>Do you oppose copyright on all software, i. e. source code, as well?
That has nothing to do with anything. Copyright is a human construct. Somethings are decided to be copyrightable and somethings are not. Not every creative endeavor should be copyrighted, other should, and other should with major limitations. APIs were never copyrightable. Ever. The computing and programming industry developed with this assumption - in fact, it may not have ever developed if that wasn't the case. Why does this need to change now? And not even through a new law but rather court re-interpretation.
My point is that there should be some criteria that determine if something should fall under copyright. And I'm having a hard time finding such a set that contains source code but does not include a (sufficiently extensive) API.
You're just asserting tradition. Yet you are not addressing my examples that directly show precedent within the industry for recognising copyright for APIs.
As I undestand it, there is a principle that legal contracts themselves cannot be copyrighted, despite the fact that they might well be the result of a considerable amount of creative work. The underlying principle here is that the legal effect itself cannot be subject to exclusive ownership, and the only way to get the same legal effect is to have the same contract.
I believe APIs can be considered under an analogous principle - that is, the ability to interoperate with a set of existing code shouldn't be subject to exclusive ownership, and you can't interoperate with the same existing code without implementing the same API, so APIs should not be copyrightable. (This draws a distinction between the API itself and the underlying implementation of that API).
That has nothing to do with anything. Copyright is a human construct. Somethings are decided to be copyrightable and somethings are not. Not every creative endeavor should be copyrighted, other should, and other should with major limitations. APIs were never copyrightable. Ever. The computing and programming industry developed with this assumption - in fact, it may not have ever developed if that wasn't the case. Why does this need to change now? And not even through a new law but rather court re-interpretation.