Harry Potter and the Methods of Rationality

people now thought the Daily Prophet had just made the whole thing up for unguessable reasons, and the Quibbler had helpfully twisted the knife deeper with the next day's headline, HARRY POTTER SECRETLY BETROTHED TO LUNA LOVEGOOD.

Whoever they'd hired would tell them after the statute of limitations expired, they desperately hoped. But meanwhile it was awful, they'd pulled their greatest prank ever, maybe the greatest prank in the history of pranking, and they couldn't remember how. It was crazy, they'd been able to think of a way the first time, so why couldn't they see it now after knowing everything they'd done?

Their only consolation was that Harry didn't know they didn't know.

Not even Mum had questioned them about it, despite the obvious Weasley connection. Whatever had been done, it was far out of the reach of any Hogwarts student... except possibly one, who, if certain rumors were true, might have done it by snapping his fingers. Harry had been questioned under Veritaserum, he'd told them... with Dumbledore present and giving the Aurors scary looks. The Aurors had asked just enough to determine that Harry hadn't pulled the prank himself or disappeared anyone, and then gotten the heck out of Hogwarts.

Fred and George had wondered whether to feel insulted about Harry Potter being questioned by the Aurors for their prank, but the look on Harry's face, probably for exactly the same reason, made everything worth it.

Unsurprisingly, Rita Skeeter and the editor of the Daily Prophet had both vanished and were probably in another country by now. They would've liked to be able to tell their family about that part. Dad would have congratulated them, they thought, after Mum had finished killing them and Ginny had burned the remains.

But everything was still all right, they'd tell Dad someday, and meanwhile...

...meanwhile Dumbledore had happened to sneeze while passing them in the hallway, and a small package had accidentally dropped out of his pockets, and inside had been two matched wardbreaker's monocles of incredible quality. The Weasley twins had tested their new monocles on the 'forbidden' third-floor corridor, making a quick trip to the magic mirror and back, and they hadn't been able to see all the detection webs clearly, but the monocles had shown a lot more than they'd seen the first time.

Of course they would have to be very careful never to get caught with the monocles in their possession, or they would end up in the Headmaster's office getting a stern lecture and maybe even threats of expulsion.

It was good to know that not everyone who got Sorted into Gryffindor grew up to be Professor McGonagall.

Harry was in a white room, windowless, featureless, sitting before a desk, facing an expressionless man in formal robes of solid black.

The room was screened against detection, and the man had performed exactly twenty-seven spells before saying so much as 'Hello, Mr. Potter.'

It was oddly appropriate that the man in black was about to try reading Harry's mind.

'Prepare yourself,' the man said tonelessly.

A human mind, Harry's Occlumency book had said, was only exposed to a Legilimens along certain surfaces. If you failed to defend your surfaces, the Legilimens would go through and be able to access any part of you which their own mind was able to comprehend...

...which tended not to be much. Human minds, it seemed, were hard for humans to understand on any level but the shallowest. Harry had wondered if knowing lots of cognitive science could make him an incredibly powerful Legilimens, but repeated experience had finally driven into him the lesson that he needed to get a little less excited in his anticipations about this sort of thing. It wasn't as if any cognitive scientist understood humans well enough to make one.

To learn the counter, Occlumency, the first step was to imagine yourself to be a different person, pretending it as thoroughly as you could, immersing yourself entirely in that alternate persona. You wouldn't always have to do that, but in the beginning, it was how you learned where your surfaces were. The Legilimens would try to read you, and you would feel it happening if you paid close enough attention, you would sense them trying to enter. And your job was to make sure that they always touched your imaginary persona and not the real one.

When you were good enough at that, you could imagine being a very simple sort of person, pretend to be a rock, and make a habit of leaving the pretense in place where all your surfaces were. That was a standard Occlumency barrier. Pretending to be a rock was hard to learn, but easy to do afterward, and the exposed surface of a mind was much shallower than its interior, so with enough practice you could keep it up as a background habit.

Or if you were a perfect Occlumens, you could race ahead of any probes, answering queries as fast as they were asked, so that the Legilimens would enter through your surfaces and see a mind indistinguishable from whoever you were pretending to be.

Even the best Legilimens could be fooled that way. If a perfect Occlumens claimed they were dropping their Occlumency barriers, there was no way to know if they were lying. Worse, you might not know you were dealing with a perfect Occlumens. They were rare, but the fact that they existed meant you couldn't trust Legilimency on anyone.

It was a sad commentary on how little human beings understood each other, how little any wizard comprehended the depths lying beneath the mind's surface, that you could fool the best human telepaths by pretending to be someone else.

But then human beings only understood each other in the first place by pretending. You didn't make predictions about people by modeling the hundred trillion synapses in their brain as separate objects. Ask the best social manipulator on Earth to build you an Artificial Intelligence from scratch, and they'd just give you a dumb look. You predicted people by telling your brain to act like theirs. You put yourself in their place. If you wanted to know what an angry person would do, you activated your own brain's anger circuitry, and whatever that circuitry output, that was your prediction. What did the neural circuitry for anger actually look like inside? Who knew? The best social manipulator on Earth might not know what neurons were, and neither might the best Legilimens.

Anything a Legilimens could understand, an Occlumens could pretend to be. It was the same trick either way - probably implemented by the same neural circuitry in both cases, a single set of control circuits for reconfiguring your own brain to act as a model of