BSD and MIT license "compliance" with the MS-PL

Matthew Flaschen matthew.flaschen at
Sat Apr 18 21:33:00 UTC 2009

Tzeng, Nigel H. wrote:
>> From: Matthew Flaschen [matthew.flaschen at]
>> Because in this case, I think the FSF (or rather the one unknown
>> but well-intentioned person who updated that license list) is
>> contradicting their own definition (
> Except their definition does not define weak copyleft explicitly.

No they don't.  But it's obviously a type of copyleft.

>> Weak copyleft is no excuse for a weak definition.
> The defining aspect of all copyleft licenses, weak or strong, is that
> they are one way licenses (aka viral). 

That definition does not match historical usage of 'copyleft', in my
> Given that the MS-PL is an open source license (OSI) and a free
> software license (FSF) and it's viral  it's hard to argue that it
> doesn't preserve source availability and therefore doesn't qualify as
> a weak copyleft.

Actually, it's quite easy to argue that it doesn't preserve source
availability.  A distributes alpha version of Foo under MS-PL.  B makes
FooBar derivative, which becomes fanatically popular, and no version of
FooBar's source is ever released.  Source availability is denied for
almost every user of a Foo derivative.

Matt Flaschen

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