license-mix, legal consequences?

[Karsten M. Self]

on Sun, Jun 17, 2001 at 08:38:55AM -0300, Henningsen (alg at glinx.com) wrote:
> I want to release code I write myself under a dual license scheme,
> both GPL and commercial license, the latter for people who want to use
> the code in closed source projects. In my project I would like to
> include code released under the Tcl/Tk license model ("keep copyright
> notices in place, and keep this license text with the code"), and code
> released under the MIT license. 
> 
> I checked on the FSF's site whether these licenses are compatible with
> the GPL, and didn't find anything. Are they or are they not? And if
> they're not, would that mean that people who want to use my
> GPL-released code could not also use the code modules with
> incompatible licenses unless they got a special permission from me (in
> effect a free commercial license)?

Peter:

First, IANAL.

Dual licensing of your own code doesn't (generally) require
"compatibility" between licenses, defined as the ability for software
under one license to be used under the terms of another.  

This is effectively a logical OR:  compatibility requires that,
excepting other arrangements with the copyright holder(s), you can use
alternative or additional licensing terms.  This is a small set of
licenses.

Dual (or multiple) licensing, on the other hand, is a logical AND.
You're saying that any of the specified licenses is sufficient to meet
the legal obligations for software copying, modification, distribution,
or other 17 USC (or Berne, internationally) exclusive rights under
copyright.  

The issue that may then arise is the introduction of third-party code
into your project.  So long as this code is introduced under the same
dual/multi license terms, there are no compatibility issues raised.
However, if code is contributed under only one, or some other subset, of
licenses, the codebase as a whole becomes restricted as to which
portions can be used under what terms under altnernative licensing
arrangements.

As an example, I do work under Python.  Until now, Python has been
licensed under terms similar to the BSD/MIT license.  Last week, Guido
van Rossum announced that license compatibility with the GNU GPL had
been achieved.  I would prefer to license my own code under the
GPL/LGPL, and preferably no other terms.  This could create a conflict
for those who are using Python in, say, proprietary applications, but
would then have to determine whether or not they could incorporate code
authored by me, and/or under what terms.

Multiple licensing is an interesting hack, but it's not without its own
set of additional issues as well.

In your own case, my general understanding is that the MIT and Tcl/Tk
licenses should be compatible. 

I'd be interested in other viewpoints on this.

-- 
Karsten M. Self <kmself at ix.netcom.com>    http://kmself.home.netcom.com/
 What part of "Gestalt" don't you understand?       There is no K5 cabal
  http://gestalt-system.sourceforge.net/         http://www.kuro5hin.org
   Are these opinions my employer's?  Hah!  I don't believe them myself!
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