For Approval: Microsoft Permissive License

Philip Hunt cabalamat at
Sun Aug 19 12:11:09 UTC 2007

On 8/19/07, Chris Travers <chris at> wrote:
> I don't think the question of whether Microsoft incorporated these terms
> because they are incompatible with the GPL v2 (which requires that you
> *guarantee* patent licenses downstream possibly through an action
> separate from the license, and there is no procedure for revoking them
> if patent suits are filed) is the issue.

I agree, I don't think it's the issue either. However I do think some
similar questions are valid.

Consider someone who is proposing a new open source license. For their
proposal to make sense, they should consider other common open source
licenses. They should do this for at least two reasons: (1) to see if their
proposal adds anything new and is not too similar to an existing license,
and (2) to consider whether they intend for their proposed license to be
compatible with other common licenses.

They should do the 2nd not just for the reason that compatibility is,
other things being equal, a desirable goal, but also so that they can be
clear about what their license intends. For example, a proponent might
intend their license to be GPL-compatible, but it is not; or they might
intend it to be incompatible, but it is.

Finding out what the proponent intends of their license is a necessary
step in checking that the license actually does what people think it does.

(Note in the above I do not want to give the impression that I think
a license is necessarily undesirable because it is incompatible with
another license; a license can be incompatible with others and still be

So, what licenses should a proponent consider when proposing a new one?
I would suggest at the very least the GPLv2 and the MIT license. Ideally
they should consider all the ones labelled "Licenses that are popular and
widely used or with strong communities" on

So in the spirit of the above, I would like to ask Jon Rosenberg:

Is the MS-PL intended to be compatible with the MIT license?
Is the MS-PL intended to be compatible with the GPLv2?
Is the MS-PL intended to be compatible with the GPLv3?

> Whether Microsoft intended these to be incompatible with the GPL v2 and
> compatible with the Apache License 2.0 would not be an issue except in
> some peoples minds.

The GPLv2 is by far the most common open source license in use today (it's
used by 65% of all projects on Freshmeat). If a proponent of a license hasn't
asked themself the question "should my license be compatible with the GPL?"
and come to a firm answer, then I would suggest they need to think more about
the issue and come back when they have done so.

Philip Hunt, cabalamat at

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