This text is included in the license.txt file in the base of our plugin and represents the current license for Paid Memberships Pro:
Paid Memberships Pro Copyright (C) 2011-2018 Stranger Studios, LLC
Paid Memberships Pro uses the same software license as the current version of WordPress: GPLv2. You can get the text of that license in the license.txt file of your root WordPress directory or online at https://www.gnu.org/licenses/old-licenses/gpl-2.0.html.
Please read the GPLv2 for full details, but what this means in practice is that you may install this plugin on any site for personal or commercial use. You may redistribute this plugin any way you choose as long as you maintain the GPLv2 license. If you distribute an altered version of this code, we ask that you:
1. Give your software a name other than “Paid Memberships Pro” or “PMPro” to avoid confusion.
2. Disable the upgrade functionality (includes/upgradecheck.php) to avoid contamination of your distributed plugins or our upgrade services.
3. Notify us of your distributed version so we can potentially promote the distribution if it’s a good effort.
Why GPL?
- Paid Memberships Pro is a WordPress plugin.
- WordPress uses the GPL license.
- The folks at WordPress consider plugins and themes “derivative works”.
Therefore the GPL applies to all WordPress plugins, including Paid Memberships Pro. And so Paid Memberships Pro must use the GPL license.
Controversy
Some people may argue against #3 above, and say that not all plugins are derivative works. We disagree and further believe that even if you don’t believe that the GPL is legally applicable to your plugin, it makes business sense to be on the same side as the software you are building your business on.
Why No Split License?
A split license typically means offering your PHP and other executable code as GPL while using a more restrictive license for HTML, CSS, Javascript, and images. This is appealing because it allows one to legally abide by the GPL while adding restrictions that will make it harder for people to distribute your code without breaking the secondary license.
We considered using a split license, and I think it still makes sense for some themes and plugins. However, for Paid Memberships Pro, using a split license would be against the spirit of the GPL.
A split license is a “hack” to discourage people from redistributing a plugin. The real value of our plugin is not in the HTML, CSS, Javascript, or images… although they (or replacements) are necessary to get the plugin to work. The value is in the code itself and how it works together with WordPress. So we plan to charge for access to our plugin. But because it is GPL, we can’t restrict our customers’ use of the plugin.
What about the three “requests” in your license.txt?
From my understanding of the GPL, the 3 requests we ask of people distributing copies of Paid Memberships Pro are allowed and fairly standard. (Think of all the different “flavors” and names for Linux distributions.) We are not trying to keep people from distributing the code, but we are trying to avoid confusion (the version called “Paid Memberships Pro” is the one we maintain) and other badness (you obviously want to stop pinging our upgrade servers if you change your version of the code).
I always aim for straight forward language and requests in our legal documents. That’s what I’m doing here. If there is something wrong or unkosher about that text, I am open to revising it.