It's kind of a combination of these two positions: something being a derivative work means that it requires an excuse under copyright law, whether that be a lic

It's kind of a combination of these two positions: something being a derivative work means that it requires an excuse under copyright law, whether that be a license, or a fair use defense (which may be fact-specific), or some other justification. Without such a justification, the derivative work is treated as a copyright infringement. This is a result of 17 USC §106(2), which says that one of the things that "the owner of a copyright [...] has the exclusive rights to do and to authorize" is "to prepare derivative works based upon the copyrighted work", unless an exception (including fair use) applies. https://www.law.cornell.edu/uscode/text/17/106 https://www.law.cornell.edu/uscode/text/17/106