[ProgSoc] GPL and license compatibility

John Elliot jj5 at jj5.net
Wed Aug 24 09:17:53 EST 2011

On 16/08/2011 7:37 AM, Nicholas FitzRoy-Dale wrote:
> On 15/08/2011, at 1:14 PM, John Elliot wrote:
>> I've noticed that some projects will dual license their content under the GPL *and* some other more liberal license such as the MIT or *BSD licenses.
>> Is this necessary?
> Depends what for...

I'm still not clear on when this becomes necessary. If the BSD and MIT 
licenses are compatible with the GPL, why license under the GPL too? I 
don't understand...

>> If I'm working on a GPL licensed project and I want to use a library that is licensed under a MIT or *BSD license, can I do that? Or do the libraries that I'm referencing need to be also licensed under the GPL (or LGPL) too?
> No, in this case you can just include MIT or BSD licensed libraries, as they are generally considered to be "compatible with the GPL".
> Here is the FSF on what that means: http://www.gnu.org/licenses/gpl-faq.html#WhatDoesCompatMean

Thanks, I found these too, which were helpful:

* http://www.gnu.org/licenses/license-list.html
* http://en.wikipedia.org/wiki/List_of_FSF_approved_software_licenses

> The MIT and BSD licenses aren't strict subsets of the GPL, which is why some projects choose dual licensing.

I don't understand why that is important, given that they are compatible.

> Here is Theo de Raadt on it: http://undeadly.org/cgi?action=article&sid=20070901041657

Man, that guy strikes me as a tedious prat. It would seem pretty clear 
to me that if a project is "dual licensed" that the copyright holders 
are allowing you to have the project under one license *or* the other. 
Creating new documentation in your fork that explains which license you 
have elected to apply isn't "modifying" their "legal documents" in any 
way that you haven't been implicitly authorised to do so. Coming up with 
an interpretation that suggests otherwise is lame, pedantic and 
bordering on pathetic I reckon. Trying to put the fear of "the law" in 
people with a contrived interpretation... bah!

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