In reply to mark k..

@mark k,

It's a pity you cloudied the issue by mentioning the Google v Oracle case. As I explain below, you've got that decision completely wrong.

However, on the more general point you make here, you are right. Just because some people like to repeat the peculiar mantra that themes and plugins are derivatives of WordPress does not make it true.

Whether a particular theme or plugin is or is not derivative will be strongly fact-dependent. For example, a plugin that just exposes functions within core will clearly be derivative. But a fully-fledged e-commerce or membership plugin is certainly not derivative.

That leaves a large gray area in between, where the answer would become clear only after protracted litigation. Unfortunately, some people behave as if scaring developers is an acceptable alternative.