The GNU General Public License (GNU GPL) is a legal document that governs the distribution of software. It is one of the most widely used free software licenses and is designed to guarantee the user’s freedoms to use, share, and modify software. Under the terms of the GPL, anyone can access and use the source code of software covered by the license. This means that they can also modify and distribute the software as they see fit, provided they give credit to the original authors and license their modified versions under the same terms. This allows for collaboration and innovation in the development of software, and helps to ensure that the knowledge and tools needed to use and create software are widely available to all. The GPL is a powerful tool for ensuring that software remains free and open source, and continues to be a vital part of the free software movement.
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.
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)
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)
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)