Harry Potter and the Methods of Rationality

by Eliezer Yudkowsky

  Without word, without sound, a sphere of fire surrounded the bird's form, crackling and blazing with white and crimson veins as though it meant to consume that which lay within; and when the fire dispersed into grey smoke, no phoenix remained.

  There was silence on the top of the Ravenclaw tower. The boy gradually lowered his hands from his ears, pausing only to wipe at his wet cheeks.

  Slowly, the boy turned -

  Then cried out and leapt back and almost fell off the Ravenclaw tower; though the misstep would hardly have mattered, with that other wizard standing there.

  "And so it was done," Albus Dumbledore said, almost in a whisper. "So it was done." Fawkes was on his shoulder, staring at where the other phoenix had been with an indecipherable avian gaze.

  "What are you doing here?"

  "Ah?" said the ancient man standing on the roof-platform's opposite corner. "I felt the presence of a creature Hogwarts did not know, and came to see, of course." Slowly the old wizard's shaking hand came up to remove the half-moon glasses, his other hand wiped at his eyes and forehead with his robe's sleeve. "I dared - I dared not speak - I knew, I knew this choice above all choices must be your own -"

  A strange apprehension was beginning to fill Harry, welling up in him like a sick feeling in his stomach.

  "That everything depended on this," Albus Dumbledore said, still in that almost-whisper, "that much I knew. But which choice led into darkness, that I could not guess. At least the choice was your own."

  "I don't -" Harry said, and then his voice stopped.

  A terrible hypothesis, rising in credibility...

  "The phoenix comes," said the old wizard. "To those who would fight, to those would act even at cost of their lives, the phoenix comes. Phoenixes are not wise, Harry, they know no means to judge us, save witnessing the choice. I thought it was to my death I went, when the phoenix took me to fight Grindelwald. I did not know that Fawkes would sustain me, and heal me, and stay by my side -" The old wizard's voice quavered, for a moment. "It is not spoken of - you should realize, Harry, why it is never spoken of - if the one knew, the phoenix could not judge. But to you, Harry, I may say it now, for the phoenix comes only once."

  The old wizard walked across the top of the Ravenclaw tower to where a boy stood rooted in dawning horror, in dawning and utter horror.

  In my duel with Grindelwald I could not win, only fight him for long hours until he collapsed in exhaustion; and I would have died of it afterward, if not for Fawkes -

  Harry didn't even know he was speaking, until the whisper had escaped him -

  "Then I could have -"

  "Could you have?" said the ancient wizard, his voice sounding far older than his normal tones. "Three times, now, a phoenix has come for my student. One did send hers away, and the grief of it broke her, I think. And the last was cousin to your young friend Lavender Brown, and he -" The old wizard's voice cracked. "He did not return, did poor John, and he saved none of those he meant to save. It is said, among the few scholars of phoenix-lore, that not one in four returns from their ordeal. And even if you did survive - for the life you must lead, Harry James Potter-Evans-Verres - the choices you must make and the path you must walk - to always hear the phoenix's cries - who is to say it would not have driven you mad?" The old wizard raised his sleeve again, drawing it once more across his face. "I had more joy of Fawkes's companionship, in the days before I fought Voldemort."

  The boy did not seem to be listening, all his eyes were on the red-gold bird on the ancient wizard's shoulder. "Fawkes?" the boy said in shaking voice. "Why won't you look at me, Fawkes?"

  Fawkes craned his head to peer at the boy curiously, then turned back and resumed gazing at his master.

  "See?" said the old wizard. "He does not reject you. Fawkes may not be interested in you in quite that way, now; and he knows -" the wizard smiled wryly, "- that you are not exactly loyal to his master. But one to whom the phoenix comes at all - cannot be one whom a phoenix would dislike." The wizard's voice fell to a whisper again. "There never was a bird seen on Godric Gryffindor's shoulder. Though it is not written even in his secrets, I think he must have sent his phoenix away, before he chose the red and gold for his colors. Perhaps the guilt of it urged him to greater lengths than he ever would have dared otherwise. Or it might have taught him humility, and respect for human frailty, and failure..." The wizard bowed his head. "I truly do not know if your choice was wise. I truly do not know if it was the right thing, or the wrong thing. If I knew, Harry, I would have spoken. But I -" Dumbledore's voice broke, then. "I am nothing but a foolish young boy who has become a foolish old man, and I have no wisdom."

  Harry couldn't breathe, the nausea seeming to fill and overflow his whole body, stomach locked solid. He was suddenly and terribly certain that he had failed, in some final sense failed, failed this very night -

  The boy whirled and ran out to the curb of the Ravenclaw rooftop. "Come back!" His voice cracked, rising to a shriek. "Come back!"

  Final Aftermath:

  She came awake with a gasp of horror, she woke with an unvoiced scream on her lips and no words came forth, she could not understand what she had seen, she could not understand what she had seen -

  "What time is it?" she whispered.

  Her golden jeweled alarm clock whispered back, "Around eleven at night. Go back to sleep."

  Her sheets were soaked in sweat, her nightclothes soaked in sweat, she took her wand from beside the pillow and cleaned herself up before she tried to go back to sleep and eventually succeeded.

  Sybill Trelawney went back to sleep.

  In the Forbidden Forest, a centaur woken by a nameless apprehension ceased scanning the night sky, having found only questions there and no answers; and with a folding of his many legs, Firenze went back to sleep.

  In the distant lands of magical Asia, an ancient witch named Fan Tong, sleeping the tired days away, told her anxious great-great-grandson that she was fine, it had only been a nightmare, and went back to sleep.

  In a land where Muggleborns received no letters of any kind, a girl-child too young to have a name of her own was rocked in the arms of her annoyed but loving mother until she stopped crying and went back to sleep.

  None of them slept well.

  Chapter 86: Multiple Hypothesis Testing

  (International news headlines of April 7th, 1992:)

  Toronto Magical Tribune:

  ENTIRE BRITISH WIZENGAMOT

  REPORTS SEEING 'BOY-WHO-LIVED'

  FRIGHTEN A DEMENTOR

  EXPERT ON MAGICAL CREATURES:

  "NOW YOU'RE JUST LYING"

  FRANCE, GERMANY ACCUSE BRITAIN

  OF MAKING THE WHOLE THING UP

  New Zealand Spellcrafter's Diurnal Notice:

  WHAT DROVE BRITISH LEGISLATURE INSANE?

  COULD OUR GOVERNMENT BE NEXT?

  EXPERTS LIST TOP 28 REASONS

  TO BELIEVE IT'S ALREADY HAPPENED

  American Mage:

  WEREWOLF CLAN TO BECOME

  FIRST INHABITANTS OF WYOMING

  The Quibbler:

  MALFOY FLEES HOGWARTS

  AS VEELA POWERS AWAKEN

  Daily Prophet:

  LEGAL TRICKS FREE

  "MAD MUGGLEBORN"

  AS POTTER THREATENS MINISTRY

  WITH ATTACK ON AZKABAN

  Hypothesis: Voldemort

  (April 8th, 1992, 7:22pm)

  The four of them gathered once more around the ancient desk of the Headmaster of Hogwarts, with its drawers within drawers within drawers, wherein all the past paperwork of the Hogwarts School was stored; legend had it that Headmistress Shehla had once gotten lost in that desk, and was, in fact, still there, and wouldn't be let out again until she got her files organized. Minerva didn't particularly look forward to inheriting those drawers, when she inherited that desk someday - if any of them survived.

  Albus Dumbledore was seated behind his desk, looking grave and composed.

  Severus Snape was standing next t
o the dead Floo and its ashes, hovering ominously like the vampire that students sometimes accused him of pretending to be.

  Mad-Eye Moody had been meant to join them, but was yet to arrive.

  And Harry...

  A boy's small, thin frame, perched on the arm of his chair, as though the energies running through him were too great to allow ordinary seating. Set face, sweaty hair, intent green eyes, and within it all, the jagged lightning-bolt of his never-healing scar. He seemed grimmer, now; even compared to a single week earlier.

  For a moment Minerva flashed back to her trip to Diagon Alley with Harry, what seemed like ages and ages ago. There'd been this somber boy inside that Harry, somehow, even then. This wasn't entirely her own fault, or Albus's fault. And yet there was something almost unbearably sad about the contrast between the young boy she'd first met, and what magical Britain had made of him. Harry had never had much of an ordinary childhood, she'd gathered; Harry's adoptive parents had said to her that he'd spoken little and played less with Muggle children. It was painful to think that Harry might have had only a few months of playing beside the other children in Hogwarts, before the war's demands had stripped it all away. Maybe there was another face that Harry showed to the children his own age, when he wasn't staring down the Wizengamot. But she couldn't stop herself from imagining Harry Potter's childhood as a heap of firewood, and herself and Albus feeding the wooden branches, piece by piece, into the flames.

  "Prophecies are strange things," said Albus Dumbledore. The old wizard's eyes were half-lidded, as though in weariness. "Vague, unclear, meaning escaping like water held between loose fingers. Prophecy is ever a burden, for there are no answers there, only questions."

  Harry Potter was sitting tensely. "Headmaster Dumbledore," said the boy with soft precision, "my friends are being targeted. Hermione Granger almost went to Azkaban. The war has begun, as you put it. Professor Trelawney's prophecy is key information for weighing up the balance of my hypotheses about what's going on. Not to mention how silly it is - and dangerous - that the Dark Lord knows the prophecy and I don't."

  Albus looked a grim question at her, and she shook her head in reply; in whatever unimaginable way Harry had discovered that Trelawney had made the prophecy and that the Dark Lord knew of it, he hadn't learned that much from her.

  "Voldemort, seeking to avert that very prophecy, went to his defeat at your hands," the old wizard said then. "His knowledge brought him only harm. Ponder that carefully, Harry Potter."

  "Yes, Headmaster, I do understand that. My home culture also has a literary tradition of self-fulfilling and misinterpreted prophecies. I'll interpret with caution, rest assured. But I've already guessed quite a bit. Is it safer for me to work from partial guesses?"

  Time passed.

  "Minerva," said Albus. "If you would."

  "The one..." she began. The words came falteringly to her throat; she was no actress. She couldn't imitate the deep, chilling tone of the original prophecy; and yet somehow that tone seemed to carry all the meaning. "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 shall mark him as his equal," came Severus's voice, making her jump within her chair. The Potions Master loomed tall by the fireplace. "But he shall 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."

  That last line Severus spoke with so much foreboding that it chilled her bones; it was almost like listening to Sybill Trelawney.

  Harry was listening with a frown. "Can you repeat that?" said Harry.

  "The one with the power to vanquish the Dark Lord approaches, born to those who have thrice defied him, born as the seventh month -"

  "Actually, hold on, can you write that down? I need to analyze this carefully -"

  This was done, with both Albus and Severus watching the parchment hawklike, as though to make sure that no unseen hand reached in and snatched the precious information away.

  "Let's see..." Harry said. "I'm male and born on July 31st, check. I did in fact vanquish the Dark Lord, check. Ambiguous pronoun in line two... but I wasn't born yet so it's hard to see how my parents could have thrice defied me. This scar is an obvious candidate for the mark..." Harry touched his forehead. "Then there's the power the Dark Lord knows not, which probably refers to my scientific background -"

  "No," said Severus.

  Harry looked at the Potions Master in surprise.

  Severus's eyes were closed, his face tightened in concentration. "The Dark Lord could obtain that power by studying the same books as you, Potter. But the prophecy did not say, power the Dark Lord has not. Nor even, power the Dark Lord cannot have. She spoke of power the Dark Lord knows not... it will be something stranger to him than Muggle artifacts. Something perhaps that he cannot comprehend at all, even having seen it..."

  "Science is not a bag of technological tricks," Harry said. "It's not just the Muggle version of a wand. It's not even knowledge like memorizing the periodic table. It's a different way of thinking."

  "Perhaps..." the Potions Master murmured, but his voice was skeptical.

  "It is hazardous," Albus said, "to read too far into a prophecy, even if you have heard it yourself. They are things of exceeding frustration."

  "So I see," Harry said. His hand rose up, rubbed the scar on his forehead. "But... okay, if this is really all we know... look, I'll just put it bluntly. How do you know that the Dark Lord actually survived?"

  "What?" she cried. Albus just sighed and leaned back in the vast Headmaster's chair.

  "Well," Harry said, "imagine how this prophecy sounded back when it was made. You-Know-Who learns the prophecy, and it sounds like I'm destined to grow up and overthrow him. That the two of us are meant to have a final battle where either of us must destroy all but a remnant of the other. So You-Know-Who attacks Godric's Hollow and immediately gets vanquished, leaving behind some remnant which may or may not be his disembodied soul. Maybe the Death Eaters are his remnant, or the Dark Mark. This prophecy could already be fulfilled, is what I'm saying. Don't get me wrong - I do realize that my interpretation sounds stretched. Trelawney's phrasing doesn't seem natural for describing only the events that historically happened on October 31st, 1981. Attacking a baby and having the spell bounce off, isn't something you'd normally call 'the power to vanquish'. But if you think of the prophecy as being about several possible futures, only one of which was actually realized on Halloween, then the prophecy could already be complete."

  "But -" Minerva blurted. "But the raid on Azkaban -"

  "If the Dark Lord survived, then sure, he's the most likely suspect for the Azkaban breakout," Harry said reasonably. "You could even say that the Azkaban breakout is Bayesian evidence for the Dark Lord surviving, because an Azkaban breakout is more likely to happen in worlds where he's alive than worlds where he's dead. But it's not strong Bayesian evidence. It's not something that can't possibly happen unless the Dark Lord is alive. Professor Quirrell, who didn't start from the assumption that You-Know-Who was still around, had no trouble thinking of his own explanation. To him, it was obvious that some powerful wizard might want Bellatrix Black because she knew a secret of the Dark Lord's, like some of his magical knowledge that he'd told to only her. The priors against anyone surviving their body's death are very low, even if it's magically possible. Most times it doesn't happen. So if it's just the Azkaban breakout... I'd have to say formally that it isn't enough Bayesian evidence. The improbability of the evidence assuming that the hypothesis is false, is not commensurate with the prior improbability of the hypothesis."

  "No," Severus said flatly. "The prophecy is not yet fulfilled. I would know if it were."

  "Are you sure of that?"

  "Yes, Potter. If the prophecy had already come true, I would understand it! I heard Trelawney's words, I remember Trelawney's voice, and if I knew the events that ma
tched the prophecy, I would recognize them. What has already happened... does not fit." The Potions Master spoke with certainty.

  "I'm not really sure what to do with that statement," Harry said. His hand rose up, absently rubbed at his forehead. "Maybe it's just what you think happened that doesn't fit, and the true history is different..."

  "Voldemort is alive," Albus said. "There are other indications."

  "Such as?" Harry's reply was instant.

  Albus paused. "There are terrible rituals by which wizards have returned from death," Albus said slowly. "That much, anyone can discern within history and legend. And yet those books are missing, I could not find them; it was Voldemort who removed them, I am sure -"

  "So you can't find any books on immortality, and that proves that You-Know-Who has them?"

  "Indeed," said Albus. "There is a certain book - I will not name it aloud - missing from the Restricted Section of the Hogwarts library. An ancient scroll which should have been at Borgin and Burkes, with only an empty place on a shelf to show where it was -" The old wizard stopped. "But I suppose," the old wizard said, as though to himself, "you will say that even if Voldemort tried to make himself immortal, it does not prove that he succeeded..."

  Harry sighed. "Proof, Headmaster? There are only ever probabilities. If there are known, particular books on immortality rituals which are missing, that increases the probability that someone attempted one. Which, in turn, raises the prior probability of the Dark Lord surviving his death. This I concede, and thank you for contributing the fact. The question is whether the prior probability goes up enough."

  "Surely," Albus said quietly, "if you concede even a chance that Voldemort survived, that is worth guarding against?"

  Harry inclined his head. "As you say, Headmaster. Though once a probability drops low enough, it's also an error to go on obsessing about it... Given that books on immortality are missing, and that this prophecy would sound somewhat more natural if it refers to the Dark Lord and I having a future battle, I agree that the Dark Lord being alive is a probability, not just possibility. But other probabilities must also be taken into account - and in the probable worlds where You-Know-Who is not alive, someone else framed Hermione."