GPLv3's secretive Additional Terms

[Luis Villa]

Two requests for clarification inline:

On Wed, Apr 21, 2010 at 2:55 PM, Chris Travers <chris at metatrontech.com> wrote:
> On Wed, Apr 21, 2010 at 1:27 PM, John Cowan <cowan at ccil.org> wrote:
>> opensource.*.nwo at neverbox.com scripsit:
>>
>>> GPLv3's possibly most secretive addition is section 7. Additional Terms.
>>> The GNU site and the online world in general pretend like it doesn't
>>> exist. I'm especially baffed by the statement "when you convey a copy of
>>> a covered work, you may at your option remove any additional permissions
>>> from that copy."
>>
>> The key to understanding 7 is to distinguish between additional
>> permissions and additional restrictions.  The first are things that you
>> want to allow that the GPL would not by itself allow; the second are
>> things that you want to forbid that the GPL would not by itself forbid.
>
> Unfortunately, there are a lot of things which aren't entirely black
> and white here.  IANAL, etc.
>
> For example, suppose I incorporate a BSD-licensed file into a GPL
> v3-licensed work.  Pretty much everyone agrees I can do this, or even
> if they don't they at least concede that this was a goal of the GPL
> v3.
>
> However, you run into a problem here trying to read the BSD license as
> basically the GPL v3 plus additional permissions.  In essence, I don't
> think you can simply chance the copyright on the otherwise-unchanged
> BSD-licensed file by invoking section 7 of the GPL v3 (and Richard
> Fontana from the SFLC has, in the past, opined as much on this list),
> but that relicensing restriction is not in line with the additional
> restrictions section either.

Which relicensing restriction are you referring to here?

> A very strict reading of section 7 of
> the GPL v3 would therefore render it incompatible with the BSD
> license.
>
> But this ends up creating a great deal of difficulty.  If the
> restriction that, absent significant changes, a file cannot be
> relicensed is an implied exception,

Implied exception to...?

> does that mean that I can include
> proprietary software libraries in closely tied ways, creating an
> implied additional restriction as well?  To be honest, even after a
> few years, I still don't have a principled way of reading this
> session.  I think the closest one could come to would be a
> "substantive interest" test where additional restrictions might be
> allowed if they didn't prejudice a substantive interest on the part of
> the licensor, such as source code availability, or the ability to
> refactor code.  This would allow open source licenses generally to be
> deemed compatible (perhaps to a much greater extent than the GPL v2--
> would the MPL be compatible?) but might stop short of limiting it to
> files used.
>
> I don't know though.  This (and the AGPL compatibility exception
> written in) are major reasons why I avoid releasing work under this
> license.
>
> I wouldn't call it secretive though.  Just that compatibility in
> licensing is a difficult thing and that there are some important
> shortcomings there.
>
> Best Wishes,
> Chris Travers
>