Dark City (1998) and Memento (2000) both illuminate an essential problem: if memory is flawed, can I know that I am me? In other words, memory is a central feature of personal identity; it’s a psychological criterion for asserting that what I call my self persists over time.

Memory is one of the key ways we string together past events, emotions, and thoughts, and tie them to our present. It’s a way of forming this entity we each call “me.” So what happens when memory is altered, as it is in Dark City, or almost entirely eliminated, as it is in Memento? Does the self fall apart as well?

In Dark City, John Murdoch (Rufus Sewell) awakens in a hotel bathtub with no memory of how he got there. He leaves the bathroom only to find a gruesome scene in the hotel room: a ritualistically murdered woman. All signs point to him as the killer. Not only does he not recognize the woman, he has he no memory of having killed her. Worse yet, he doesn’t even know who he is. In his search to uncover the truth about himself and the murder, he learns something horrifying: people’s memories have been altered for years to the point that it seems no credible memory for any single person is left.

Philosophers have long been interested in the role of memory in determining personal identity, or what one calls the self. Insofar as my memories are mine, there would seem to be some entity — my fundamental self — that is the subject that underlies them. On this view of the self, even if one’s memories have been replaced, or one cannot remember who one is, one can still feel intimately that there is an ‘I,’ or a very real what-it-is-to-be-me feeling. In the case of Dark City, Murdoch’s experiences in pursuing the truth, when strung together, create in him a sense of “self.”

Nevertheless, memory seems to be crucial, on some accounts, to answering the question, ‘What makes me persist as myself from one moment to the next?’ It rankles to suppose that Murdoch does not have access to his real life. Worse yet, if he is the murderer, but doesn’t remember it because different memories have been implanted in place of the ones connected to the killing, how can he be held to the same moral standard as, say, someone who murders and remembers doing it? After all, in the film, there is the strong suggestion that Murdoch is not the murdering type — at least not the Murdoch the audience knows. Whoever he might have been with other memories can’t be said to be him now. If he cannot remember his experiences, then how are they his?

The problem faced by Leonard Shelby (Guy Pearce), the main character in Memento, is almost the opposite of that which John Murdoch confronts in Dark City. Shelby cannot form new memories. He does retain memories of his past before an accident left him with anterograde amnesia, which means none of his present day memories last more than a few minutes before fading into nonexistence. When he’s distracted, he loses his train of thought, and so cannot remember what he was thinking only moments before.

Shelby’s predicament is complicated by the fact that his injury occurred when his wife was raped and murdered in their home. For some time, despite his condition, he has been on the hunt for his wife’s killer. His main methods of retaining clues he won’t remember are by taking Polaroids of people and places, making notes, and tattooing words and phrases on his body.

Complicating things for the audience is the fact that Memento is presented in reverse chronological order, so that the ending of one scene is the beginning of the one immediately preceding it. This forces the viewer to force the “correct,” chronological order on the story — something we know Shelby can’t do himself. Watching the scenes in the order presented puts the viewer into a state of confusion that must be something like what Shelby experiences. At the very least, it is disorienting.

As the film progresses, it becomes abundantly clear that Shelby’s anterograde amnesia is not his only, or worst, problem. Even his memories may be suspect. Intercut throughout the story are black and white scenes of Shelby’s previous life as an insurance investigator. One of his cases involved a man named Sammy Jankis, who had suffered amnesia after a car accident. Medical bills piled up since then, but Shelby believed Sammy’s condition to be mental, not physical, and so denies the claims.

Increasingly desperate, Sammy’s wife set out to get her husband’s memory back. She has him hide his food, hoping he’ll get hungry enough to remember where he put it. Finally, in utter despair, she asks him repeatedly, over the course of an hour, to give her insulin injections. He does. But was there really a Sammy Jankis? Could Leonard’s tattoo, “Remember Sammy Jankis” actually be a reminder about his own life? Could the memory of his wife’s murder really be a story he’s told himself to cope with having killed her?

Despite his deeply flawed condition, Leonard refuses to give up his quest. As he has it,

Memory’s not perfect. It’s not even that good. Ask the police, eyewitness testimony is unreliable. The cops don’t catch a killer by sitting around remembering stuff. They collect facts, make notes, draw conclusions. Facts, not memories: that’s how you investigate. I know, it’s what I used to do. Memory can change the shape of a room or the color of a car. It’s an interpretation, not a record. Memories can be changed or distorted and they’re irrelevant if you have the facts.

To be sure, the guy has a point. Whether we suffer from a severely limiting condition like Leonard’s, or you’re a “normal” person reporting what you’ve seen, you could get things wrong. That, in turn, could make you wonder about what you really know and who you really are. Memento forces us to think about these topics. As Leonard reminds us, they are essential to the human condition:

I have to believe in a world outside my own mind. I have to believe that my actions still have meaning, even if I can’t remember them. I have to believe that when my eyes are closed, the world’s still there. Do I believe the world’s still there? Is it still out there?...

The philosophical literature on personal identity and memory is vast. Among the first to tackle the question of memory’s relation to what we call a self was English philosopher, John Locke. More specifically, he argued that one’s continuity of consciousness makes it possible for you to say that you exist from one moment to the next as the same self. Memory is required for this awareness of continuity, since there are obvious gaps in consciousness, such as when you sleep. Memory allows you to string together yesterday with today, or this morning with this afternoon, or 10 minutes ago with now.

On Locke’s view, there is no discernible self we can call Leonard Shelby. On the other hand, if what makes you the same self over time is determined by physical continuity, we could say that Shelby is the same. After all, biologically, it looks like there is persistence of identity. Of course, there are considerable physical changes, both internally and externally. One can have an appendix removed, one can cut one’s hair. In Shelby’s case, there is the ever-expanding mural of tattoos. More troublesome, however, is the following possibility: if you are your body, rather than some feature or features of your mind, then, should the two ever be separated, “you” would stay with your body. That just sounds weird.

Another significant view is that personal identity is not something real — at least, there’s no entity that we can call a self. This view is common both to certain Eastern and Western traditions, and continues to have a fair number of adherents. So, the answer to the question, ‘What am I?’ is not going to include an enduring, simple thing, like a soul or an immutable self. On one version of this view, articulated by Scottish philosopher, David Hume and brought into contemporary popularity by thinkers like Derek Parfit,[1] there is no fundamental “me” that survives the various changes “I” go through. Instead, there is a collection of psychological states that undergo revisions, and so far as these are continuous, there is a “me.” On this view, Leonard Shelby is not continuous with the various Leonard Shelbys after the brain injury, but each one is apparently continuous with the original Leonard — the one before the accident.

For someone who agrees with Parfit, however, this is not a disaster. That’s because memory is not the most significant psychological feature of the collection or bundle of features that make up Leonard Shelby. Imagine, for example, that Shelby enters a replicator machine, which is supposed to copy him in his entirety, annihilating each particle as it is duplicated. His Replica is then supposed to be sent to Mars. Unfortunately, there’s a glitch in the machine, and Shelby isn’t annihilated, but his Replica does go to Mars. The original Shelby will be dead shortly, as soon as the machine is fixed, but for several minutes, both he and his Replica exist. Two questions emerge: 1) Which one is Leonard Shelby? 2) Does the fact that the Replica has all of Earth Shelby’s memories matter to Earth Shelby? After all, he’s going to die! It’s his Replica that will live.

In a sense, this is just what Shelby’s experiences in Memento are like. As we know, every few minutes he loses his short term. It might seem terribly traumatic at first, since it feels like an annihilation of his self. But as we’ve seen from Parfit’s Replica thought experiment, continuing memory for Shelby’s Replica doesn’t make Earth Shelby feel any better about his impending death. (The same could be said about the Replica, who could be disturbed that someone else was claiming to be him.) As Parfit points out,

The fact that my Replica has all my memories, and is in every other way just like me psychologically, that isn’t enough to make him me. And that’s brought out…by the fact that, if they can make one Replica with the information, they can make 100 all at the same time. Now, I wouldn’t be 100 different people who each seem to remember living my life. I wouldn’t even be two of them, but 100 is clearly too much. So, memory doesn’t, in that sense, guarantee identity.[2]

So where does all this leave poor Leonard Shelby and John Murdoch? Is there any hope for them to be themselves given what Parfit argues? In a word, yes, but it’s not quite what you would ordinarily think. In fact, if memory is unreliable, it could very well be a relief to say that you are not identical with your memories. Leonard and John don’t have to ask if the future self will be identical to the current self, at least not so far as memory goes. They also don’t need, on Parfit’s view, anyway, to wonder if the self is some sort of indivisible, enduring entity, like a soul. This means, then, that they need to think of themselves as nothing more than, that is, no “I” over and above closely connected thoughts and experiences.

[1] “Divided Minds and the Nature of Persons,” in Mindwaves: Thoughts on Intelligence, Identity, and Consciousness, edited by Colin Blakemore and Susan Greenfield. Blackwell, 1989.

[2] https://www.youtube.com/watch?v=uS-46k0ncIs, minute marker 8.46.