I think it’s time that the Software Freedom Law Center update their opinion on themes as derivative works. Since 2009, when this post (http://wordpress.org/news/2009/07/themes-are-gpl-too/) was written, WordPress themes have come a long way. The SFLC based their opinion on the “classic” and “default” themes included with WordPress 2.8. These themes were little more than the standard “loop” pages (index.php, page.php, etc.) and some code in functions.php but today’s themes are much more complex than that, with options panels, page builders, etc. Today’s themes have massive library folders with code that could easily work without WordPress. This additional code is not necessarily derivative of WordPress code, and therefore not necessarily subject to GPL. I think it is time that the SFLC re-evaluate their opinion on all PHP in themes being derivative.