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

Tzeng, Nigel H. Nigel.Tzeng at
Sat Apr 18 11:35:03 UTC 2009

>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.

>> My definition of strong copyleft is the same as yours.  My definition
>> of "weak" copyleft is "something less than strong copyleft" and
>> fuzzier because weak copylefts are "weaker" than strong copylefts in
>> different ways.

>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).  Meaning you can combine them with other works or make derivatives but the resulting work is covered by the original copyleft license.  In the context of software copyleft licenses, the minimum criteria for weak copyleft is that they be open source and viral.

All copyleft licenses are annoying because they all build walls in what they claim to be a "commons".  We put up with them because they serve specific purposes:  prevents others to use in their own proprietary products, always allows others to use in their own proprietary products, whatever.

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.

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