If there’s anything in your code that relies on WordPress’s code (template tags, functions etc.), your work automatically becomes GPL by law (derivative code), whether you state it or not. There are exceptions in both themes and plugins, however. If a few elements do not depend on the WordPress at all, they may be licensed differently – such as css files and images.

And that is the main point, taken from “WordPress Licensing Guide for Theme and Plugin Developers” — and clearly defined what are really WordPress is licensed under GPL means, at least for me.

WordPress and GPL has become a big issue these days. Couple of days ago, there was a serious debate between Matt Mullenweg, co-founder of WordPress and Chris Pearson, developer of Thesis premium theme, over Twitter which then extended to Mixergy.

In short, Mullenweg disagrees with Pearson’s use of a license other than GPL for his Thesis theme. WordPress is built on the license of a GPL that has enabled hundreds of thousands of people to build amazing businesses off it. All it really says is that you can do whatever you like but anything built on top of the GPL must be GPL itself.

If you missed the Matt Mullenweg vs. Chris Pearson debate live debate yesterday at Mixergy, find the video at WordPress.TV

So, after reading that post; listen to the debate; with fully understands Drew Blas’ code of analysis, I just want to say, I’m fully agree with Matt. Just one thing, GPL says all thing running on WordPress should be GPL. Period.