I'd classify the film as speculative fiction (one could have called it "science fiction", only this term has been hijacked to mean action movies with dark metallic corridors lit by strips of neon, 1-piece jumpsuits, futuristic gadgets and lots of blinking lights). Basically, the story is this: neurotic boy (Jim Carrey, who's not at all the buffoon he's best known as) meets psycho hairdye girl (Kate Winslet, looking like too many cute-but-insane punk/goth/raver chicks you've probably met), and they hook up; then, sometime later, their relationship falls apart, and she goes to a clinic to have all memories of him eradicated from her mind. He runs into her, she doesn't recognise him then goes to the same clinic to do the same. Only as it's happening, he suddenly has a change of heart and races around the landscape of his mind, trying to save the memories of her from the erasure technicians. There's more to the story, such as one of the technicians (played by Elijah "Frodo" Wood, only looking like a member of a nu-metal boy-band) hitting on a way of using attractive female patients' erased memories to hook up with them, and the issue of whether erasing all memories of a failed relationship would be mostly good or mostly bad.
The gist of the film seems to be that erasing a memory is not the same as preventing an event from recurring; in the film, characters whose memories of their relationships with each other have been erased hook up again and repeat their connections. If you're a sentimentalist or wish to consider the film as a romantic comedy, it could be about the power of destiny and true love and soulmates being brought together by powerful forces beyond their control, like the angels people talk about on American daytime TV talk shows or something. If you're more of a skeptic or a cynic, it's more about one being destined to repeat mistakes if one doesn't remember them. On a deeper level, I thought it was about how the dynamic workings of the human mind are composed not so much of things (such as memories of moments and people) as of processes; you can lose your memories, but if you're still the same person you were before (and if you have lost learnings since, you may be more likely to be), the internal processes of your mind will guide you into repeating what you have forgotten, or at least riffing off it. (Maybe if one was to start a real-life Lacuna Inc., one would combine aversion conditioning with memory erasure, to make the patients avoid their problem exes, but I digress.)
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