GPL and open source are important factors behind WordPress Sucess still some users don’t really understand what exactly GPL licence is and how GPL licence for WordPress works.
The GPL is an open-source software licence that is designed to protect four fundamental freedoms that are considered to underpin “free software”, namely, the freedom to:
- Run the software for any purpose;
- study how the software works through access to source code and to freely adopt it;
- redistribute copies of the software to anyone; and
- improve the software, and redistribute those improvements to anyone.
GPL Versions
First written by Richard Stallman and the Free Sofware Foundation (FSF) in 1989, the GPL has continued to evolve through successive versions.
Version 2 was released in 1991 and version 3 was released in 2007. Version 3 is the latest version.
Whilst WordPress is released under version 2 of the GPL, the introductory section in the licence now states that “you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Sofware Foundation; either version 2 of the License, or (at your option) any later version”.
Clauses or paragraphs in the GPL are called “sections”.
Understanding the GPL
From the perspective of opening up software for use by others, the GPL was and remains a well-crafted open source licence.
At the same time, it uses legally-oriented language with which many WordPress users may be unfamiliar.
In addition, and unlike the Creative Commons licences for other forms of copyright works, the GPL doesn’t have a simplified “human-readable deed” (as Creative Commons calls the summary of its licences).
For these reasons, the true meaning and impact of the GPL might not be immediately apparent to some WordPress developers, designers and users.
To boil things down, the following table summarises key aspects of version 2 of the GPL.
It doesn’t summarise all clauses. Rather, it summarises those that are most relevant to WordPress users on a day-to-day basis.
1 Copying and distribution
You may copy and distribute the program as long as you comply with some copyright notice and disclaimer requirements.
Those requirements are that you publish on each copy an appropriate copyright notice and disclaimer of warranty, keep intact all notices that refer to the GPL and the absence of any warranty, and give recipients a copy of the GPL along with the program. (Section 1)
2 Fees
You may, if you wish, charge a fee for transferring a copy of the Program and/or for warranty protection. (Section 1 as well)
3 Modifications / derivative works
You may modify the Program or any part of it and distribute the modifications or new work as long as modified files contain notices regarding the existence and date of changes and any work that you distribute or publish that contains or is derived from the Program or any part of it is licensed as a whole at no charge to all third parties under the GPL. (Section 2)
4 Distributing non-source forms
You may copy and distribute the Program or a work based on it in object code or executable form, on the terms of sections 1 and 2, as long as you accompany it with either:
- the complete corresponding machine-readable source code; or
- a written offer (valid for at least 3 years) to give any third party the source code, for a charge that is no more than the cost of distribution; or
- information you received as to such offer (this option is allowed only for noncommercial distribution and if you received the non-source form(s) with such an offer. (Section 3)
5 Termination
If you copy, modify, sublicense or distribute the Program other than as permitted, your rights under the GPL will terminate automatically. (Section 4)
6 Downstream licensing
Downstream recipients of the Program or any work based on it automatically receive a licence from the original licensor to copy, distribute and modify the Program on the terms of the GPL.
As a distributing licensee, you are not allowed to impose any further restrictions on the recipients’ exercise of the rights under the GPL. (Section 6)
The GPL in a small nutshell
A super-condensed summary would be along these lines: you can copy and distribute the program, you can charge a fee for transferring the program or providing warranty protection, and you can modify the program and distribute your resulting derivative work.
But, if you distribute your derivative work, you need to license it under the GPL, otherwise, your licence to use the program will terminate (and you’ll be infringing copyright in the program).
Commonly asked questions regarding GPL Licence in WordPress Community
If I modify the core WordPress software or a GPL’d theme or plugin, must I release the source code of the modified versions(s) to the public?
If you are using the modified version privately without distribution, then you do not have to release the source code of the modified version to the public. However, as the Free Sofware Foundation puts it, “if you release the modified version to the public in some way, the GPL requires you to make the modified source code available to the program’s users, under the GPL.”
If I know that someone has developed a WordPress theme or plugin for private use, can I require that person to give me a copy of the theme or plugin?
No, the GPL does not require this.
I take a GPL’d theme or plugin from the WordPress theme or plugin repository, or I purchase a GPL’d theme or plugin from a commercial provider, and then I modify the theme or plugin for my own purposes. Am I obliged to release my modified version to others?
No, you are not obliged to release your modified version to others.
Can I sell the core WordPress software for a fee if I want to?
Yes. Doing so is consistent with the freedoms in the GPL. However, trying to do so would be pointless and unlikely to earn you any money, as everyone knows or could easily find out that WordPress is freely available at wordpress.org.
I’m a theme/plugin developer. I’ve put huge effort into writing my theme/plugin and I’m going to release it under the GPL but I want to make sure that everyone who receives my theme or plugin, even if from someone else, is obliged to pay me a licensing fee or notify me that they have it. Can I do that?
No. As the Free Sofware Foundation puts it, the “GPL is a free software license, and therefore it permits people to use and even redistribute the software without being required to pay anyone a fee for doing so.”
Similarly, if someone receives a copy of GPL’d software, that person does not have to inform the developer that s/he has it. You are entitled to charge a fee for access to support and later versions, but this is quite different from requiring recipients to pay a licensing fee for merely using the software.
I’m a commercial theme or plugin developer. I sell my GPL’d theme or plugin online, behind a paywall. People can only access the theme or plugin files after paying my prescribed fee. Does the GPL allow me to do this?
Yes. You are entitled to charge a fee for distributing copies of GPL’d software. Note, however, that anyone who obtains a copy is entitled to release it to anyone else, with or without charge; the GPL allows this to occur.
I’m the same commercial theme or plugin developer mentioned above, selling my GPL WordPress plugins or themes online behind a paywall. As a commercial operator distributing a GPL’d program, am I obliged (e.g., if someone asks) to make my theme or plugin available to a member of the public for free?
No. However, as noted above, anyone who obtains a copy is entitled to release it to anyone else, with or without charge.
I’ve purchased some fully GPL’d themes or plugins from a commercial theme or plugin provider. May I sell those themes or plugins from my own website for my own benefit or publish those themes or plugins on my own website and give them away for free?
Yes, under the GPL, you may do either of these things (or both on separate sites if you were so inclined).
You’d also need to be careful not to infringe others rights that the commercial theme or plugin provider may have.
I’m happy for other people to use my themes and plugins for free. Indeed, that’s why I released them under the GPL and put them in the WordPress theme or plugin repository. I would, however, like to be acknowledged as the author of the theme or plugin in cases where users share the theme or plugin with others or modify the theme or plugin. Can I require that?
Yes. As the Free Sofware Foundation puts it, you “can certainly get credit for the work. Part of releasing a program under the GPL is writing a copyright notice in your own name (assuming you are the copyright holder). The GPL requires all copies to carry an appropriate copyright notice.”