I ask students to bring their baby or early childhood pictures to class. After they try matching names with images of their classmates, I ask a question about their own picture: Are you the same person today that you were at the moment captured in your photo. Students readily admit that their physical appearance and mental life have changed dramatically. They concede that they are not qualitatively identical today with the person in the photo, but most insist that that the adolescent they see in their selfie is numerically identical with the child in the photo. Childhood and adolescence are two stages in the life of one person, not two distinct persons that might bear a family resemblance.
What justification can be given for this conclusion? In other words, what persistence conditions are necessary and sufficient for (numerical) personal identity over time?
Discussion leads to three candidates for personal identity:
1) soul (same soul, same person)
2) body (same body, same person), and
3) psychological continuity (or, more narrowly, memory as the right glue to bind temporal stages to the same person).
Memento and the Memory Criterion for Personal Identity
In his 2000 film Memento, Christopher Nolan conducts a cinematic thought experiment that tests the memory criterion for personal identity. Leonard Shelby, the central character, suffers from a rare form of amnesia that prevents him from forming new memories that last for more than a few minutes. Leonard believes his personal identity is intact. He insists that memory is in any case unreliable and that he has forged stronger links between past and present episodes of his life through annotated polaroids, notes, and tattoos on his body. Knowing that Leonard’s memory will quickly fade, Teddy, a crooked cop who exploits Leonard’s condition, openly expresses his skepticism:
Teddy: You do not know who you are. Leonard: I’m Leonard Shelby. I’m from San Francisco. Teddy: That’s who you were.
Teddy later confronts Leonard with the inconvenient truth that even his remote links to the incident and his pre-incident life are unreliable. Leonard believes that his wife’s killer escaped. The mementos keep alive Leonard’s mission of avenging his wife’s murder. But Teddy hints that Leonard’s wife didn’t die in the attack and insists that Leonard already found and killed the “John G.” who broke into his home, attacked his wife, and stole his memory. Teddy, whose given name is John Gamel, says Leonard should “cheer up because there are plenty of John G.’s out there.” Leonard decides to make Teddy his John G. As he writes down Teddy’s license plate number, Leonard says to himself, “Do I lie to myself to give my life a sense of purpose. In your case, Teddy, yes I will.” The film begins with Leonard killing Teddy. It ends with him arriving at the tattoo parlor with Teddy’s license plate number. These crucial scenes suggest that even Leonard has a fleeting recognition that his mementos fail to secure personal identity. At the moment he writes down the license number, it appears that Leonard knowingly sends the message not to himself but to some future person occupying his body.
By moving backward in time, the film cleverly creates for the viewer the same experience of disorientation that torments Leonard. Because we don’t yet know what happened earlier, each scene is puzzling. Only when we use our own reliable memories to reconstruct the story do the seemingly disconnected fragments fit together. For example, we see Leonard sitting in a room holding an empty bottle. He thinks, “Funny, I don’t feel drunk.” In the next scene, we learn that Leonard is wielding the bottle as a weapon. The scene suggests that without historical context, even present moments can’t be experienced as meaningful.