What makes someone the same person over time? The most common suggestion for answering this question is explored by the movie, Dark City: memory. It investigates the idea of how identity and memory are linked. Does a change of memory mean a change of identity? Or is there something else that makes identity, like a soul?
The Operation of Memory
In Dark City, mysterious Strangers are erasing and replacing people’s memories—a feat accomplished by injecting chemicals into their brain with a syringe. In one scene, a lower-class man and his wife are knocked out, their house is improved, their clothes changed, and they’re injected with memories of being filthy rich. They wake, and the man brags to his wife about firing someone from his law firm. Is the rich man who awakes identical to the poor man who fell asleep?
Is it memory then? Maybe it’s the fact that you remember being your 8-year-old self that makes you numerically identical to your 8-year-old self. This suggestion was most famously made by John Locke, the 17th-century philosopher, who argues that:
… as far as this consciousness can be extended backwards to any past action or thought, so far reaches the identity of that person; it is the same self now it was then …
Now Locke seems to misuse the word “consciousness;” what Locke must have meant is “memory”—otherwise his argument makes no sense. In short, if A remembers being B, then A is B.
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The Flaw in Locke’s Logic
Locke’s critic, Thomas Reid, pointed out the most notable flaw in Locke’s theory:
[M]y remembrance [of an action] is the evidence I have that I am the identical person who did it. … But, to say that my remembrance that I did such a thing … makes me the person who did it, is … an absurdity … [I]t is to attribute to memory … a strange magical power of producing its object, though that object must have existed before the memory … which produced it.
Perhaps memory is something we can use to track identity, but that doesn’t mean it determines identity. Persons make memories, memories don’t make persons.
Murdoch in Dark City
Dark City seems to endorse this objection as well. The plot revolves around a man named Murdoch, who accidentally awoke before his new memories could be implanted. He wanders the city, trying to figure out who he is and what the Strangers are doing. In an effort to catch him, the Strangers inject one of their own, Mr. Hand, with Murdoch’s memories.
But, although it does allow him to predict Murdoch’s actions, no one thinks Mr. Hand is the same person as Murdoch. As in the movie, so too in real life: Implanting my childhood memories into your mind would not turn you into me. Memories belong to persons; persons don’t belong to memories.
This is a transcript from the video series Sci-Phi: Science Fiction as Philosophy. Watch it now, on The Great Courses Plus.
Is Soul the Answer?
Unfortunately, the answer to the question of identity that the movie suggests is not much better than Locke’s. According to Dr. Schreber in Dark City, what the Strangers are looking for is “the human soul”—what they think gives us our individuality—individuality being something the Stranger’s lack. This is why they are trading out memories in people. They think that if they can find what persists, in the midst of multiple memory swaps, they will have found the soul.
But “having the same soul” fails drastically as an answer to what preserves identity. Not only is the existence of the soul on extremely thin philosophic ice, but the continued existence of one’s soul could neither be necessary nor sufficient for the preservation of one’s personal identity. So even if the Strangers found the human soul, they would not have found the explanation for our individuality.
To see why, consider what the soul is supposed to be. According to the philosopher René Descartes, there are two types of substances: the material and the immaterial. Material substances can’t think; immaterial substances can. For Descartes a soul is a person; “a thing that thinks.”
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Souls are thought to be that which houses psychology—our thoughts, our decisions, our personality, our memories. With this in mind, let us see why having the same soul is not necessary for personal survival. Let us modify a thought experiment from Gottfried Leibniz to explain why.
Suppose you switch souls with George Lucas, the creator of Star Wars who works at Skywalker Ranch. His soul is now in your body, but has your psychology—and your soul is now in his body, but has his psychology. Have you thus switched identities? Are you now the creator of Star Wars?
No. Indeed, no one—including the two of you—would even know that anything had happened. The person in each body would remember always having been that person. But a difference that makes no difference, is no difference at all. So even though the substance that houses each person’s mentality is different, you’re still you and George is still George. It follows that having the same soul is not necessary for the preservation of personal identity; you could get a new one, but still be you.
Switching Psychologies, Retaining Souls
But suppose we retain the souls, but switch psychologies between you and George Lucas? Wouldn’t we say that you now work at Skywalker Ranch—since the person working there has all of your memories and personality—even though your soul is still back in your original body? It seems so, and thus having the same soul is not sufficient to preserve your personal identity either.
At the end of Dark City, Murdoch suggests that it is love that is the true location of identity. But philosophically even this is weak. After all, two different people can love the same person, and you can change who you love without ceasing to exist.
Common Questions about Personal Identity
John Locke, the 17th-century philosopher, suggested that memory makes identity. If you can remember being, say, an 8-year-old, then, Locke suggests, you and that younger self could be said to have the same identity.
In Dark City, the Strangers appear to be erasing and replacing people’s memories by injecting chemicals into their brain with a syringe.
According to Dr. Schreber, what the Strangers in Dark City are looking for is “the human soul”. This is why they are trading out memories in people. They think that if they can find what persists, in the midst of multiple memory swaps, they will have found the soul.