Convert GPL to MPL

John Cowan cowan at
Fri Jan 18 18:21:16 UTC 2008

Arnoud Engelfriet scripsit:

> Marcel Ferrante wrote:
> > If a open source uses GPL License and I do a fork and do many
> > modifications, I can change its license to MPL, to turn the software
> > a commercial open source ?
> No, you can't do that. Only the copyright holders, usually the authors
> of the GPL software, can change the license. This is a standard feature
> of copyright law.

I think the answer "no" is correct (pace Larry), but the explanation is
subtly misleading.

If Alice issues a work A and licenses Bob to make a derivative work
B, then Bob is the owner of B and can, in the general case, license
it however he wants.  Bob is not the owner of A and can't license it,
or copies of it, except as Alice allows.  For example, if A is a novel
and B is the film made from it, Alice has no say in Bob's distribution
arrangements, unless some agreement exists restricting Bob in this way.
Furthermore, Bob cannot in general prevent Charlie from making his own
work C, another derivative of A, under a license from Alice.

In the case where A is licensed under the GPL, however, Alice has said:
"All derivative works of A, whether created by Tom, Dick, or Harry, must
be licensed by them under the GPL and only the GPL."  So an MPL-licensed
derivative has been explicitly forbidden by Alice.


John Cowan      <cowan at>
                Charles li reis, nostre emperesdre magnes,
                Set anz totz pleinz ad ested in Espagnes.

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