Dual licensing with two copyleft licenses

[Evan Prodromou]

On Thu, 2004-02-12 at 23:15 -0800, Brian Behlendorf wrote:

> "Only" - but for that work.  As I understand dual-licensing, as the author 
> distributed their work to you, you (the recipient) get to decide which 
> license applies to that action.  Perhaps that "only" applies only to the 
> copy you decided to apply the ShareAlike license to.  If you downloaded it 
> a second time, say, and said "this second copy was distributed to me under 
> the GFDL", then presumably the ShareAlike license doesn't apply to that 
> second copy.

I don't think copyright operates that way. I think, in the world of
copyright, those two copies you downloaded are the same work.

> Then the question is, can you take the same modifications 
> you made to the first copy and apply them to the second?  Since you are 
> the copyright owner of the modification, I assume you can - it's the 
> combination of the original and your modification that creates the 
> modified work that the ShareAlike or GFDL applies to, but not the original 
> modification.

Again, I think it takes some real sophistry to hold that the modified
version is really two separate works.

> Seems more definite to me; and it passes the gut-check too, as it also 
> seems unlikely that any author publishing under two licenses would intend 
> to only allow derivative works under only one license.

As far as gut check goes: I agree completely. I think most authors who
dual-license their work would want that derived works be available under
license A, license B, or both.

However, most licenses aren't created with dual-licensing in mind (the
MPL being a noteworthy exception). They're designed to be monolithic,
and when you mix-and-match them, you don't always get the results you
expected.

I think the upshot is: if you're writing a copyleft license (or
modifying an existing one), consider weakening the "absolutely precisely
definitely only this License and no other never" provisions to make it
more dual-licensing friendly -- "at least this License with no extra
restrictions", as in the GPL, seems like a good balance.

And if you're dual-licensing a work, check carefully for "only this
License" language, and make a written exception (like the one John Cowan
drafted earlier in this thread) if it's in one or the other or both
licenses.

~ESP

-- 
Evan Prodromou                  .O.
http://bad.dynu.ca/~evan/       ..O
evan at bad.dynu.ca                OOO