Dual License?
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Hey all,
I have a quick question. If something is dual licensed, is it considered "free"?
I think I have a decent understanding of the FSF guidelines, but FBreader stumps me because they have a default GPL license and a separate "closed-source" commercial license.
FB Reader - see the bottom of the page for licensing information
I was looking at this product since there has been a recent discussion about the possibility of a tablet, and this seemed like the perfect reader for a tablet.
As long as you have a GPL'd version, that version will always be free. The copyright holder does have the right to sell and/or distribute under alternative licenses. But that does not make the GPL'd version any less free.
One of my favorite JavaScript frameworks is jQuery and they are dual licensed with MIT and GPLv2: http://jquery.org/license/
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Dual license can mean different things depending on the circumstance. In this case (FBReader) it looks like they offer the GPL version to the public, with the option to buy a proprietary license that does not have the rules of the GPL attached to it. This is of interest only if you're a proprietary software developer, which you probably are not. There's plenty of projects that offer paid proprietary licenses, such as Qt. The version available to you is a GPLed version.
Another meaning of dual license simply means that the source is made publicly available under two licenses, and you are allowed to choose one to abide by. Mozilla software is often licensed under three licenses (GPL, LGPL, and MPL). jQuery and jQuery plugins tend to be dual licensed under the GPL and the MIT licenses, although I'm unclear what purpose that serves (as the MIT license is fully compatible with the GPL by default).
Maybe the reason jQuery offers MIT is how the GPL works. MIT is pretty much public domain so you can do whatever you want with it. GPL has strings attached and that's why some people have claimed that GPL code "infects" other code by forcing all of it under the GPL.
Let's take a look at this example with Apache 2.0 and GPLv3:
Apache 2 software can therefore be included in GPLv3 projects, because the GPLv3 license accepts our software into GPLv3 works. However, GPLv3 software cannot be included in Apache projects. The licenses are incompatible in one direction only, and it is a result of ASF's licensing philosophy and the GPLv3 authors' interpretation of copyright law.
This licensing incompatibility applies only when some Apache project software becomes a derivative work of some GPLv3 software, because then the Apache software would have to be distributed under GPLv3. This would be incompatible with ASF's requirement that all Apache software must be distributed under the Apache License 2.0.
We avoid GPLv3 software because merely linking to it is considered by the GPLv3 authors to create a derivative work. We want to honor their license. Unless GPLv3 licensors relax this interpretation of their own license regarding linking, our licensing philosophies are fundamentally incompatible. This is an identical issue for both GPLv2 and GPLv3.
The question is in the other way around: what would be the advantage for a user/developer to choose to receive the code under the GPL? If you choose the MIT license you can relicense the code under the GPL! So it looks to me that distributing the software under the MIT license only would not change anything.
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