When to evaluate dual licenses (was: license categories, was: I'm not supposed to use the ECL v2?)

[Ben Tilly]

On Dec 3, 2007 1:06 AM, Wilson, Andrew <andrew.wilson at intel.com> wrote:
> Chris Travers wrote:
> >On Dec 2, 2007 6:22 PM, John Cowan <cowan at ccil.org> wrote:
> >       Lawrence Rosen scripsit:
> >
> >
> >       > I don't believe that. If my choice is between License A and
> License B, I
> >       > can't pick and choose some combination of provisions from A
> and B to create
> >       > my own preferred set of terms. I get either A or B, but not
> both.
> >
> >
> >       Well, in that case how is it possible, given a work issued under
> the GPLv2
> >       or later, to issue a derivative work which is still under GPLv2
> or later?
> >       Clearly the derivator is not making a choice here.
> >
> >
> > I am not sure what you mean by that.  If you take your work and
> license it under the GPL v2 or later, I can make a derivative work
> > and choose any of the following licensing choices:
> > 1)  GPL v2 only.
> > 2)  GPL v3 only.
> > 3)  GPL v2 or later.
> > 4)  GPL v3 or later.
>
> This is a very interesting question.  Let's assume, for purpose of
> discussion, that
> it is axiomatic that the license of a derivative work of GPL code ==
> effective license of the
> original GPL code.  {Yes, I know, not everyone accepts this.  Stop
> reading now
> if you don't.}

I have a sneaking suspicion that I've just been asked to stop reading.
 But I have to ask.  Why would this be axiomatic?

[...]
> So, back to "GPLv2 or any later."  Post July 2007, this amounts to a
> dual license
> GPLv2/GPLv3.  So, for original code licensed in under "GPLv2 or any
> later", there are
> three possible answers for the effective license which applies to code
> licensed out:
>
> 1) GPLv2 only  (original license evaluated and constrained to v2)
> 2) GPLv3 only  (original license evaluated and constrained to v3)
> 3) GPLv2 or any later ("lazy evaluation": original license passsed
> through
> and ultimate choice of license deferred to downstream distributees)
>
> If you accept, again, that the license out of a derivative work of GPL
> code must
> be equivalent to the effective license in of the base code, then Chris's
> cases 1-3 are covered.
> I'm not sure how you get to Chris's case (4) -- licensing out a
> derivative of "GPLv2 or later"
> as "GPLv3 or later."

My theory is that you accept the licensed code under GPL v3 and
release your modifications as GPL v3 or later.  That makes the license
on the combined work be the intersection of the original (GPL v2 or
later) and your code (GPL v3 or later) which is GPL v3 or later.

Can you do that?  Well look at section 5 c of the GPL v3.  It requires
your derivative work to be licensed under the GPL v3.  But it says
nothing to stop you from giving additional permissions.  And it
explicitly says, "This License gives no permission to license the work
in any other way, but it does not invalidate such permission if you
have separately received it."  Since you received it with the "...or
later" language then you have additional permissions, they are valid,
and nothing stops you from granting similar ones to other people.

In other words the GPL v3 makes it clear that accepting the code under
the GPL v3 license does not invalidate the permissions you get from
all other licenses that may apply to the code.  (Even though they are
not yet written!)

Cheers,
Ben