Oracle, owner of Java, is suing Google over the programming language they use in Android phones. Its a near clone of Java*. Specifically, Oracle is alleging that Copyright prevents Google from using the Java API.
Oracle isn't suing Google for having copied their source, binaries or documentation**, but the API itself (package ... provides class ... with methods ... with signatures ...). Their argument could be summarised as follows: Creating the API involved a lot of hard creative work, so it aught to be covered by Copyright.
An argument Google is making is that a language is useless without APIs, so the APIs are part of the language. Since languages aren't covered by Copyrighted, neither are APIs. The judge brought up***:
No decision on point that says that computer languages have not been copyrightable.
I believe there's no past decision on this because everyone in the industry operates with the understanding that computer languages (e.g. Perl, not perl) aren't Copyrightable.
While I recognise that creating a good API is indeed a difficult task, I don't see how that makes them Copyrightable. APIs are intangible information, while Copyright only applies to work that have been fixed to a medium. In other words, Copyright covers expression (e.g. documentation), not ideas or facts (e.g. APIs, languages).
Is that how you see it?
PS — Groklaw has excellent detailed coverage of the case.
* — I don't know what Google calls it, but it probably not Java because Google doesn't have the rights to that trademark, and there's no allegations of trademark infringement. Google would have to pass a certification progress ("TCK") to get a license to use the name Java.
** — Well, there are 9 lines of code in contention (among hundreds of thousands), but that a very minor aspect of this case. Google uses a combination of GPLed Java sources and a clean-room implementation of others.
*** — These may not be his exact words. They come from a citizen reporting in court for web site Groklaw.