The Silicon Dales Guide to Open Source Licencing

For some of our corporate clients used to paying for licences, Open Source can present the legal department with some challenges. This guide explains some of the terminology, the real-world application for the Open Source approach and where this has been tested in court. This guide will be of interest to legal departments and web services buyers, especially when replatforming from closed-source software.

An Introduction to Open Source

Open-source software (OSS) has a source code released under a license where the copyright holder grants users the rights to study, change, and distribute the software to anyone and for any purpose. Open-source software is also often developed in a collaborative public manner.


The GNU General Public License (GNU GPL or GPL) is a widely used free software license, which guarantees end users the freedom to run, study, share and modify the software. The license was originally written by Richard Stallman of the Free Software Foundation (FSF) for the GNU Project, and grants the recipients of a computer program the rights of the Free Software Definition.

The GPL is a copyleft license, which means that derivative work can only be distributed under the same license terms. This is in distinction to permissive free software licenses, of which the BSD licenses and the MIT License are widely used examples. GPL was the first copyleft license for general use.

Prominent free software programs licensed under the GPL include the Linux kernel.


The MIT License is a permissive free software license created at the Massachusetts Institute of Technology (MIT). As a permissive license, it puts  limited restriction on reuse, which results in wider license compatibility.

The MIT license permits reuse within proprietary software provided that all copies of the licensed software include a copy of the MIT License terms and the copyright notice. The MIT license is also compatible with many copyleft licenses, such as the GNU General Public License (GPL); MIT licensed software can be integrated into GPL software, but not the other way around.

As of 2015, it was the most popular software license on GitHub, ahead of any GPL variant and other free and open-source software (FOSS) licenses.

Notable projects that use one of the versions of the MIT License include Ruby on Rails, Node.js, jQuery, and the X Window System.


The terminology used for Open Source licencing can cause confusion when contrasted with the definitions used in closed-source licencing.

WordPress “Licences”

A purchased “licence” for a WordPress theme or plugin, is not a true licence. The “licence” is a token for download, support from the author and automatic updates. The true underlying licence is the GPLv2 (see below).


There is a catch – naming authors and giving credit. The key to the freedom associated with Open Source software is retaining attribution.

Forking versus Customisation

Essentially an issue of scale, anyone (usually a developer) can customise Open Source software, but if enough people (usually developers) decide to continue developing a distinct and separate version of a given software, it becomes a fork.

Open Source Licencing in Practice

The Licence

Check the licence here:

The license under which the WordPress software is released is the GPLv2 (or later) from the Free Software Foundation. A copy of the license is included with every copy of WordPress, but you can also read the text of the license here.

The latest version of the GPL is version 3, WordPress is released under GPLv2.

Test Cases

A number of potential test cases have been settled out of court, but a number have made it to the courtroom. Here are some notable precendents:

See Open Source in Practice

So you’re sold on the concept, now you want to know how it works and look at some examples.

Big Companies using Open Source

Nearly every big company uses Open Source software somewhere along the line, though some organisations have made large public commitments to Open Source as a movement and a business imperative:

Major Open Source Events

Get Open Source for your Business

Your organisation probably already uses Open Source. However, to fully leverage the benefits of Open Source, get in touch with Silicon Dales.