Function calls aren’t governed under GPL rules, else ALL computer software would run into the statement you made there. All software makes function calls to the software below it, making it dependent on the code, but NOT derivative.

In the Galoob vs. Nintendo court case, the courts made that point very explicitly clear:

Some time ago, for example, computer companies began marketing spell-checkers that operate within existing word processors by signalling the writer when a word is misspelled. These applications, as well as countless others, could not be produced and marketed if courts were to conclude that the word processor and spell-checker combination is a derivative work based on the word processor alone.

products dependent on the software must also be GPL

GPL covers “derived from” NOT “dependent upon”, which is where this entire mess starts.

@Chip Bennet -

The Linux-Firefox analogy is completely non sequitur, and in no way applies to WordPress and WordPress themes.

A better example would be Ubuntu and its various derivatives. A non-GPL package can run on either distro, but because Ubuntu is GPLed, so too must any of its derivatives be GPLed.

Firefox isn’t an editorial revision of, annotation to, elaboration upon, or other modification of Linux. Firefox doesn’t depend upon Linux to exist or to run. It clearly isn’t a derivative work of Linux.

Ubuntu Netbook Remix, on the other hand, clearly is a derivative work of Ubuntu.

Your analogy here is worse than the Firefox/Linux analogy. Thesis isn’t WordPress re-wrapped and bundled as a separate application, as in the case of a Linux distribution derived from Ubuntu.

And if it’s GPL, then the GPL license is granted from the original (WordPress) and not from Thesis. Now, infringing on CSS, TM and/or images is different, but I don’t think Chris has a case for infringement on code, as the licensed code doesn’t originate with him.

But it looks like this is a case of style cloning, not code copying. In which case, Chris is a douche, but it has nothing to do with the GPL. Any theme explicitly attempting to copy the “look and feel” of popular news sites or of sites like facebook, twitter or is probably violating copyright if not TM.

[P.S. You can get protection (copyright, TM, etc.) on "look and feel". It's more established and understood in copyright law then anything related to css/html or code. I believe the measure is you can't make something look so like a competitor as to cause a potential misidentification. Something so generic as a framework though shouldn't fall under this.]

I find myself agreeing almost entirely with Chip for a change :), but if the output matches exactly, and the code different, see “look n feel” infringement above.)