"Notably, Judge Bibas ruled in Thomson Reuters’ favor on the question of fair use. The fair use doctrine is a key component of how AI companies are seeking to defend themselves against claims that they used copyrighted materials illegally. The idea underpinning fair use is that sometimes it’s legally permissible to use copyrighted works without permission—for example, to create parody works, or in noncommercial research or news production. When determining whether fair use applies, courts use a four-factor test, looking at the reason behind the work, the nature of the work (whether it’s poetry, nonfiction, private letters, et cetera), the amount of copyrighted work used, and how the use impacts the market value of the original. Thomson Reuters prevailed on two of the four factors, but Bibas described the fourth as the most important, and ruled that Ross “meant to compete with Westlaw by developing a market substitute.”"