Harry Potter and the Methods of Rationality

Padma stared down at her plate. She was glad the Sorting Hat hadn't offered her Hufflepuff. If she'd been Sorted into Hufflepuff it would probably have been much more painful, trying to decide where her divided loyalties lay...

She blinked and realized that her vision had gotten blurry again, and raised a trembling hand to wipe once more at her eyes.

Morag MacDougal snorted so loudly it was audible even amid the pandemonium of lunch, and said in a loud voice, "I bet Granger cheated in her battle yesterday, I bet that's why Malfoy challenged her -"

"All of you SHUT UP!" roared Harry Potter, as he hit the table with his fists so hard that plates rattled all the way along it.

At any other time it would have gotten Professors reprimanding him, this time it just got a few nearby students to look.

"I'd wanted to eat lunch," Harry Potter said, "and then get back to investigating, so I wasn't going to talk. But you're all being silly, and when the truth comes out you're going to regret what you said about innocent people. Draco didn't do anything, Hermione didn't do anything, they were both False-Memory-Charmed!" Harry Potter's voice had been rising on the last words. "How is that not BLOODY OBVIOUS?"

"You think we'll believe that?" Kevin Entwhistle yelled right back at him. "That's what everyone says! 'I didn't do it, it was all just a False Memory Charm!' You think we're stupid?"

And Morag nodded right along with him, with a condescending look.

The look that came over Harry Potter's face then made Padma flinch.

"I see," Harry Potter said, it wasn't a shout so Padma had to strain to hear it. "Professor Quirrell isn't here to explain to me how stupid people are, but I bet this time I can get it on my own. People do something dumb and get caught and are given Veritaserum. Not romantic master criminals, because they wouldn't get caught, they would have learned Occlumency. Sad, pathetic, incompetent criminals get caught, and confess under Veritaserum, and they're desperate to stay out of Azkaban so they say they were False-Memory-Charmed. Right? So your brain, by sheer Pavlovian association, links the idea of False Memory Charms to pathetic criminals with unbelievable excuses. You don't have to consider the specific details, your brain just pattern-matches the hypothesis into a bucket of things you don't believe, and you're done. Just like my father thought that magical hypotheses could never be believed, because he'd heard so many stupid people talking about magic. Believing a hypothesis that involves False Memory Charms is low-status."

"What are you blithering about?" said Morag, looking down her nose at the Boy-Who-Lived.

"You think we'd believe anything you say?" yelled a slightly older-looking Ravenclaw witch who Padma didn't recognize. "When you turned Granger Dark?"

"And I'm not going to complain," Harry Potter said in an eerily calm voice, "about wizards not having any logic and believing the craziest things. Because I said that to Professor Quirrell once, and he just gave me this look and said that if I wasn't blinded by my upbringing I could think of a hundred more ridiculous things that lots of Muggles believe. What you're all doing is very human and very normal and doesn't make you unusually bad people, so I'm not going to complain." The Boy-Who-Lived rose up from his bench. "I'll see you all later."

And Harry Potter walked away from them, walked away from all of them.

"You're not thinking he's right, are you?" said Su Li from beside her, in a tone which made it clear what she thought.

"I -" said Padma. Her words seemed to be caught in her throat, her thoughts seemed to be caught in her head. "I - I mean - I -"

If you think hard enough you can do the impossible.

(It had always been an article of faith with Harry. There'd been a time when he'd acknowledged the laws of physics as ultimate limitations, and now he suspected there were no true limits at all.)

If you think fast enough you can sometimes do the impossible quickly...

...sometimes.

Only sometimes.

Not always.

Not reliably.

The Boy-Who-Lived stared around the trophy room, surrounded by awards and cups and plates and shields and statues and medals kept behind thousands, perhaps tens of thousands, of crystal glass displays. For as many centuries as Hogwarts had existed, this room had been accumulating details. A week, a month, maybe even a year, wouldn't have sufficed to take the 'examine' option on every item in the room. With Professor Flitwick gone, Harry had asked Professor Vector if there was any way to detect damage to the wards around the crystal cases, verify the residue that a real duel should have left behind. Harry had raced through the Hogwarts library looking for spells to tell the difference between old fingerprints and new fingerprints, or to detect lingering exhalations in a room. And all those attempts at playing detective had failed.