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.
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).
jQuery is no longer dual licensed. jQuery projects are now only distributed under the MIT license, which is GPL compatible. The majority copyright is now held by jQuery Foundation as all team members have signed a Copyright Assignment Agreement. Non-team members are now required to sign a Contributor License Agreement, but they still retain copyright of their contributions, just as they did before. We have updated all projects to include an AUTHORS.txt file listing all contributors. You can read more about this in a recent blog post.
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).
您想要使用代码。您需要版权所有者的许可，因此您必须根据版权所有者授予您的任何许可使用它。在这种情况下，您可以选择，因为它是双重许可的。同时在两个许可证下同时许可软件是一个逻辑矛盾，因为 GPL 增加了 MIT 许可证没有的要求。因此，作为用户，您可以选择其中之一。注意：如果您要分发代码，如果您自己的项目相应地获得了双重许可，那么您大概也可以继承双重许可。但是，如果您只想根据一个许可证的条款进行操作，则可以。
您想为代码做出贡献。在这种情况下，您需要知道您的代码也将获得双重许可。例如，通常不可能向 Linux 内核贡献任何非 GPLv2 的代码。如果您只想贡献 GPL 代码（因为您是 Copyleft 的坚定信徒），那么您必须意识到 jQuery 是 GPL AND MIT，这意味着您的代码必须类似 GPL 和 MIT。< /p>
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:
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.
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.
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John Resig 拥有该代码的版权，他可以在版权法的限制内按照他想要的任何条款将其许可给任何他想要的人。
他选择在 GPLv2 下许可代码，也许是因为他想鼓励其他 GPL 许可产品的生产者使用该软件。
他还选择根据麻省理工学院的许可证来许可代码，也许是因为他想鼓励开源和专有代码的生产者使用该软件。
如果你仔细阅读许可证，就会发现一个软件不能同时是 GPL 和 MIT 的。 GPL 要求衍生作品的分发者分发整个衍生作品的全部源代码。麻省理工学院允许衍生作品的发行商保留源代码。这在逻辑上是不可能的。我怀疑当他对该软件进行双重许可时，他的意思是这两个许可证是 GPL 和 MIT。更具体地说，他没有说许可证（单数）是 GPL 和 MIT。
请记住，您是任何衍生作品（例如使用/修改开源软件以及您自己的软件的应用程序）的版权所有者。如果您的软件源自根据 GPL 许可的任何内容，则只有当您同意根据 GPL 将您的衍生作品许可给您向其分发衍生作品的任何人时，您才有权制作衍生作品。
如果您的应用程序源自 MIT 许可的软件，那么您就是版权所有者，并且您可以根据您想要的任何条款许可您的应用程序，包括用金钱换取应用程序的使用权。 Apple Computer 通过他们的 FreeBSD 操作系统基础（根据类似 MIT 的许可）以及其专有的 Mac OS-X 代码来实现这一点。
因此，您应该选择适合您的项目的许可证并使用它。如果您是一家销售软件但希望对您编写的源代码保密的企业，通常更谨慎的做法是使用 MIT 许可证。如果您想确保您的应用程序的代码库仍然可供任何人学习、使用和修改，那么您最好选择 GPL。
话虽如此，您仍然可以将 GPL 代码与 MIT 代码混合使用，而不会违反任一许可证的条款。 Linux 人员一直使用内核 (GPL) 和链接设备驱动程序（GPL、MIT 等）来完成此操作。但是，如果您分发该应用程序，则必须分发整个派生作品的代码库，包括 GPL 许可软件和 MIT 许可软件，并且必须根据 GPL 将其许可给您的客户。
请查看我的页面 Squidoo 了解更多信息。
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.
我已经更新了所有 jQuery UI 源文件的版权以匹配 jQuery 核心的措辞。 http://github.com/jquery/jquery-ui/commit/536ae6189bf0f0de1113bf9ec7054da693544e1f
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明确禁止添加额外的限制，因此双重许可的唯一有效形式是允许用户根据GPL许可使用它或者根据MIT许可使用它（无论如何，这就是双重许可的含义）。
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).
jQuery 不再是双重许可的。 jQuery 项目现在仅在 MIT 许可证下分发，该许可证与 GPL 兼容。由于所有团队成员都签署了版权转让协议，大部分版权现在由 jQuery 基金会持有。非团队成员现在需要签署贡献者许可协议，但他们仍然保留其作品的版权贡献，就像他们以前所做的那样。我们已更新所有项目，以包含列出所有贡献者的 AUTHORS.txt 文件。您可以在最近的一篇博客文章中了解更多相关信息。
jQuery is no longer dual licensed. jQuery projects are now only distributed under the MIT license, which is GPL compatible. The majority copyright is now held by jQuery Foundation as all team members have signed a Copyright Assignment Agreement. Non-team members are now required to sign a Contributor License Agreement, but they still retain copyright of their contributions, just as they did before. We have updated all projects to include an AUTHORS.txt file listing all contributors. You can read more about this in a recent blog post.
我也不是一个层，但我认为“与”/“或”仅取决于观点。该代码根据两个许可证 (AND) 获得许可，而您可以根据任一许可证 (OR) 的条款使用它。
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).
IANAL 和您不应该从网站获取法律建议。但在我看来，关心许可的可能原因只有两个：
您想要使用代码。您需要版权所有者的许可，因此您必须根据版权所有者授予您的任何许可使用它。在这种情况下，您可以选择，因为它是双重许可的。同时在两个许可证下同时许可软件是一个逻辑矛盾，因为 GPL 增加了 MIT 许可证没有的要求。因此，作为用户，您可以选择其中之一。注意：如果您要分发代码，如果您自己的项目相应地获得了双重许可，那么您大概也可以继承双重许可。但是，如果您只想根据一个许可证的条款进行操作，则可以。
您想为代码做出贡献。在这种情况下，您需要知道您的代码也将获得双重许可。例如，通常不可能向 Linux 内核贡献任何非 GPLv2 的代码。如果您只想贡献 GPL 代码（因为您是 Copyleft 的坚定信徒），那么您必须意识到 jQuery 是 GPL AND MIT，这意味着您的代码必须类似 GPL 和 MIT。< /p>
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:
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.
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.