Harry Potter and the Methods of Rationality

by Eliezer Yudkowsky

  Hermione raised her wand again, pointed it at the eraser.

  For a moment anger crossed Harry's face, but he didn't make any move to stop her.

  "Finite Incantatem," said Hermione. "Check with Professor McGonagall before you try it again."

  Harry nodded, though his face was still a bit tight.

  "And we still have to stop," said Hermione.

  "Why?" said Harry. "Don't you see what this means, Hermione? Wizards don't know everything! There's too few of them, even fewer who know any science, they haven't exhausted the low-hanging fruit -"

  "It's not safe," Hermione said. "If we can find out new things it's even less safe! We're too young! We made one big mistake already, next time we could just die!"

  Then Hermione flinched.

  Harry looked away from her, and started taking slow, deep breaths.

  "Please don't try to do it alone, Harry," Hermione said, her voice trembling. "Please."

  Please don't make me have to decide whether to tell Professor Flitwick.

  There was a long pause.

  "So you want us to study," Harry said. She could tell he was trying to keep the anger out of his voice. "Just study."

  Hermione wasn't sure if she should say anything, but... "Like you studied, um, timeless physics, right?"

  Harry looked back at her.

  "That thing you did," Hermione said, her voice tentative, "it wasn't because of our experiments, right? You could do it because you'd read lots of books."

  Harry opened his mouth, and then he shut it again. There was a frustrated look on his face.

  "All right," Harry said. "How about this. We study, and if I think of anything that seems really worth trying, we'll try it after I ask a professor."

  "Okay," Hermione said. She didn't fall over with relief, but only because she was already sitting down.

  "Shall we get lunch?" Harry said cautiously.

  Hermione nodded. Yes. Lunch sounded good. For real, this time.

  She carefully began to push herself off the stone floor, wincing as her body screamed at her -

  Harry pointed his wand at her and said "Wingardium Leviosa."

  Hermione blinked as the huge weight on her legs diminished to something bearable.

  A smile quirked across Harry's face. "You can lift something without being able to Hover it completely," he said. "Remember that experiment?"

  Hermione smiled back helplessly, although she thought she ought to still be angry.

  And she started walking back toward the Great Hall, feeling remarkably and wonderfully light on her feet, as Harry carefully kept his wand trained on her.

  He only managed to keep it up for five minutes, but it was the thought that counted.

  Minerva looked at Dumbledore.

  Dumbledore gazed back inquiringly at her. "Did you understand any of that?" the Headmaster said, sounding bemused.

  It had been the most complete and utter gibberish that Minerva could ever remember hearing. She was feeling a bit embarrassed about having summoned the Headmaster to hear it, but she'd been given explicit instructions.

  "I'm afraid not," Professor McGonagall said primly.

  "So," Dumbledore said. The silver beard swung away from her, the old wizard's twinkling gaze looked elsewhere once more. "You suspect you might be able to do something that other wizards can't do, something we think is impossible."

  The three of them stood within the Headmaster's private Transfiguration workroom, where the shining phoenix of Dumbledore's Patronus had told her to bring Harry, moments after her own Patronus had reached him. Light shone down through the skylights and illuminated the great seven-pointed alchemical diagram drawn in the center of the circular room, showing it to be a little dusty, which saddened Minerva. Transfiguration research was one of Dumbledore's great enjoyments, and she'd known how pressed for time he'd been lately, but not that he was this pressed.

  And now Harry Potter was going to waste even more of the Headmaster's time. But she certainly couldn't blame Harry for that. He'd done the proper thing in coming to her to say that he'd had an idea for doing something in Transfiguration that was currently believed to be impossible, and she herself had done exactly what she'd been told to do: she'd ordered Harry to be quiet and not discuss anything with her until she had consulted the Headmaster and they'd finished moving to a secure location.

  If Harry had started out by saying what specifically he thought he could do, she wouldn't have bothered.

  "Look, I know it's hard to explain," Harry said, sounding a little embarrassed. "What it adds up to is that what you believe conflicts with what scientists believe, in a case where I'd genuinely expect scientists to know more than wizards."

  Minerva would have sighed out loud, if Dumbledore hadn't seemed to be taking the whole thing very seriously.

  Harry's idea stemmed from simple ignorance, nothing more. If you changed half of a metal ball into glass, the whole ball had a different Form. To change the part was to change the whole, and that meant removing the whole Form and replacing it with a different one. What would it even mean to Transfigure only half of a metal ball? That the metal ball as a whole had the same Form as before, but half that ball now had a different Form?

  "Mr. Potter," said Professor McGonagall, "what you want to do isn't just impossible, it's illogical. If you change half of something, you did change the whole."

  "Indeed," said Dumbledore. "But Harry is the hero, so he may be able to do things that are logically impossible."

  Minerva would have rolled her eyes, if she hadn't gone numb a long time ago.

  "Supposing it was possible," said Dumbledore, "can you think of any reason why the results would differ in any way from ordinary Transfiguration?"

  Minerva frowned. The fact that the concept was literally unimaginable was presenting her with some difficulty, but she tried to take it at face value. A Transfiguration imposed on only half of a metal ball...

  "Strange things happening at the interface?" said Minerva. "But that should be no different than Transfiguring the object as a whole, into a Form with two different parts..."

  Dumbledore nodded. "That is my own thought as well. And Harry, if your theory is correct, it implies that what you want to do is exactly like any other Transfiguration, only applied to a part of the subject rather than the whole? No changes at all?"

  "Yes," Harry said firmly. "That's the whole point."

  Dumbledore looked at her again. "Minerva, can you think of any reason whatsoever why that would be dangerous?"

  "No," said Minerva, after she had finished searching through her memory.

  "Likewise myself," said the Headmaster. "All right, then, since this ought to be exactly analogous to ordinary Transfiguration in all respects, and since we cannot think of any reason whatsoever why it would be dangerous, I think that the second degree of caution will suffice."

  Minerva was surprised, but she didn't object. Dumbledore was by far her senior in Transfiguration, and he had tried literally thousands of new Transfigurations without ever choosing a degree of caution that was too low. He had used Transfiguration in combat and he was still alive. If the Headmaster thought the second degree was enough, it was enough.

  That Harry was certainly going to fail was, of course, completely irrelevant.

  The two of them started setting up the wards and detection webs. The most important web was the one that checked to make sure no Transfigured material had entered the air. Harry would be enclosed in a separate shell of force with its own air supply just to be certain, only his wand allowed to leave the shield, and the interface tight. They were inside Hogwarts so they couldn't automatically Apparate out any material that showed signs of spontaneous combustion, but they could launch it out a skylight almost as fast, the windows all folded outward for exactly that reason. Harry himself would go out a different skylight at the first sign of trouble.

  Harry watched them working, his face looking a little frightened.

  "Don't worry," said Prof
essor McGonagall in the middle of her running description, "this almost certainly won't be necessary, Mr. Potter. If we expected anything to go wrong you would not be allowed to try. It's just ordinary precautions for any Transfiguration no one has ever tried before."

  Harry swallowed and nodded.

  And a few minutes later, Harry was strapped into the safety chair and resting his wand against a metal ball - one that, based on his current test scores, should have been too large for him to Transfigure in less than thirty minutes.

  And a few minutes after that, Minerva was leaning against the wall, feeling faint.

  There was a small patch of glass on the ball where Harry's wand had rested.

  Harry didn't say I told you so, but the smug look on his sweating face said it for him.

  Dumbledore was casting analytic Charms on the ball, looking more and more intrigued by the moment. Thirty years had melted off his face.

  "Fascinating," said Dumbledore. "It's exactly as he claimed. He simply Transfigured a part of the subject without Transfiguring the whole. You say it's really just a conceptual limitation, Harry?"

  "Yes," Harry said, "but a deep one, just knowing it had to be a conceptual limitation wasn't enough. I had to suppress the part of my mind that was making the error and think instead about the underlying reality that scientists figured out."

  "Truly fascinating," Dumbledore said. "I take it that for any other wizard to do the same would require months of study if they could do it at all? And may I ask you to partially Transfigure some other subjects?"

  "Probably yes and of course," Harry said.

  Half an hour later, Minerva was feeling equally bewildered, but considerably reassured about the safety issues.

  It was the same, aside from being logically impossible.

  "I believe that's enough, Headmaster," Minerva said finally. "I suspect partial Transfiguration is more tiring than the ordinary sort."

  "Getting less so with practice," said the exhausted and pale boy, voice unsteady, "but yeah, you've got that right."

  The process of extracting Harry from the wards took another minute, and then Minerva escorted him to a much more comfortable chair, and Dumbledore produced an ice-cream soda.

  "Congratulations, Mr. Potter!" said Professor McGonagall, and meant it. She would have bet almost anything against that working.

  "Congratulations indeed," said Dumbledore. "Even I did not make any original discoveries in Transfiguration before the age of fourteen. Not since the day of Dorotea Senjak has any genius flowered so early."

  "Thanks," Harry said, sounding a little surprised.

  "Nonetheless," Dumbledore said thoughtfully, "I think it would be most wise to keep this happy event a secret, at least for now. Harry, did you discuss your idea with any other person before you spoke to Professor McGonagall?"

  There was silence.

  "Um..." Harry said. "I don't want to turn anyone over to the Inquisition, but I did tell one other student -"

  The word almost exploded from Professor McGonagall's lips. "What? You discussed a completely novel form of Transfiguration with a student before consulting a recognized authority? Do you have any idea how irresponsible that was?"

  "I'm sorry," said Harry. "I didn't realize."

  The boy looked appropriately frightened, and Minerva felt something inside her relax. At least Harry understood how foolish he'd been.

  "You must swear Miss Granger to secrecy," Dumbledore said gravely. "And do not tell anyone else unless there is an extremely good reason for it, and they too have sworn."

  "Ah... why?" Harry said.

  Minerva was wondering the same thing. Once again the Headmaster was thinking too far ahead for her to keep up.

  "Because you can do something that no one else will believe you can do," Dumbledore said. "Something completely unexpected. It may prove to be your critical advantage, Harry, and we must preserve it. Please, trust me in this."

  Professor McGonagall nodded, her firm face showing nothing of her inner confusion. "Please do, Mr. Potter," she said.

  "All right..." Harry said slowly.

  "Once we have finished examining your materials," Dumbledore added, "you may practice partial Transfiguration, on glass to steel and steel to glass only, with Miss Granger to act as your spotter. Naturally, if either of you suspect any symptom of any form of Transfiguration sickness, inform a professor at once."

  Just before Harry left the workroom, with his hand on the doorhandle, the boy turned back and said, "As long as we're here, have either of you noticed anything different about Professor Snape?"

  "Different?" said the Headmaster.

  Minerva didn't let her wry smile show on her face. Of course the boy was apprehensive about the 'evil Potions Master', since he had no way of knowing why Severus was to be trusted. It would have been odd to say the least, explaining to Harry that Severus was still in love with his mother.

  "I mean, has his behavior changed recently in any way?" said Harry.

  "Not that I have seen..." the Headmaster said slowly. "Why do you ask?"

  Harry shook his head. "I don't want to prejudice your own observations by saying. Just keep an eye out, maybe?"

  That sent a quiver of unease through Minerva in a way that no outright accusation of Severus could have.

  Harry bowed to both of them respectfully, and took his leave.

  "Albus," Minerva said after the boy had gone, "how did you know to take Harry seriously? I would have thought his idea merely impossible!"

  The old wizard's face turned grave. "The same reason it must be kept secret, Minerva. The same reason I told you to come to me, if Harry made any such claim. Because it is a power that Voldemort knows not."

  The words took a few seconds to sink in.

  And then the cold shiver went down her spine, as it always did when she remembered.

  It had started out as an ordinary job interview, Sybill Trelawney applying for the position of Professor of Divination.

  THE ONE WITH THE POWER TO VANQUISH THE DARK LORD APPROACHES,

  BORN TO THOSE WHO HAVE THRICE DEFIED HIM,

  BORN AS THE SEVENTH MONTH DIES,

  AND THE DARK LORD WILL MARK HIM AS HIS EQUAL,

  BUT HE WILL HAVE POWER THE DARK LORD KNOWS NOT,

  AND EITHER MUST DESTROY ALL BUT A REMNANT OF THE OTHER,

  FOR THOSE TWO DIFFERENT SPIRITS CANNOT EXIST IN THE SAME WORLD.

  Those dreadful words, spoken in that terrible booming voice, didn't seem to fit something like partial Transfiguration.

  "Perhaps not, then," Dumbledore said after Minerva tried to explain. "I confess I had been hoping for something that would help in finding Voldemort's horcrux, wherever he may have hidden it. But..." The old wizard shrugged. "Prophecies are tricky things, Minerva, and it is best to take no chances. The smallest thing may prove decisive if it remains unexpected."

  "And what do you suppose he meant about Severus?" said Minerva.

  "There I have no idea," sighed Dumbledore. "Unless Harry is making a move against Severus, and thought that an open question might be taken seriously where a direct allegation would be dismissed. And if that was indeed what happened, Harry correctly reasoned that I would not trust that it was so. Let us simply keep watch, without prejudice, as he asks."

  Aftermath, 1:

  "Um, Hermione?" Harry said in a very small voice. "I think I owe you a really, really, really big apology."

  Aftermath, 2:

  Alissa Cornfoot's eyes were slightly glazed as she gazed upon the Potions Master giving her class a stern lecture, holding up a tiny bronze bean and saying something about screaming puddles of human flesh. Ever since the start of this year she'd been having trouble listening in Potions. She kept staring at their awful, mean, greasy professor and fantasizing about special detentions. There was probably something really wrong with her but she just couldn't seem to stop doing it -

  "Ow!" Alissa said then.

  Snape had just flicked the bronze bean unerringly at Alissa
's forehead.

  "Miss Cornfoot," said the Potions Master, his voice cutting, "this is a delicate potion and if you cannot pay attention you will hurt your classmates, not just yourself. See me after class."

  The last four words didn't help her any, but she tried harder, and managed to get through the day without melting anyone.

  After class, Alissa approached the desk. Part of her wanted to stand there meekly with her face abashed and her hands clasped penitently behind her back, just in case, but some quiet instinct told her this might be a bad idea. So instead she just stood there with her face neutral, in a posture that was very proper for a young lady, and said, "Professor?"

  "Miss Cornfoot," Snape said without looking up from the sheets he was grading, "I do not return your affections, I begin to find your stares disturbing, and you will restrain your eyes henceforth. Is that quite clear?"

  "Yes," said Alissa in a strangled squeak, and Snape dismissed her, and she fled the classroom with her cheeks flaming like molten lava.

  Chapter 29: Egocentric Bias

  Unfortunately, no one can be told who J. K. Rowling is. You have to see her for yourself.

  Science disclaimers: Luosha points out that the theory of empathy in Ch. 27 (you use your own brain to simulate others) isn't quite a known scientific fact. The evidence so far points in that direction, but we haven't analyzed the brain circuitry and proven it. Similarly, timeless formulations of quantum mechanics (alluded to in Ch. 28) are so elegant that I'd be shocked to find the final theory had time in it, but they're not established yet either.

  There'd been a sinking feeling in Hermione's stomach lately, every time she heard the other students talking about her and Harry. She'd been in a shower stall this morning when she'd overheard a conversation between Morag and Padma that had been the last straw piled on top of quite a lot of other straws.

  She was starting to think that getting involved in a rivalry with Harry Potter had been a terrible mistake.