Lorraine Boissoneault in Smithsonian:
Rene Descartes, a 17th-century French philosopher who traveled widely across Europe, deeply considered the question of what made us human. It’s no coincidence that his most famous quote is repeated by one of the replicants in Blade Runner: “I think, therefore I am.” And if all that isn’t enough proof of his connection to the film, consider the names: Descartes and Deckard. As philosopher Andrew Norris points out, Descartes suspected there might someday be a need for a test of whether something was human or machine. “If there were machines bearing images of our bodies, and capable of imitating our actions as far as it is morally possible, there would still remain two most certain tests whereby to know that they were not therefore really men,” Descartes wrote. So he created his own tests, which relied on linguistic ability and flexibility of behavior. Replicants speak and behave just as humans do, meaning they would pass Descartes’ tests. But there’s another reason Deckard struggles to disprove their humanity: Replicants also have implanted memories. For English philosopher John Locke, what gives a person a sense of self is the continuity of their memories. The human body changes with time, but memories remain, offering a foundation for a stable identity. “As far as this consciousness can be extended backwards to any past Action or Thought, so far reaches the Identity of that Person,” Locke wrote.
So for Blade Runner’s Rachael, the most advanced replicant yet developed, it doesn’t matter that she might only be a few years old; her memories stretch back much further, giving her the impression of having lived much longer. That’s what makes Rachael such a tragic figure—”her” memories don’t belong to her. They come from her inventor’s niece.