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Suppose I receive a copy of some software with the BSD 2-Clause Plus Patent license. Can I make some modifications to that software, then distribute my changed version of that software under the BSD 2-Clause "Simplified" license?

Conversely, if I receive some software under BSD-2-Clause, can I modify it and distribute the modified version under BSD-2-Clause-Patent?

The reason I am not sure, is because while both of these licenses contain a clause requiring me to "retain this list of conditions", the patent grant section does not appear to be a "condition" in the same sense as the other conditions, and it does not appear in the "list" if one considers the scope of the list to consist only of the numbered paragraphs. So it seems to allow the possibility of dropping the paragraph section (or adding it when it is not present) without otherwise going against the terms of the license.

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I'm not sure about removing it, not least because I'm not sure why you would, but you definitely shouldn't add it if it's not there in what you got from upstream. This is because the patent clause says that "each copyright holder and contributor hereby grants to those receiving rights under this license a perpetual [...] patent license".

Since you've received no such licence for any patents that might be embodied in the code you got from upstream, you're in no position to promise that such a licence exists. I don't know how false a position you'd place yourself in by adding such a promise - I suspect it's jurisdictionally-dependent - but nothing good can come of it.

BSD-style licences aren't copyleft, so there's no reason to have the whole codebase under a single licence, and certainly not a single BSD-style licence. If you're minded to use BSD2-plus-patent-clause for the code you add, that's great, feel free to do so; but leave the upstream stuff under plain BSD2.

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  • It should be added that the use of the BSD-2-Clause Plus Patent License only helps downstream recipients, if the contributor actually owns a relevant patent. If you don't own a patent it makes absolutely no difference for downstream recipients, it might even give a false sense of comfort. Jan 22 at 16:20
  • Agreed, but in adding it the OP would still give downstream reason to believe that someone had made such a grant, whether useful or not, when they in fact had not.
    – MadHatter
    Jan 22 at 16:25
  • Agreed, adding it for existing code is a big no-no, as you explained in your answer. Jan 22 at 17:39
  • @Martin_in_AUT I don't really see why not holding a relevant patent is a reason not to add the patent clause (assuming I'm the only author or can otherwise attest to what patents are held by the contributors to the code), but that's a different question than this one so I'll ask it seperately. Jan 23 at 17:38
  • @ChrisPressey For downstream users of your code there is no benefit whatsoever to know that 1 contributor without a relevant patent out of a world population of 8,000,000,000 people states that (s)he is licensing all of these non-existent patent rights to downstream users. There are still 7,999,999,999 others left who might hold a relevant patent, and in addition a lot of companies which own the majority of patents world-wide. Jan 24 at 7:56

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