Thesis and the GPL

If the answer is yes, then blob of code X is not a derivative work of blob of code Y. You can distribute X without any liability for direct copyright infringement of Y's copyrights.

Third party U might combine X and Y in memory, forming a derivative work of both X and Y. If the license of Y does not allow this, then U would be guilty of copyright infringement of Y.

It is possible that the developer of X could also be liable for U's infringement, if X essentially is only useful in cases where someone (like U) is using X to infringe Y. This is called contributory infringement.

In the case where the license of Y is GPL (or pretty much any other free software or open source license...), U's actions are not an infringement. If U's action are not an infringement, then X cannot be liable for contributory infringement.

I've not written any Wordpress themes, so don't know what you need to actually write one. Do you need to actually have the Wordpress source code in order to write a theme? Or do you only need a list of functions available in that code and their interfaces and a description of what they do? If the latter, then a theme would NOT automatically be a derivative work, and hence would not automatically need to be under GPL.

Much of this has already been litigated, going way back to the early video game systems, when third party game companies started releasing unauthorized game cartridges. When the user inserts a game cartridge, a single work is formed in the console comprising the system software and the game software. The game software makes calls to functions in the console. The console makers tried almost the same argument the SFLC makes in their analysis that someone else posted here. The console makers lost. This is one of the main reasons that consoles nowadays rely on technology (such as loaders that only load code signed by the console maker), not law, to keep out unauthorized third party games.

EDIT: I'm with spacemonkey (referring to how joomla manages it): http://apeatling.wordpress.com/2010/07/14/thesis-and-the-gpl...

You can look at technicalities, like how wordpress designs its API, but those are not faults of the themes.

What is a theme actually? It's a look and feel, and this look and feel is not dependent on wordpress. A theme could exist across many different blogging platforms. Each platform will provide a different API for the theme to interact with it, but the look and feel of the theme has nothing to do with this interface. The theme is a conceptual abstraction that is in no way dependent on the existence of wordpress as another conceptual abstraction.

As such, I believe that the thesis theme should not be GPLed.

Are people really this desperate to force their license of choice on others? No harm is being done to Wordpress by this, and if they really care, they can switch to a license that explicitly states how they wish their product to be used.