jQuery, jQuery UI, and Dual Licensed Plugins (Dual Licensing)
OK I have read many posts regarding Dual Licensing using MIT and GPL licenses. But Im curious still, as the wording seems to be inclusive. Many of the Dual Licenses state that the software is licensed using "MIT AND GPL". The "AND" is what confuses me.
It seems to me that the word "AND" in the terms, means you will be licensing the product using both licenses. Most of the posts, here on stackoverflow, state that you can license the software using one "OR" the other.
JQuery specifically states "OR", whereas JQuery UI specifically States "AND". Another Instance of the "AND" would be JQGrid.
Im not a lawyer but, it seems to me that a legal interpretation of this would state that use of the software would mean that your using the software under both licenses. Has anyone who has contacted a lawyer gotten clarification or a definitive answer as to what is true? Can you use Dual licensed software products that state "AND" in the terms of agreement under either license?
EDITED: Guys here is specifically what Im talking about on jquery.org/license you see the following stated:
You may use any jQuery project under the terms of either the MIT License or the GNU General Public License (GPL) Version 2
but in the header of Jquery's and Jquery UI library you see this:
* Dual licensed under the MIT and GPL licenses.
* http://docs.jquery.com/License
The site says
MIT or GPL
but the license statement in the software says
MIT and GPL.
UPDATE May 7, 2010 There is clearly something to this question as JQuery has changed the wording of thier licence agreement in thier latest release to state MIT OR GPL.
Release 1.3.2 license says:
/*
* jQuery JavaScript Library v1.3.2
* http://jquery.com/
*
* Copyright (c) 2009 John Resig
* Dual licensed under the MIT and GPL licenses.
* http://docs.jquery.com/License
*
* Date: 2009-02-19 17:34:21 -0500 (Thu, 19 Feb 2009)
* Revision: 6246
*/
But now Release 1.4.2 license says:
/*!
* jQuery JavaScript Library v1.4.2
* http://jquery.com/
*
* Copyright 2010, John Resig
* Dual licensed under the MIT or GPL Version 2 licenses.
* http://jquery.org/license
*/
John Resig owns the copyrights to the code and he can license it to anybody he wants and under any terms he wants within the constraints of copyright law.
He has chosen to license the code under GPLv2, perhaps because he wants to encourage the producers of other GPL licenced products to use this software.
He has also chosen to license the code under the MIT license, perhaps because he wants to encourage producers of open-source and proprietary code to use this software.
If you read over the licenses, a piece of software cannot be GPL and MIT at the same time. GPL requires that distributors of derivative works distribute the entire source code of the entire derived work. MIT allows distributors of derivative works to withhold the source code. This is logically impossible. I suspect that when he dual-licensed the software, he meant that the two licenses were GPL and MIT. More specifically he did not say that the license (singular) is GPL and MIT.
Remember that you are the owner of the copyrights of any derivative works (eg applications that use/modify the open source software plus your own software). If derived your software from anything that is licensed under the GPL, you only had that right to make the derivative work if you agreed to license your derivative work under the GPL to anybody to whom you distribute the derivative work).
If you derived your application from MIT-licensed software then you are the copyright owner and you can license your application under any terms you want, including the exchange of money for a right to use the application. Apple Computer does that with their FreeBSD operating system base (licensed under a MIT-like license), and their proprietary Mac OS-X code on top.
Therefore, you should pick the license that suits your project and go with it. Usually it is more prudent to use the MIT license if you are a business that sells software but would like to keep the source code written by you secret. You will do better to pick GPL if you would like to ensure that the code base of your application remains liberated for anybody to study, use, and modify.
Having said that, you can still mix GPL code with MIT code without violating the terms of either license. The Linux folks do it all of the time with the kernel (GPL) and linked device drivers (GPL, MIT and some others). However, if you distribute the application, you must distribute the code base of the entire derived work including the GPL licensed software and the MIT licensed software, and you must license it to your customers under the GPL.
Check out my page at Squidoo for more insight.
I've updated the copyright for all jQuery UI source files to match the wording from jQuery core. http://github.com/jquery/jquery-ui/commit/536ae6189bf0f0de1113bf9ec7054da693544e1f
GPL明确禁止增加额外的限制，所以双重授权的唯一有效形式是允许用户根据GPL许可使用它，或根据MIT许可使用它（这是双重许可手段，无论如何）。
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