Harry Potter and the Methods of Rationality

by Eliezer Yudkowsky

  And the two of them walked on, in their tiny sphere of silence and isolation, through the brilliant and bustling crowds; and if you looked carefully, you would see that where they went, leafy boughs faded, and flowers withered, and children's toys that played cheerful bells changed to lower and more ominous notes.

  Harry did notice, but he didn't say anything, just smiled a little to himself.

  Everyone had their own way of celebrating the holidays, and the Grinch was as much a part of Christmas as Santa.

  Chapter 33: Coordination Problems, Pt 1

  I just recite to myself, over and over, until I can choose sleep: It all adds up to J. K. Rowling.

  The version of decision theory used in this chapter is not the academically dominant one. It's based on something called "timeless decision theory" that's under development by (among others) Gary Drescher, Wei Dai, Vladimir Nesov, and, well... (coughs a few times) me.

  The terrifying part was how fast the whole thing had spiraled out of control.

  "Albus," Minerva said, not even trying to keep the worry out of her voice as the two of them entered the Great Hall, "something has to be done."

  The atmosphere at Hogwarts before Yuletide was usually bright and cheerful. The Great Hall had already been decorated in green and red, after a Slytherin and a Gryffindor whose Yule wedding had become a symbol of friendship transcending Houses and allegiances, a tradition almost as ancient as Hogwarts itself and which had even spread to Muggle countries.

  Now the students eating dinner were glancing nervously over their shoulders, or sending vicious glares at other tables, or at some tables arguing heatedly. You could have described the atmosphere as tense, perhaps, but the phrase coming to Minerva's mind was fifth degree of caution.

  Take a school, into four Houses divided...

  Now into each year, add three armies at war.

  And the partisanship of Dragon and Sunshine and Chaos had spread beyond the first-years; they had become the armies for those who had no armies. Students were wearing armbands with insignia of fire or smile or upraised hand, and hexing each other in the corridors. All three first-year generals had told them to stop - even Draco Malfoy had heard her out and then nodded grimly - but their supposed followers hadn't listened.

  Dumbledore gazed out at the tables with a distant look. "In every city," the old wizard quoted softly,"the population has been divided for a long time past into the Blue and the Green factions... And they fight against their opponents knowing not for what end they imperil themselves... So there grows up in them against their fellow men a hostility which has no cause, and at no time does it cease or disappear, for it gives place neither to the ties of marriage nor of relationship nor of friendship, and the case is the same even though those who differ with respect to these colours be brothers or any other kin. I, for my part, am unable to call this anything except a disease of the soul..."

  "I'm sorry," said Minerva, "I don't -"

  "Procopius," said Dumbledore. "They took their chariot-racing very seriously, in the Roman Empire. Yes, Minerva, I agree that something must be done."

  "Soon," Minerva said, her voice lowering even further. "Albus, I think it must be done before Saturday."

  On Sunday, most students would leave Hogwarts to stay the holiday with their families; Saturday, then, was the final battle of the three first-year armies that would determine the awarding of Professor Quirrell's thrice-cursed Christmas wish.

  Dumbledore glanced over at her, studying her gravely. "You fear that the explosion will come then, and someone will be hurt."

  Minerva nodded.

  "And that Professor Quirrell will be blamed."

  Minerva nodded again, her face tight. She had long since become wise in the ways that Defense Professors were fired. "Albus," Minerva said, "we cannot lose Professor Quirrell now, we cannot! If he but stays through January our fifth-years will pass their OWLs, if he stays through March our seventh-years will pass their NEWTs, he is remedying years of neglect in months, a whole generation will grow up able to defend themselves in spite of the Dark Lord's curse - you must stop the battle, Albus! Ban the armies now!"

  "I am not sure the Defense Professor would take that kindly," said Dumbledore, glancing over toward the Head Table where Quirrell was drooling into his soup. "He did seem most attached to his armies, though when I agreed I thought there would be four in each year." The old wizard sighed. "A clever man, probably with the best of intentions; but perhaps not clever enough, I fear. And to ban the armies might also trigger the explosion."

  "But then Albus, what will you do?"

  The old wizard favored her with a benign smile. "Why, I shall plot, of course. It's the new fashion in Hogwarts."

  And they had come too close to the Head Table for Minerva to say anything more.

  The terrifying part was how fast the whole thing had spiraled out of control.

  The first battle in December had been... messy, or so Draco had heard.

  The second battle had been deranged.

  And the next one would be worse, unless the three of them together succeeded in their last desperate attempt to stop it.

  "Professor Quirrell, this is insanity," Draco said flatly. "This isn't Slytherin any more, it's just..." Draco was at a loss for words. He waved his hands helplessly. "You can't possibly do any real plots with all this stuff going on. Last battle, one of my soldiers faked his own suicide. We have Hufflepuffs trying to plot, and they think they can, but they can't. Things just happen at random now, it doesn't have anything to do with who's cleverest, or which army fights best, it's..." He couldn't even describe it.

  "I agree with Mr. Malfoy," said Granger in the tones of someone who hadn't ever expected to hear herself saying those words. "Allowing traitors isn't working, Professor Quirrell."

  Draco had tried forbidding anyone in his army to plot except him, and that had just driven the plots underground, no one wanted to be left out when the soldiers in other armies got to plot. After miserably losing their last battle, he'd finally given in and revoked his decree; but by then his soldiers had already started setting their own personal plans in motion, without any sort of central coordination.

  After being told all the plans, or what his soldiers claimed were their plans, Draco had tried to sketch a plot to win the final battle. It had required considerably more than three different things to go right, and Draco had used Incendio on the paper and Everto to vanish the ashes, because if Father had seen it he would have been disowned.

  Professor Quirrell's eyelids were half-closed, his chin resting on his hands as he leaned forward onto his desk. "And you, Mr. Potter?" said the Defense Professor. "Are you likewise in agreement?"

  "All we'd need to do is shoot Franz Ferdinand and we could start World War One," said Harry. "It's gone to complete chaos. I'm all for it."

  "Harry!" said Draco in utter shock.

  He didn't even realize until a second later that he'd said it at exactly the same time, and in exactly the same tone of indignation, as Granger.

  Granger shot him a startled glance, and Draco carefully kept his face neutral. Oops.

  "That's right!" said Harry. "I'm betraying you! Both of you! Again! Ha ha!"

  Professor Quirrell was smiling thinly, though his eyes were still half-closed. "And why is that, Mr. Potter?"

  "Because I think I can cope with the chaos better than Miss Granger or Mr. Malfoy," said the traitor. "Our war is a zero-sum game, and it doesn't matter whether it's easy or hard in an absolute sense, only who does better or worse."

  Harry Potter was learning far too fast.

  Professor Quirrell's eyes moved beneath their lids to regard Draco, and then Granger. "In truth, Mr. Malfoy, Miss Granger, I simply could not live with myself if I shut down the grand debacle before its climax. One of your soldiers has even become a quadruple agent."

  "Quadruple?" said Granger. "But there's only three sides in the war!"

  "Yes," said Professor Quirrell, "you'd think that, wouldn't
you. I am not sure that there has ever in history been a quadruple agent, or any army with such a high fraction of real and pretended traitors. We are exploring new realms, Miss Granger, and we cannot turn back now."

  Draco left the Defense Professor's office with his teeth gritting hard against each other, and Granger looking even more annoyed beside him.

  "I can't believe you did that, Harry!" said Granger.

  "Sorry," Harry said, not sounding sorry at all, his lips curved up in a merry smile of evil. "Remember, Hermione, it is just a game, and why should generals like us be the only ones who get to plot? And besides, what are the two of you going to do about it? Team up against me?"

  Draco traded glances with Granger, knowing that his own face was as tight as hers. Harry had been relying, more and more openly and gloatingly, on Draco's refusal to make common cause with a mudblood girl; and Draco was beginning to get sick of having that used against him. If this kept up much longer he was going to ally with Granger just to crush Harry Potter, and see how much the son of a mudblood liked that.

  The terrifying part was how fast the whole thing had spiraled out of control.

  Hermione stared at the parchment Zabini had given her, feeling utterly and completely helpless.

  There were names, and lines connecting the names to other names, and some of the lines were in different colors and...

  "Tell me," said General Granger, "is there anyone in my army who isn't a spy?"

  The two of them weren't in the office but in another, deserted classroom, and they were alone; because, Colonel Zabini had said, it was now nearly certain that at least one of the captains was a traitor. Probably Captain Goldstein, but Zabini didn't know for sure.

  Her question had put an ironic smile on the young Slytherin's face. Blaise Zabini always seemed a little disdainful of her, but he didn't seem to actively dislike her; nothing like the derision he held for Draco Malfoy, or the resentment he had developed for Harry Potter. She had worried at first about Zabini betraying her, but the boy seemed desperate to show that the other two generals were no better than him; and Hermione thought that while Zabini would probably be happy to sell her out to anyone else, he'd never let Malfoy or Harry win.

  "Most of your soldiers are still loyal to you, I'm pretty sure," said Zabini. "It's just that no one wants to be left out of the fun." The scornful look on the Slytherin's face made it clear what he thought of people who didn't take plotting seriously. "So they think they can be double agents and secretly work for our side while pretending to betray us."

  "And that would also go for anyone in the other armies who says they want to be our spy," Hermione said carefully.

  The young Slytherin shrugged. "I think I did a good job of telling which ones really want to sell out Malfoy, I'm not sure anyone really wants to sell out Potter to you. But Nott is a sure bet for betraying Potter to Malfoy and since I had Entwhistle approach him supposedly on behalf of Malfoy and Entwhistle really reports to us, that's almost as good -"

  Hermione closed her eyes for a moment. "We're going to lose, aren't we?"

  "Look," Zabini said patiently, "You're in the lead right now on Quirrell points. We just have to not lose this last battle completely and you'll have enough Quirrell points to win the Christmas wish."

  Professor Quirrell had announced that the final battle would operate on a formal scoring system, which he'd been asked to do to avoid recriminations afterward. Each time you shot someone, the general of your army got two Quirrell points. A gong would ring through the battle area (they didn't know yet where they would be fighting, though Hermione was hoping for the forest again, where Sunshine did well) and its pitch would tell which army had won the points. And if anyone was faking being hit, the gong would ring out anyway, and then a double gong would ring later, after no fixed time, to hail the retraction. And if you called the name of an army, cried "For Sunshine!" or "For Chaos!" or "For Dragon!", it switched your allegiance to that army...

  Even Hermione had been able to see the flaw in that set of rules. But Professor Quirrell had gone on to announce that if you'd been originally assigned to Sunshine, nobody could shoot you in the name of Sunshine - or rather, they could, but then Sunshine lost a single Quirrell point, symbolized by a triple gong. That prevented you from shooting your own soldiers for points, and discouraged suiciding before the enemy got you, but you could still shoot spies if you had to.

  Right now, Hermione had two hundred and forty-four Quirrell points, and Malfoy had two hundred and nineteen, and Harry had two hundred and twenty-one; and there were twenty-four soldiers in each army.

  "So we fight carefully," Hermione said, "and just try not to lose too badly."

  "No," said Zabini. The young Slytherin's face was now serious. "The problem is, Malfoy and Potter both know that their only way to win is to combine and crush us, then fight it out on their own. So here's what I think we should do -"

  Hermione left the classroom in something of a daze. Zabini's plan hadn't been the obvious one, it had been strange and complicated and layered and the sort of thing she would've expected Harry to come up with, not Zabini. It felt wrong just for her to be able to understand a plan like that. Young girls shouldn't be able to understand plans like that. The Hat would've Sorted her into Slytherin, if it'd seen that she could understand plans like that...

  The awesome thing was how fast he'd been able to escalate the chaos once he started doing it deliberately.

  Harry sat in his office; he'd been given the authority to order furniture from the house elves, so he'd ordered a throne, and curtains in a black and crimson pattern. Scarlet light like blood, mixed with shadow, poured over the floor.

  Something in Harry felt like he'd finally come home.

  Before him stood the four Lieutenants of Chaos, his most trusted minions, one of whom was a traitor.

  This. This was what life should be like.

  "We are gathered," said Harry.

  "Let Chaos reign," chorused his four Lieutenants.

  "My hovercraft is full of eels," said Harry.

  "I will not buy this record, it is scratched," chorused his four Lieutenants.

  "All mimsy were the borogroves."

  "And the mome raths outgrabe!"

  That concluded the formalities.

  "How goes the confusion?" Harry said in a dry whisper like Emperor Palpatine.

  "It goes well, General Chaos," said Neville in the tone he always used for military matters, a tone so deep that the boy often had to stop and cough. The Chaotic Lieutenant was neatly dressed in his black school robes, trimmed in the yellow of Hufflepuff House, and his hair was parted and combed in the usual look for an earnest young boy. Harry had liked the incongruity better than any of the cloaks they'd tried. "Our Legionnaires have begun five new plots since yesterday evening."

  Harry smiled evilly. "Do any of them have a chance of working?"

  "I don't think so," said Neville of Chaos. "Here's the report."

  "Excellent," said Harry, and laughed chillingly as he took the parchment from Neville's hand, trying his best to make it sound like he was choking on dust. That brought the total to sixty.

  Let Draco try to handle that. Let him try.

  And as for Blaise Zabini...

  Harry laughed again, and this time it didn't even take an effort to sound evil. He really needed to borrow someone's pet Kneazle for his staff meetings, so he'd have a cat to stroke while he did this.

  "Can the Legion stop making plots now?" said Finnigan of Chaos. "I mean, don't we have enough already -"

  "No," Harry said flatly. "We can never have enough plots."

  Professor Quirrell had put it perfectly. They were pushing the boundaries further, perhaps, than they had ever been pushed; and Harry wouldn't have been able to live with himself if he'd turned back now.

  There came a knock at the door.

  "That will be the Dragon General," Harry said, smiling with evil prescience. "He arrives precisely as I expected. Do show him in, and yourselv
es out."

  And the four Lieutenants of Chaos shuffled out, casting dark looks at Draco as the enemy general entered into Harry's secret lair.

  If he wasn't allowed to do this when he was older, Harry was just going to stay eleven forever.

  The sun was dripping through the red curtains, sending rays of blood dancing across the floor from behind Harry Potter's grownup-sized cushioned chair, which he had covered in gold and silver glitter and insisted on referring to as his throne.

  (Draco was beginning to feel a lot more confident that he'd done the right thing in deciding to overthrow Harry Potter before he could take over the world. Draco couldn't even imagine what it would be like to live under his rule.)

  "Good evening, Dragon General," said Harry Potter in a chill whisper. "You have arrived just as I expected."

  This was not surprising, considering that Draco and Harry had agreed on the meeting time in advance.

  And it also wasn't evening, but by now Draco knew better than to say anything.

  "General Potter," Draco said with as much dignity as he could manage, "you know that our two armies have to work together for either of us to win Professor Quirrell's wish, right?"

  "Yesss," hissed Harry, like the boy thought he was a Parselmouth. "We must cooperate to destroy Sunshine, and only then fight it out between us. But if one of us betrays the other earlier on, that one could gain an advantage in the later fight. And the Sunshine General, who knows all this, will try to trick each of us into thinking the other has betrayed them. And you and I, who know that, will be tempted to betray the other and pretend that it is Granger's trickery. And Granger knows that, as well."

  Draco nodded. That much was obvious. "And... both of us only want to win, and there's no one else who'll punish either of us if we defect..."

  "Precisely," said Harry Potter, his face now turning serious. "We are faced with a true Prisoner's Dilemma."

  The Prisoner's Dilemma, according to Harry's teachings, ran thus: Two prisoners had been locked in separate cells. There was evidence against each prisoner, but only minor evidence, enough for a prison sentence of two years apiece. Each prisoner could opt to defect, betray the other, testify against them in court; and this would take one year off their own prison sentence, but add two years to the other's. Or a prisoner could cooperate, staying silent. So if both prisoners defected, each testifying against the other, they would serve three years apiece; if both cooperated, or stayed silent, they would serve two years each; but if one defected and the other cooperated, the defector would serve a single year, and the cooperator would serve four.