WordPress, Themes and the GPLv2

by Rob Hassett and Mike Schinkel


There has been a long brewing debate in the software world regarding whether commercial developers who write and distribute their own separate code to work with software licensed using version 2 of the GNU General Public License must license their software under that version of the GPL.

In the summer of 2010 a debate emerged on blog posts and via Twitter regarding this issue between Matt Mullenweg, founder of WordPress, Automattic and the WordPress Foundation, and Chris Pearson founder and CEO of DIYThemes. Mr. Mullenweg and Mr. Pearson resolved their differences. However the question they addressed remains unanswered.

We read many of the postings on this topic, most of which were very informative and for which we are grateful. Our goal is to provide an objective and dispassionate view of the relevant license in hopes to establish some clarity regarding the issue.

This article does not constitute legal advice and is general information only.


WordPress is software that is used to create blogs and websites, including the website on which this article is posted: www.internetlegals.com. It is open source and is licensed to others under Version 2 of the General Public License, administered by the Free Software Foundation (the “GPLv2“). To operate WordPress must have what is referred to as a “Theme” which is a collection of scripts, images, and other files that collectively establish the look and some of the functionality for a website based on WordPress and WordPress itself currently includes one default Theme. Many developers, including commercial developers, offer other Themes, Plugins and other software and services for use with WordPress.

A user may separately download and install WordPress and a Theme. The user then separately opens the programs and activates the Theme, which interacts with WordPress to create websites and/or blogs.

Chris Pearson created a Theme named “Thesis “which became a popular Theme for use with WordPress. Matt Mullenweg contended that Thesis was a “work based on WordPress,” under the GPLv2, which, if true, would have serious legal consequences discussed below. Chris Pearson said it was not.

There is some indication that at some point in the past and maybe currently some of the Thesis code was copied from WordPress code. If that was true at the time of the dispute, there is no question that Thesis was subject to the requirements of the GPLv2, but that possibility is not the subject of the debate. The debate, and the focus of our analysis, is over whether add-on software, such as Theme software, that does not incorporate any code from a prior “Program,” licensed under the GPLv2, may be subject to the requirements of the GPLv2. We are not aware of any court decision that has clearly answered this question.

Requirements of the GPLv2

A developer may choose whether or not to comply with the GPLv2 with respect to a particular Program. However, if the developer copies, prepares derivative works of or distributes that Program without complying with the terms of the GPLv2, the developer would be liable for copyright infringement. If all the developer does is copy, use, study and modify the Program, without distributing it, the GPLv2 license does not require the developer to do anything.

However, if the developer distributes either the Program or a “work based on the Program,” the developer is required to meet certain requirements including, but not limited to, licensing the Program, and any “work based on the Program,” under the GPLv2 and making the source code available. So if a developer creates a “work based on the Program”, that developer may sell copies of it, but is required to provide the source code, if asked, and the purchaser is entitled to make and distribute copies of such new work in competition with the developer. It is the authors’ understanding, based on hearing Mr. Pearson’s comments on the audio interview where he discusses this issue with Mr. Mullenweg, that Mr. Pearson did not want to enable his customers to sell copies of Thesis in competition with him.

The relevant legal question then is whether a Theme that does not include code from WordPress, but works together with WordPress, will constitute a “work based on the Program” under GPLv2. If so, its distribution without compliance with the GPLv2 constitutes copyright infringement. If it is not, its distribution without compliance is permitted.

GNU and WordPress Views

Attorneys who are associated with the open source movement say that a portion of most Themes constitute “works based on WordPress.”

The following is posted on the GNU website under “Frequently Asked Questions” relating to GPLv2:

If a program released under the GPL uses plug-ins, what are the requirements for the licenses of a plug-in?

It depends on how the program invokes its plug-ins. If the program uses fork and exec to invoke plug-ins, then the plug-ins are separate programs, so the license for the main program makes no requirements for them.

If the program dynamically links plug-ins, and they make function calls to each other and share data structures, we believe they form a single program, which must be treated as an extension of both the main program and the plug-ins. This means the plug-ins must be released under the GPL or a GPL-compatible free software license, and that the terms of the GPL must be followed when those plug-ins are distributed.

If the program dynamically links plug-ins, but the communication between them is limited to invoking the ‘main’ function of the plug-in with some options and waiting for it to return, that is a borderline case.

The following are portions of an opinion of James Vasile of the Software Freedom Law Center, which was posted by Matt Mullenweg on the WordPress website:

You asked the Software Freedom Law Center to clarify the status of themes as derivative works of WordPress, a content management software package written in PHP and licensed under version 2 of the GNU General Public License.

On the basis of that version of WordPress, and considering those themes as if they had been added to WordPress by a third party, it is our opinion that the themes presented, and any that are substantially similar, contain elements that are derivative works of the WordPress software as well as elements that are potentially separate works. Specifically, the CSS files and material contained in the images directory of the “default” theme are works separate from the WordPress code. On the other hand, the PHP and HTML code that is intermingled with and operated on by PHP code derives from the WordPress code.

The PHP elements, taken together, are clearly derivative of WordPress code. The template is loaded via the include() function. Its contents are combined with the WordPress code in memory to be processed by PHP along with (and completely indistinguishable from) the rest of WordPress. The PHP code consists largely of calls to WordPress functions and sparse, minimal logic to control which WordPress functions are accessed and how many times they will be called. They are derivative of WordPress because every part of them is determined by the content of the WordPress functions they call. As works of authorship, they are designed only to be combined with WordPress into a larger work.

HTML elements are intermingled with PHP in the two themes presented. These snippets of HTML interspersed with PHP throughout the theme PHP files together form a work whose form is highly dependent on the PHP and thus derivative of it.

These writers focus on one or both of the following:

(1) the fact that the PHP that is incorporated into the Theme has to correspond with the PHP in WordPress, and

(2) the fact that there is heavy and extensive interaction between the Word Press and the Theme software.


“A work based on the Program” is defined in the GPLv2 as follows:

 A “work based on the Program” means either the Program or any derivative work under copyright law: that is to say, a work containing the Program or a portion of it, either verbatim or with modifications and/or translated into another language.

If this definition had ended with “any derivative work under copyright law,” it would be necessary to determine the meaning of the term “derivative work” under the Copyright Act. Instead the GPLv2 defines the term for us. To the extent important here the phrase is defined as:

a work containing the Program or a portion of it, either verbatim or with modifications

Any developer creating Themes for WordPress would generally need to either examine the WordPress software, or material about that software, to be able to understand how to create the Theme. The Theme would need to be able to communicate with, provide instructions to and receive instructions from the WordPress software. However the Theme would not need to contain any part of the WordPress software or a portion of it, either verbatim or with modifications. Therefore what is distributed would not need to be the “WordPress software or any work based on the WordPress software.”

The fact that PHP in the Theme software has to correspond with the PHP in the WordPress software is not legally relevant to whether the Theme software that is distributed contains all or portions of the WordPress software. Likewise, the fact that a lot of interaction happens between WordPress and the current active Theme after that Theme is distributed to an end user is also legally irrelevant to whether the Theme itself contains all or any part of the WordPress software.

Therefore, inasmuch as the commercial vendors of Themes, including Thesis, are able to avoid including any of the WordPress source code in those Themes, such vendors should be able to avoid being required to take any action to be in compliance with the GPLv2 .


Under the totally different language of the GPLv3, which was first made available for use in 2007, a provider of software, such as WordPress, would have a much stronger claim that distributing Themes without making the source code available to potential competitors was an infringement.

The revisions in the GPLv3 will not help WordPress require Themes to be licensed via GPL. WordPress, and its revisions, were licensed under the GPLv2, without any language permitting licensees to use a later version, and as such there is no actions its controllers could take that would cause future versions of WordPress to be subject to the GPLv3.

Advocacy of GPL-licensing of Themes

Even though our analysis tells us there is no legal requirement for commercial Theme vendors to license Themes for WordPress using GPLv2 we expect there will still be a strong interest on the part of “the WordPress community” to see that most if not all Themes are and/or continue to be licensed via GPLv2. One of the authors, the one who is a participant in the WordPress community, actively supports this ideal.

As such we suggest to Automattic, to WordPress and its foundation, and to the WordPress community at large that they collectively work to continue to encourage Theme vendors to license their offerings via GPL, and that they proactive look for ways to help ensure those who would otherwise choose not to license via GPL are enticed to do so because of the collective benefits they gain from the supportive community.

Or said more simply, without the GPLv2 to require Themes to be licensed via GPL it becomes an “unregulated market” and the WordPress community should employ classic market incentives to encourage adoption of the GPL.

Advisability of Settling Dispute

As far as whether Mr. Pearson’s settling was a smart move, it very likely was. First, if any of the WordPress code was copied into Thesis, his application was governed by the GPLv2 regardless of whether a court agreed with our analysis. Second, litigation is very exhausting and expensive and regardless how sure anyone is about what is the correct answer to a legal question, it is not possible to know how a court will rule. All that a lawyer can provide is an opinion. Third, he was having to deal with marketing and public relations pressure from the WordPress community that likely outweighed the value of not complying.

Rob Hassett is an attorney in technology, entertainment and corporate law with Casey Gilson P.C. in Atlanta, Georgia. He also is a co-author of volume 5, on Internet and Interactive Media law, of the ten volume publication entitled “Entertainment Industry Contracts,” published by Lexis/Nexis and has, on many occasions, taught in the Professional Education Program at Georgia Tech. Mr. Hassett is the founder, editor and publisher of this website: TellMeSomethingIDontAlreadyKnow.com

Mike Schinkel is an entrepreneur in Atlanta, Ga. He was founder and CEO of catalog mail order retailer Xtras, Inc that was recognized in 1999 by the Inc 500 as #123 fastest growing private company in the USA. Today Mike is an active participant in the WordPress developer community, a consultant advising companies on their WordPress Business Strategies, a software developer building WordPress plugins for those companies, and a co-founder of and partner in The Business Of WordPress Conference.

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