support requirement

[Seth David Schoen]

VAB writes:

> [...] I've been 
> wondering about dual licensing for some time now.  The example that
> brought it to my attention was the PHP licensing.  PHP consists of
> an interpreted programming languages (much like perl), and a run time
> for that interpreter.  When you download PHP from www.php.net you are
> allowed to choose between the GPL and a less restrictive license
> written by the PHP programmers which allows commercial forking.  What
> position does this put the PHP programmers in?  Are they allowed
> to pick up code from the community (GPL'd code) and include it in
> PHP from which it can then propagate to commercial forks of PHP?

No.

The idea is that the copyright law ordinarily prohibits people to do
certain things, but licenses allow them to do these things.

If the copyright owner grants you a particular license, you may then do
the things which the license allows.  This is true regardless of what other
licenses have been granted to you or to other people.

Nobody is allowed to grant licenses to other people's code.  (The GPL alludes
to this when it says "Thus, it is not the intent of this section to claim
rights or contest your rights to work written entirely by you; rather, the
intent is to exercise the right to control the distribution of derivative or
collective works based on the Program.")  Issuing a program under one license
never precludes you from issuing it under other licenses in the future, but
this doesn't mean that you may ever issue other people's code under arbitrary
licenses.

> I've seen many other people do dual licensing with supposedly "GPL"
> compatible licenses such as the artistic license as well.

They are allowed to do that, if they are the authors.  If they want to do
that with other people's contributions, and those contributions were not
also explicitly dual-licensed, they need to check with the contributors
before dual-licensing the contributions.

> Am I mistaken and this type of dual licensing is only possible 
> with an original work which contains no previously GPL'd code?

It is only possible if all of the authors of the work have consented to it.
Whether or not the authors have issued their work under the GPL in the past
has nothing at all to do with whether it may be re-issued under other
licenses.

> I had thought that this would be the case based on my reading 
> of the GPL, but I have a hard time believing that all of the
> code dual licensed out there is original code.  Will it satisfy
> the GPL's viral clause (Paragraph 2b) to have the code licensed
> by multiple licenses and at least one of those licenses be the
> GPL?

Yes, certainly.  (Remember that "it is not the intent of this section to
claim rights or contest your rights to work written entirely by you".)
But it will not satisfy _copyright_ to have the code licensed by multiple
licenses without the consent of the copyright holders.

> Is there a way I can prevent this from happening to my software?
> Is it legally possible for me to write a license that restricts
> any one at any time in the future from dual licensing any of the
> code that I write and taking it away from the community?

The GPL will do that.

-- 
                    Seth David Schoen <schoen at loyalty.org>
      They said look at the light we're giving you,  /  And the darkness
      that we're saving you from.   -- Dar Williams, "The Great Unknown"
  http://ishmael.geecs.org/~sigma/  (personal)  http://www.loyalty.org/  (CAF)