Does WordPress being under GPL actually necessitate that the tools created for it (plugins, themes) must also be under GPL? Is so, then why?

I'm confused about this idea that because WordPress is under GPL, the plugins and themes all have to be under GPL as well. My understanding of GPL includes that you can't distribute something that is partially GPL and partially proprietary; but if you distribute a proprietary plugin, shouldn't it be fine for a user to use that plugin within their GPL copy of WordPress? The problem should only arise if the user tries to distribute their WordPress installation along with the proprietary plugin, because now they are distributing something that violates GPL. Hosting a website that uses both GPL and proprietary content does not violate the GPL license as hosting a site is not usually interpreted as distribution of its content (clearly, copyrights still apply).

If WordPress won't allow you to add a plugin to https://wordpress.org/plugins/ that isn't GPL, that's fine. But there isn't anything wrong with sharing a proprietary plugin elsewhere, right?

Maybe if your proprietary plugin calls a WordPress function, say, wp_get_current_user(), then someone could claim that your plugin violates GPL because it references something from GPL while being itself proprietary? I'm not sure of this, but it's the best explanation I've thought of.

In refutation to the suggestion in my last paragraph, here is an analogous situation: https://askubuntu.com/questions/346514/is-steam-for-linux-an-open-source-application-does-it-deserve-to-be-on-linux. Linux is under GPL; Steam for Linux is not. Like what I had been suggesting in the case of WordPress plugins, it's up to the user whether they will use it.

Topic licensing Wordpress

Category Web

1
answered at

The official WP line is that if you want to share sell or distribute your plugin/theme, then the PHP code must be GPL compatible. This is because GPL is a copyleft licence. The WP project, maintainers, and governance follow the same interpretation of this that the FSF and others do, the same interpretation being used to sue the TV maker Vizio in court for not distributing source despite using opensource libraries.

Some people may disagree with this interpretation, but that is a legal subject and beyond the scope of this site. I am not a lawyer and it is for the judge in that case to set the precedent.

Your other points though, are covered by the FAQ on the GNU website:

https://www.gnu.org/licenses/gpl-faq.html

The GPL does not prevent you from selling themes and plugins, and going non-GPL does not prevent piracy or provide other protections ( and it's questionable that a "proprietary" licence would even be valid or enforceable ). The biggest businesses in the WP ecosystem still make plenty of money with GPL source code.

What I can say is that:

  • Your plugin will never be allowed on wordpress.org
  • Other marketplaces will probably not host you
  • Other plugin businesses in the WP ecosystem will not want to do business with you, limiting your ability to promote and cross-sell
  • Applications to speak or volunteer at official WordPress conferences will be blocked
  • Sponsoring official WordPress events will be impossible
  • Many prominent community members will see it as a hostile and unnecessary step
  • Many large agencies will avoid your product
  • Larger enterprise businesses will have compliance issues around this
  • Some hosts may refuse to allow your code
  • Many will consider it a sign of shady practices
  • Some businesses that have made a point of not using GPL compatible licenses have had... not so pleasant interactions with the BDFL

If despite this, you still wish to pursue a proprietary licence that is not compatible with the GPL, and distribute this, you should seek legal advice from a lawyer specialising in these matters. You shouldn't be asking for legal advice online.

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