Is it legally and/or ethically okay, to build a business based on a GPL licensed software? To those of you unfamiliar with the not-so-uncomplicated details of open and commercial licensing, this question may sound like a question you’d ask a student of media law. But theory turns into virtual reality when we take a closer look a Thesis, a very popular WordPress theme.

Unlike most themes, Thesis isn’t available for free. Christ Pearson is selling his template for $87 per personal site, and so he’s been racking up sales. Why do people pay for Thesis when there are so many free themes available? This question is a lot easier to answer: Chris thought about what pro customers want and started to offer a flexible, highly configurable theme which caters almost every need of professional publishers and pro-bloggers. But even though his sales figures are skyrocketing, Matt Mullenweg, founder and head of argues that Thesis violates the GPL license – because GPL-software not only is freely available (in source code), but the GPL (Gnu Public Licenses) also states that all products built upon GPL software must also use the same license. In other words: It’s illegal to make money on the hard (and free) work of others.

Today invited Chris and Matt for a Skype discussion which covers some very important aspects of software licensing:

In my opinion, Matt is right but Chris is not the bad guy here. I definitely think that programmers should be compensated for their work – after all, if Chris hadn’t sold Thesis but given it away freely, he probably couldn’t put so many development resources into his flagship product.

The same problem actually applies to many popular plugins I use on this blog: Ajax Edit Comments and PrettyLink are both available as pro version. I happily spend a couple of dollars on plugins that offer great value. (When it comes to software, “great value” in most cases means that it’ll help you to save time and work, or in this case blog, more efficiently.) Yet still, the GPL license must not be violated. After all, we all profit enormously from freely available software. And even though I understand Chris’ position, he tends to exaggerate: Thesis is a nice theme, but stating that it was the one crucial factor which made commercial webmasters chose WP is just ridiculous: here in Europe, many companies use WordPress, but Thesis is widely unknown.

So how can we solve this conflict? Can vendors of pro plugins / themes change their business model to offering the software for free but offer paid support? The programmers of PrettyLink and Ajax Edit Comments chose a different approach. In both cases, there’s free version (available in the WP repository) and a pro-version available on the author’s website after payment. Legally, this doesn’t count though: no plugin or theme is a stand-alone software: without mothership WordPress, the code is useless – that’s what “builds on GPL software” means. Seems like this discussion will keep going on for a while. What’s your opinion on paid WordPress themes and plugins?