jQuery, jQuery UI, and Dual Licensed Plugins (Dual Licensing)

Question

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
*/

Answer 1

I'm also not a layer, but I think the AND/OR just depends on point of view. The code is licensed under both licenses (AND), while you can use it under term of either license (OR).

Answer 2

GPL explicitly forbids adding additional restrictions, so the only valid form of dual-licensing is to allow users to use it according to the GPL licence OR use it according to the MIT license (which is what dual-licensing means, anyway).

Answer 3

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 (e.g. 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.

Answer 4

IANAL and you shouldn't get legal advice from a website. But in my opinion there are only two possible reasons to care about licensing:

1. You want to use the code. You need the copyright holder's permission, and thus you must use it under whatever license the copyright holder(s) gives you. In this case you get to choose because it is dual-licensed. It is a logical contradiction to license the software simultaneously under both licenses at the same time because the GPL adds requirements that the MIT license does not. Therefore you as the user can choose one OR the other. Note: if you are distributing the code you can presumably carry-forward the dual-licensing too if your own project is dual-licensed accordingly. But if you want to operate under the terms of just one license you can.

2. You want to contribute to the code. In that case you need to know that your code will also be dual-licensed. For example, it is generally impossible to contribute to the Linux kernel any code that isn't GPLv2. And if you ONLY want to contribute GPL code (because you are a strong believer in copyleft) then you must be aware that jQuery is GPL AND MIT, which means your code must be similarly GPL and MIT.

Answer 5

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