Mike Wasylik of Perpetual Beta has an interesting argument in the legendary GPL debate surrounding premium WordPress themes and plugins. He thinks that themes and plugins shouldn’t be required to be licensed under the GPL for the simple reason that they’re not derivative. U.S. copyright law defines a derivative work as one that physically includes a portion of the copyrighted work, which plugins and themes do not.
…even a theme or plugin that entirely dependens on WordPress to run at all, or simply improves WordPress in some way, would not be a derivative work and the GPL would not apply. For the vast majority of themes I’ve seen, the GPL would not apply because the theme is not, in my opinion, a derivative work. (In fact, if any one thing “incorporates” another, it’s most likely WordPress incorporating the theme, by use of the PHP
include() call, rather than the other way around.)
According to the article, the copy of the GPL included in every download of WordPress even states that a derivative work is “a work containing the Program or a portion of it, either verbatim or with modifications.” I’ve been making a similar argument for awhile now. I have yet to see a theme or plugin that actually incorporates WordPress into the plugin code itself, rather than being included by WordPress. It sounds to me like WordPress, if anyone, is the one doing the deriving…
Most WordPress themes and plugins are unique code for the most part, with a few hooks or function calls. I must have missed the memo that utilizing a third-party API makes your application a subset of the other software. (That would mean any desktop application would be a derivative of the operating system.)
A follow-up article from the same author makes the additional case that, whether the GPL applies or not, the Fair Use Doctrine can protect developers from the licensing terms of the original creator. The same laws that ensure you can quote part of an article without having to pay whatever licensing fee the publisher can cook up apply to software. As little, if any, WordPress code is used in a theme, it would likely be considered fair use.
I like some of the ideology behind the GPL, and quite a few software packages licensed under it. However, it seems that in this case one party is misusing (or misinterpreting) it to prevent small developers from earning a living while further enriching the WordPress community. For what reason, good intentioned or no, I cannot guess.