[License-discuss] Strong and weak copyleft

[Ben Tilly]

I believe that the legal key is distribution of the licensed code, not
linking to it.

The LGPL defines a "Combined Work" and has requirements on what is
required when you distribute a combined work together.  The intent is
clearly that if you distribute the combined work together and DO NOT
meet those conditions, then you had no permission to distribute the
LGPLed code.  And this has force because while the proprietary half of
a combined work is not a derived work, you still need permission to
distribute some else's copyrighted code and that permission was
contingent on what you did with your application.

The GPL defines a covered work to be, "either the unmodified Program
or a work based on the Program."  Later in the license a distinction
is drawn between that and "mere aggregation".  The intent is that
distributing your program + the covered GPLed code it depends on
creates a work and you need GPL permission to have distributed the
covered GPLed code.  (Whether a judge will agree with this
interpretation is another question, but I'm pretty sure that the
license drafters intended a judge to understand it this way.)

With that said, the LGPL gives a lot of license flexibility for your
part of the combined work but says you must allow reverse engineering.
Which by default is allowed in many places, but is something that many
proprietary licenses take away.  By contrast the GPL offers no real
alternative but to license the code you own under the GPL.  Therefore
LGPLed code keeps itself copylefted but does not encourage developers
to GPL their own code.  While GPLed code pushes people who want to use
that code to have to GPL the code that they wrote.

On Tue, Apr 7, 2015 at 10:23 AM, Lawrence Rosen <lrosen at rosenlaw.com> wrote:
> Patrice-Emmanuel Schmitz referred me to this thought-provoking link:
>
>
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> https://joinup.ec.europa.eu/community/eupl/news/meaning-%E2%80%9Ccopyleft%E2%80%9D-eupl
>
>
>
> Can anyone here precisely identify the language in the GPL licenses that
> makes it "strong" rather than "weak" copyleft? And can anyone here identify
> anything in copyright law or cases that allow this distinction in the
> meaning of "derivative work"?
>
>
>
> /Larry
>
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>
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