BY and MIT license that would explain why CC-BY shouldn't be used for software.

This question is similar to the question:

Why is CC BY-SA discouraged for code?

but it discusses the CC-BY-SA license which has more complexities than CC-BY. This question does mention "License Proliferation" and I understand that could be a concern here, but since the CC licenses are so widely used I don't find it a compelling argument as to why not to use CC licenses. Thus, I'm interested in an answer other than "to prevent license proliferation" if there is one.

My motivation for this questions is that I have creative works that are collectively made up of software, images, written text, animations that I'd like to group and license in a liberal way. Applying the CC-BY license to the entire set of items in the work seems like the appropriate thing to do, rather than using the MIT license alone which is only for code & documentation or using multiple licenses for the different content types.

So, why does Creative Commons recommend not using CC-BY licenses for software?

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    I can't say for sure. As an open source user, maintaining a code base with contributions from many people requires maintaining a list of "BY" people who contributed, which would be a pain for large projects. For that reason I'd stay away from any CC-BY and prefer 3-Clause BSD or Apache 2.0. They have fewer encumbrances (headaches) that way. – markspace Jan 20 at 1:46
  • Are you suggesting that CC-BY requires you to list the people who contributed and BSD & Apache do not? – moorepants Jan 20 at 2:05
  • Yup. There's no "attribution required" clause in either of those. While author's names are typically left in the comments, there's no requirement, and many contributions are anonymous. – markspace Jan 20 at 2:14
  • I'm not seeing anywhere in the CC-BY 4.0 license that says you are required to list the names of the copyright holders in any specific way. It seems to say that the licensor can specify the creator(s) however they want, e.g. "Software Project Authors". – moorepants Jan 20 at 2:24
  • There's a link in the license which goes into more detail about "attribution required" wiki.creativecommons.org/wiki/… – markspace Jan 20 at 2:29
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The main reason why Creative Commons recommends against using CC licenses, including CC-BY, for software is probably license proliferation.

Another issue is that, even for an apparently simple license like CC-BY, it is not entirely clear how that license interacts with other licenses and where the incompatibilities lie.

For example, the legalcode contains the clause

  1. Downstream recipients.

    [...]

    b. No downstream restrictions. You may not offer or impose any additional or different terms or conditions on, or apply any Effective Technological Measures to, the Licensed Material if doing so restricts exercise of the Licensed Rights by any recipient of the Licensed Material.

This reads to me, and I am not a lawyer, that you can't use CC-BY material in a completely closed-source product. That makes the CC-BY license closer to a weak copyleft license (like the MPL or LGPL) than a permissive license (like MIT or Apache 2.0).

And there are probably other points where the formal legal text of the CC-BY license has effects that are contrary to the initial looks and possibly surprising when used in a software context.

  • Good find. With MIT licensed code, one can modify it and bundle it in closed-source binary that you distribute and you only have to include the original license text alongside that binary. But this clause does seem to indicate that storing the CC-BY licensed code in a binary and distributing it would be applying an "Effective Technological Measure" that would prevent someone that receives said binary from exercising their right to view, modify, and distribute the CC-BY content contained in the binary. That does seem copyleft from a software perspective! – moorepants Jan 20 at 20:24
  • With MIT licensed code I believe that you can modify it and license the modified code as GPL as long as you include the original MIT license when distributing the modified code, but all downstream recipients of this GPL'd code would have to abide by the GPL (as well as the MIT). But this CC-BY clause seems to indicate that I could not GPL modified CC-BY code because it imposes different terms and conditions on the original code. So, this is problematic for distributing source code under more restrictive licenses, not just for binary distribution. – moorepants Jan 20 at 20:41
  • 3.a.4 says "If You Share Adapted Material You produce, the Adapter's License You apply must not prevent recipients of the Adapted Material from complying with this Public License." which also seems to imply a weak copyleft protection. – moorepants Jan 20 at 20:47
  • This answers the questions for my purposes. Thanks! – moorepants Jan 20 at 20:48

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