Ireneo Funes, after a riding accident, can forget nothing. He perceives every detail of every moment, remembers every leaf on every tree, and finds abstraction impossible because he sees only particulars. Borges's short story is a thought experiment about memory and its costs, about the forgetting that makes thought possible. Funes cannot generalize, cannot sleep, cannot live. He dies young of pulmonary congestion. The story is brief, lucid, and terrifying in its implications. Borges suggests that perfect memory would be perfect imprisonment. We are saved by what we lose.