This is OK and fair use: Training LLMs on copyrighted work, since it's transformative.
This is not OK and not fair use: pirating data, or creating a big repository of pirated data that isn't necessarily for AI training.
Overall seems like a pretty reasonable ruling?
I tend to think copyright should be extremely limited compared to what it is now, but to me the logic of this ruling is illogical other than "it's ok for a corporation to use lots of works without permission but not for an individual to use a single work without permission." Maybe if they suddenly loosened copyright enforcement for everyone I might feel differently.
"Kill one man, and you are a murderer. Kill millions of men, and you are a conqueror." (An admittedly hyperbolic comparison, but similar idea.)
I think that's the conclusion of the judge. If Anthropic were to buy the books and train on them, without extra permission from the authors, it would be fair use, much like if you were to be inspired by it (though in that case, it may not even count as a derivative work at all, if the relationship is sufficiently loose). But that doesn't mean they are free to pirate it either, so they are likely to be liable for that (exactly how that interpretation works with copyright law I'm not entirely sure: I know in some places that downloading stuff is less of a problem than distributing it to others because the latter is the main thing that copyright is concerned with. And AFAIK most companies doing large model training are maintaining that fair use also extends to them gathering the data in the first place).
(Fair use isn't just for discussion. It covers a broad range of potential use cases, and they're not enumerated precisely in copyright law AFAIK, there's a complicated range of case law that forms the guidelines for it)
(that's all to say copyright is dated and needs an overhaul)
But that's taking a viewpoint of 'training a personal AI in your home', which isn't something that actually happens... The issue has never been the training data itself. Training an AI and 'looking at data and optimizing a (human understanding/AI understanding) function over it' are categorically the same, even if mechanically/biologically they are very different.