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From https://choosealicense.com/licenses/ and https://choosealicense.com/appendix/ I notice that the MIT license doesn't have "patent use" permisson like other popular open source licenses.

What does it indicate? What's the difference?

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The MIT and BSD licenses were drafted before software patents were common. Therefore, they completely ignore the topic. For users of MIT- or BSD-licensed software, this creates the risk of a kind of submarine patents. A rights holder could release software involving patented technology under such an open-source license, and later try to sue users for their patent violation.

This absence of any mentions of patents has been construed by some as an implicit patent license. If someone releases software to the public, then surely they must have intended for that software to be used by the public, despite any patents? Although not completely unreasonable, that is a rather shaky argument. Some kinds of implied patent licenses have been upheld by U.S. courts. However, that observation ignores that open source is a global phenomenon, and most users (including myself) are not under the jurisdictions of U.S. courts.

Some projects have clarified the MIT and BSD licenses with an explicit patent grant. For example, React from Facebook used to be licensed under the BSD + a separate patent license between 2014 and 2017. The terms of this patent grant disproportionally favoured Facebook over users and made the combined license incompatible with many other open source licenses. After a few rounds of user outcries, they relicensed under a standard MIT license, without any explicit patent grant.

The Apache 2.0 License (and later the GPL 3) introduced an explicit patent grant to the user that only terminates if that user starts any patent litigation that claims that the licensed work were infringing. This approach improves clarity through an explicit patent grant and deters patent trolling, thus protecting other contributors and users. In my opinion, this makes the Apache 2.0 license vastly preferable to licenses like ISC, MIT, or BSD variants that ignore patents.

  • So what you are saying is MIT is like: Use the code however you want but when you fork it we may sue you... That is essentially on purpose misleading. – Ini Jan 6 at 14:06
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    @Ini Part of the problem here is that an open source license should be valid in all jurisdictions, which differ in whether implied or non-express licenses can even exist. That "without restriction" part is seen by some as an express patent license even though the word patent isn't mentioned. There is also an argument based on the estoppel concept in common law. Modern licenses tend to avoid these problems and include an explicit patent grant; where MIT/BSD style licenses are used by entities with many patents you might see them amend the license with a clarification. – amon Jan 6 at 14:10
  • But you only have to care about the laws of the juristriction where you live in, right? – Ini Jan 6 at 18:02
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    @Ini Yes, the license must first be legal in the author's jurisdiction. But I want the software that I write in Germany to be legally usable in the US, Quebec, China, and elsewhere. So I should use a license that is valid in all of these jurisdictions. That is really tricky but thanks to the Berne convention and WIPO there's at least some agreement about the concept of copyright. So most open source licenses derive their enforceability from copyright law (which is internationally harmonized) and not from contract law (which differs wildly between jurisdictions). – amon Jan 6 at 18:16
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    One specific problematic area is the public domain. In the US works can be actively placed in the PD. In Germany, works can only land in the PD if the copyright term expires. That means I am legally unable to contribute to PD-"licensed" projects! If I were to modify such a project, I'd have to instead use a fallback license that is functionally equivalent to a PD dedication (e.g. CC0). – amon Jan 6 at 18:19
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According to RedHat, who happens to be a prominent participant in FOSS IP litigation, the clauses to deal in the Software without restriction and including without limitation already expressly grants patent rights, at least under US law.

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