And what's the thematic point of the Sammy story in the first place? Is it a hint that Leonard's condition may not be real? As Leonard tells the tale, the crucial point is whether Sammy had suffered physical brain damage or if his affliction was somehow psychological. In the end, has Nolan taken refuge in a new version of that hoary thriller cliché, "It was all a dream"? Are the confusing final scenes just evidence of Leonard's brain synapses misfiring as he sits in the asylum?

On the other hand, what's the point of a good movie about memory if you don't leave a few things up for grabs? As Leonard himself tells Teddy fairly early on, "Memory's unreliable ... Memory's not perfect. It's not even that good. Ask the police; eyewitness testimony is unreliable ... 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." This is the very heart of the film. "Memento" is a movie largely about memory -- the ways in which it defines identity, how it's necessary to determine moral behavior and yet how terribly unreliable it is, despite its crucial role in our experience of the world.

In its own weird way, it's also a tribute to grief. Grief is an emotion largely based on memory, of course. It is one of "Memento's" brilliant tangential themes that relief from grief is dependent on memory as well -- and that is one of the chief hells our unfathomable hero is subjected to. "How am I supposed to heal if I can't feel time?" Leonard asks.

Still, even after so many viewings, after reading the script and discussing the film for months, I haven't been able to come up with the "truth" about what transpired prior to the film's action. Every explanation seems to involve some breach of the apparent "rules" of Leonard's disability -- not merely the rules as he explains them, but the rules as we witness them operating throughout most of the film.

The scene of him and his wife in bed, the triumphant tattoo on his breast, can't be a flashback. We've seen already that he doesn't have the tattoo, so he can't have had it in the past. How can he remember lying in bed with his living wife, with the tattoo "John G. raped and killed my wife" visible on his chest? It has to be a fantasy, which would make sense in the context. He thinks he has just avenged her (or has just set in motion a plan to avenge her). He's visualizing his own sense of satisfaction and peace.

Did Sammy kill his wife with insulin? Or did Leonard? For Leonard to have killed his wife and then have transferred the story onto Sammy (as Teddy claims) would require that Leonard remember an event that happened after his accident. Yes, Leonard has a quick memory flash of injecting his wife, but it's followed by a repetition of an earlier version of the memory, where he was merely pinching her. So, of course, the injection memory is just the other memory distorted by Teddy's suggestion.

Except, several hours later in the chronology -- which is to say earlier in the film -- Leonard, sitting at Natalie's house, has another momentary memory flash of preparing the injection. (It appears to be the exact same shot as before.) Even if the image was a false one, influenced by what Teddy said, how can Leonard still remember it hours later?

Who ends up in the mental hospital? Well, Leonard tells us that Sammy ends up there. But Teddy tells us that Leonard's nuts, and then there's that flash in which we see Leonard himself there. And Jonathan Nolan's authorized Web site -- which apparently counts as part of the official canon -- is unambiguous about Leonard being an escapee from an asylum.

Is there an answer? I don't know. Christopher Nolan claims there is one. In an article in New Times Los Angeles on March 15, Scott Timberg writes: "Nolan, for his part, won't tell. When asked about the film's outcome, he goes on about ambiguity and subjectivity, but insists he knows the movie's Truth -- who's good, who's bad, who can be trusted and who can't -- and insists that close viewing will reveal all."

But, at this point, I no longer believe him. The only way to reconcile everything is to assume huge inconsistencies in the nature of Leonard's disorder. In fact, in real life, such inconsistencies apparently exist, if Oliver Sacks is to be believed. But to build the plot around them without giving us some hints seems like dirty pool.

Still, even if it turns out that Nolan has cheated like a two-bit grifter in fashioning his story, "Memento" remains an extraordinary achievement. Not only has he devised a film that challenges its audience, demanding the sort of attention and thought that Hollywood would never ask of viewers, but he has used his cleverness to stir up questions and feelings about the most basic issues of how we experience reality. In addition to being a puzzle, "Memento" is a philosophical tragedy that considers issues the makers of "Pearl Harbor" could never dream of.

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