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CC0 is often criticized for its patent clause

No trademark or patent rights held by Affirmer are waived, abandoned, surrendered, licensed or otherwise affected by this document.

At the same time, many other licenses (e.g. BSD, MIT) don't even mention patents, so presumably, they have the same weakness.

For example, presumably, I can hold a patent for an algorithm, and distribute its implementation with a short permissive license like BSD. I can't see in the BSD text any conflicts with that.

So, why CC0 is criticized for its explicit patent clause, and not approved by OSI, whereas short permissive licenses like BSD, MIT, ISC, etc. are not?

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BSD and MIT don't mention patents, but have language that can be reasonably interpreted as an implied patent license. You can't use, publish, distribute, and/or sell software and deal with it without restriction if the rightsholder hasn't given you the necessary rights. The necessary rights include copyrights and patent rights. Note that the MIT license doesn't explicitly mention copyright either!

CC0 explicitly says that it doesn't include any patent license, so there is no scope to argue for an implied patent license. The result is that a patent-encumbered software that is otherwise in the public domain per the CC0 device cannot be used, shared, and modified freely. Such terms fail to provide Software Freedom, so CC0 cannot be approved as Open Source. If the CC0 had been silent on the matter of patents or would have at least included a minimal patent license, then CC0-covered software would clearly be Open Source.

The unfortunate result is that there's no good tool to release software into the public domain in a manner that ensures Software Freedom. The CC0 is excellent except for its exclusion of a patent license. While the Unlicense has been legacy-approved by the OSI in the meanwhile, it's a pretty shoddy license, doesn't mention patents, and might not actually work as a public-domain equivalent grant in many jurisdictions.

Note that this isn't a design flaw of the CC0 device. It's great at its job of releasing copyright and related rights into the public domain to the fullest extent possible under applicable law. If a rightsholder also wanted to release their patent rights they could use a separate but similar device. But there's a fundamental difference between copyright and patents: whereas copyright is automatic and must therefore be explicitly released, patents are only granted upon request. If someone goes through the trouble of securing a patent, it's unlikely that they would then want to publicly release all their rights.

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  • BSD implementations of patented algorithms are released all the time. I don't see how an oversight by a developer can grant any patent license. Sep 30, 2022 at 17:59
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    @StefanvanderWalt If the patent-holder releases their code under an Open Source license it's clear they are intending people to use and modify that software, so that it might be reasonable to consider this an implied patent license. If someone other than the patent holder releases that code, they can't grant a license to rights that they don't hold. It doesn't matter whether they use BSD or Apache, there will not be a license to relevant patents attached. For example, I don't hold any patents. Ergo, no software that I released caused any patents to be licensed.
    – amon
    Sep 30, 2022 at 19:46
  • That makes sense, thank you for the clarification. Oct 1, 2022 at 22:34
  • What's the threat model here, anyway? Is it something like: X publishes codebase libA as CC0, but libA (whether actually, or via some tortured legal argument) implements some patent held by X, so later on when CorpY has deployed libA in production, X might then contact CorpY and say “Surprise! You're infringing on our patent rights with libA, which you thought we'd published freely into the world given its CC0 status! You must either pay us a patent license; or rebuild your application(s) without libA; or face a lawsuit!” Nov 3, 2023 at 13:37
  • @JamesTheAwesomeDude Yes, that is a concern. Keyword: "submarine patents". But irrespective of the likelihood of such a scenario, it demonstrates that a copyright license alone cannot provide Software Freedom when there are unlicensed patents. A high-profile example of controversy about patent licensing in Open Source projects was the React license from 2014 to '15 and in less problematic form until 2017. During that time, React included an explicit patent license, but with terms that disproportionately favored Facebook (now Meta).
    – amon
    Nov 4, 2023 at 15:09

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