compatibility Re: License committee report for January 2008

Ben Tilly btilly at
Mon Jan 28 23:05:25 UTC 2008

On Jan 28, 2008 12:50 PM, Alexander Terekhov
<alexander.terekhov at> wrote:
> On Jan 28, 2008 9:33 PM, Ernest Prabhakar <ernest.prabhakar at> wrote:
> > Hi Alexander,
> >
> > > Really? And that would mean what, exactly?
> >
> > The short answer is that we all would like to see the fewest number of
> > incompatible licenses in the world.  The GPL/LGPL's incompatibility
> > with certain other licenses is accepted as a "fact of life" by most
> > open source developers, but that's no reason to encourage/enable
> > additional incompatibilities.
> >
> > Beyond, I'm afraid I've completely lost track of the argument.  It
> > would help if you could reframe your concern in the form of a Q & A,
> > so we can document any discussion in the FAQ.
> Q1) What does "compatibility" mean in the context of licensing?
> A1) Well, in the GNU Republic, it means ability to "relicense" under
> the GNU GPL. For example, the LGPL is "compatible" with the GNU GPL
> thanks to its GPL relicensing clause:

I like the question, but not the way you put the answer.  Here are a
series of questions and answers on this topic.


Q1) What does "compatibility" mean in the context of licensing?

A1) Two licenses are compatible if their terms allow you to create,
modify and distribute software that includes code under each license.
In general permissive licenses tend to be compatible with other
licenses and restrictive ones do not.  For example it is easier to
include code under the MIT in other projects than it is to include
code that is licensed under the GPL v2 or later.

Q2) Can I freely include code in my project that is under a compatible license?

A2) No.  Compatibility just means that you can create code that
derives from both.  However the combined result must respect both sets
of copyright terms.  Therefore including code under another license
may require you to change your own license terms.

In general projects that use a permissive license (such as the MIT
license) need to be careful when including code, but their code can be
widely reused, while projects that use a restrictive license (such as
the GPL) can use code from other projects but their code cannot be
reused as widely.  This directionality can be a source of conflict
between different developers and projects.

Q3) What is GPL compatibility?

A3) An important special case of license compatibility is
compatibility between the GPL v2 or v3 and anything else.  Given the
GPL's restrictions on sublicensing, it is usually only compatible with
another license when code under the other license can be relicensed
under the GPL.

The OSI does not issue opinions on the compatibility of particular
pairs of licenses.  However the Free Software Foundation does issue
opinions on whether specific licenses are GPL compatible.  Their
licensing page is at


The key goal that I had in phrasing that was to be accurate, fair and
impartial while not hiding potentially divisive issues.


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