There’s a term that pops in the WordPress community, “split license”, that we should put to rest. It’s sloppy at best, misleading at worst.

First, some background. WordPress is under a license called the GPL, which basically says you can do whatever you like with the software, but if you distribute changes or create derivative works they also need to be under the GPL. Think of it like a Creative Commons Sharealike license.

In the past people weren’t sure if themes for WordPress were derivative works and needed to be GPL. In 2009 we got an outside legal opinion that cleared up the matter saying that the PHP in themes definitely had to be GPL, and for CSS and images it was optional. Basically everyone in the WP community went fully GPL, sometimes called 100% GPL, for all the files required to run their theme (PHP, JS, CSS, artwork). The predicted theme apocalypse and death of WordPress didn’t happen and in fact both theme shops and WordPress flourished, and best of all users had all the same freedoms from their themes as they got from WordPress. It was controversial at the time, but I think history has reflected well on the approach the WP community took.

As I said the PHP has to be GPL, the other stuff can be something else — many people started to use the term “split license” or “split GPL” to describe this. The problem, especially with the latter, is it leaves out the most important information. “Split GPL” doesn’t say whether the theme is violating WordPress’ license or not (maybe it’s proprietary PHP and GPL CSS), and more importantly doesn’t say what the non-GPL stuff is, which is the part you need to worry about! It also makes it sound like a split license is a thing, when all it really means is there are different licenses for different parts of the work. If something has a “split license” you have no idea what restrictions or freedoms it provides.

If someone decides to have different licenses for different parts of a theme they ship in one package, it’s probably worth taking a few extra words to spell out what the rights and restrictions are, like “GPL PHP, and a restrictive proprietary license for all other elements included with the theme.” This is really important because if you’re a smart WordPress consumer you should avoid proprietary software, there is always a GPL alternative that gives you the rights and freedoms you deserve, and probably is from a nicer person who is more in line with the philosophy of the rest of WordPress. Vote with your pocketbook, buy GPL software!