Harry Potter and the Methods of Rationality

by Eliezer Yudkowsky

  Draco had tried to point out the staggering stupidity of this by suggesting that the key to surviving a duel was to cast Avada Kedavra on your own foot and miss.

  Harry Potter had nodded.

  Draco had shaken his head.

  Harry Potter had then presented the idea that scientists watched ideas fight to see which ones won, and you couldn't fight without an opponent, so Draco needed to figure out opponents for the blood purist hypothesis to fight so that blood purism could win, which Draco understood a little better even though Harry Potter had said it with a rather distasteful look. Like, it was clear that if blood purism was the way the world really was, then the sky just had to be blue, and if some other theory was true, the sky just had to be green; and nobody had seen the sky yet; and then you went outside and looked and the blood purists won; and after this had happened six times in a row, people would start noticing the trend.

  Harry Potter had then proceeded to claim that all the opponents Draco was inventing were too weak, so blood purism wouldn't get credit for defeating them because the battle wouldn't be impressive enough. Draco had understood that too. Wizards have gotten weaker because house elves are stealing our magic hadn't sounded impressive to him either.

  (Though Harry Potter had said that one at least was testable, in that they could try to check if house elves had gotten stronger over time, and even draw a picture representing the increasing strength of house elves and another picture representing the decreasing strength of wizards and if the two pictures matched that would point to the house elves, all said in such completely serious tones that Draco had felt an impulse to ask Dobby a few pointed questions under Veritaserum before snapping out of it.)

  And Harry Potter had finally said that Draco couldn't fix the battle, scientists weren't dumb, it would be obvious if you fixed the battle, it had to be a real fight, between two different theories that might both really be true, with a test that only the true hypothesis would win, something that actually would come out different ways depending on which hypothesis was actually correct, and there would be experienced scientists watching to make sure that was exactly what happened. Harry Potter had claimed that he himself just wanted to know how blood really worked and for that he need to see blood purism really win and Draco wasn't going to fool him with theories that were just there to be knocked down.

  Even having seen the point, Draco hadn't been able to invent any "plausible alternatives", as Harry Potter put it, to the idea that wizards were getting less powerful because they were mixing their blood with mud. It was too obviously true.

  It was then that Harry Potter had said, rather frustrated, that he couldn't imagine Draco was really this bad at considering different viewpoints, surely there'd been Death Eaters who'd posed as enemies of blood purism and had come up with much more plausible-sounding arguments against their own side than Draco was offering. If Draco had been trying to pose as a member of Dumbledore's faction, and come up with the house elf hypothesis, he wouldn't have fooled anyone for a second.

  Draco had been forced to admit this was a point.

  Hence the Potter Method.

  "Please, Dr. Malfoy," whined Harry Potter, "why won't you accept my paper?"

  Harry Potter had needed to repeat the phrase "just pretend to be pretending to be a scientist" three times before Draco had understood.

  In that moment Draco had realized that there was something deeply wrong with Harry Potter's brain, and anyone who tried Legilimency on it would probably never come back out again.

  Harry Potter had then gone into further and considerable detail: Draco was to pretend to be a Death Eater who was posing as the editor of a scientific journal, Dr. Malfoy, who wanted to reject his enemy Dr. Potter's paper "On the Heritability of Magical Ability", and if the Death Eater didn't act like a real scientist would, he would be revealed as a Death Eater and executed, while Dr. Malfoy was also being watched by his own rivals and needed to appear to reject Dr. Potter's paper for neutral scientific reasons or he would lose his position as journal editor.

  It was a wonder the Sorting Hat wasn't gibbering madly in St. Mungo's.

  It was also the most complicated thing anyone had ever asked Draco to pretend and there was no possible way he could have refused the challenge.

  Right now they were, as Harry Potter had put it, getting in the mood.

  "I'm afraid, Dr. Potter, that you wrote this in the wrong color of ink," Draco said. "Next!"

  Dr. Potter's face did an excellent job of crumpling in despair, and Draco couldn't help but feel a flash of Dr. Malfoy's glee, even though the Death Eater was only pretending to be Dr. Malfoy.

  This part was fun. He could have done this all day long.

  Dr. Potter got up from the chair, slumped over in dismay, and trudged off, and turned into Harry Potter, who gave Draco a thumbs-up, and then turned back into Dr. Potter again, now approaching with an eager smile.

  Dr. Potter sat down and presented Dr. Malfoy with a piece of parchment on which was written:

  On the Heritability of Magical Ability

  Dr. H. J. Potter-Evans-Verres, Institute for Sufficiently Advanced Science

  My observation:

  Today's wizards can't do things as impressive as

  what wizards used to do 800 years ago.

  My conclusion:

  Wizardkind has become weaker by mixing

  their blood with Muggleborns and Squibs.

  "Dr. Malfoy," said Dr. Potter with a hopeful look, "I was wondering if the Journal of Irreproducible Results could consider for publication my paper entitled 'On the Heritability of Magical Ability'."

  Draco looked at the parchment, smiling while he considered possible rejections. If he was a professor, he would have refused the essay as too short, so -

  "It's too long, Dr. Potter," said Dr. Malfoy.

  For a moment there was genuine incredulity on Dr. Potter's face.

  "Ah..." said Dr. Potter. "How about if I get rid of the separate lines for observations and conclusions, and just put in a therefore -"

  "Then it'll be too short. Next!"

  Dr. Potter trudged off.

  "All right," said Harry Potter, "you're getting too good at this. Two more times to practice, and then third time is for real, no interruptions between, I'll just come in straight at you and that time you'll reject the paper based on the actual content, remember, your scientific rivals are watching."

  Dr. Potter's next paper was perfect in every way, a marvel of its kind, but unfortunately had to be rejected because Dr. Malfoy's journal was having trouble with the letter E. Dr. Potter offered to rewrite it without those words, and Dr. Malfoy explained that it was really more of a vowel problem.

  The paper after that was rejected because it was Tuesday.

  It was, in fact, Saturday.

  Dr. Potter tried to point this out and was told "Next!"

  (Draco was starting to understand why Snape had used his hold over Dumbledore just to get a position that let him be awful to students.)

  And then -

  Dr. Potter was approaching with a superior smirk on his face.

  "This is my latest paper, On the Heritability of Magical Ability," Dr. Potter stated confidently, and thrust out the parchment. "I have decided to allow your journal to publish it, and have prepared it in perfect accordance with your guidelines so that you may publish it quickly."

  The Death Eater decided to track down and kill Dr. Potter after his mission was done. Dr. Malfoy kept a polite smile on his face, since his rivals were watching, and said...

  (The pause stretched, with Dr. Potter looking at him impatiently.)

  ..."Let me look at that, please."

  Dr. Malfoy took the parchment and perused it carefully.

  The Death Eater was starting to get nervous about the fact that he wasn't a real scientist, and Draco was trying to remember how to talk like Harry Potter.

  "You, ah, need to consider other possible explanations for your, um, observation, besides just this o
ne -"

  "Really?" interrupted Dr. Potter. "Like what, exactly? House elves are stealing our magic? My data admit of only one possible conclusion, Dr. Malfoy. There are no other plausible hypotheses."

  Draco was trying furiously to order his brain to think, what would he say if he was posing as a member of Dumbledore's faction, what did they claim was the explanation for wizardkind's decline, Draco had never bothered to actually ask that...

  "If you can't think of any other way to explain my data, you'll have to publish my paper, Dr. Malfoy."

  It was the sneer on Dr. Potter's face that did it.

  "Oh yeah?" snapped Dr. Malfoy. "How do you know that magic itself isn't fading away?"

  Time stopped.

  Draco and Harry Potter exchanged looks of appalled horror.

  Then Harry Potter spat something that was probably an extremely bad word if you'd been raised by Muggles. "I didn't think of that!" said Harry Potter. "And I should have. The magic goes away. Damn, damn, damn!"

  The alarm in Harry Potter's voice was contagious. Without even thinking about it, Draco's hand went into his robes and clutched at his wand. He'd thought the House of Malfoy was safe, so long as you only married into families that could trace their bloodlines back four generations you were supposed to be safe, it had never occurred to him before that there might be nothing anyone could do to stop the end of magic. "Harry, what do we do?" Draco's voice was rising in panic. "What do we do?"

  "Let me think!"

  After a few moments, Harry grabbed from a nearby desk the same quill and roll of parchment he'd used to write his pretend paper, and started scribbling something.

  "We'll figure it out," Harry said, his voice tight, "if magic is fading out of the world we'll figure out how fast it's fading and how much time we have left to do something, and then we'll figure out why it's fading, and then we'll do something about it. Draco, have wizarding powers been declining at a steady rate, or have there been sudden drops?"

  "I... I don't know..."

  "You told me that no one had matched the four founders of Hogwarts. So it's been going on for at least eight centuries, then? You can't remember hearing anything about the problems suddenly appearing five centuries ago or anything like that?"

  Draco was trying frantically to think. "I always heard that nobody was as good as Merlin and then after that nobody was as good as the Founders of Hogwarts."

  "All right," Harry said. He was still scribbling. "Because three centuries ago is when Muggles started to not believe in magic, which I thought might have something to do with it. And about a century and a half ago was when Muggles began using a kind of technology that stops working around magic and I was wondering if it might also go the other way around."

  Draco exploded out of his chair, so angry he could hardly even speak. "It's the Muggles -"

  "Damn it!" roared Harry. "Weren't you even listening to yourself? It's been going on for eight centuries at least and the Muggles weren't doing anything interesting then! We have to figure out the real truth! The Muggles might have something to do with this but if they don't and you go blaming everything on them and that stops us from figuring out what's really going on then one day you're going to wake up in the morning and find out that your wand is just a stick of wood!"

  Draco's breath stopped in his throat. His father often said our wands will break in our hands in his speeches but Draco had never really thought before about what that meant, it wasn't going to happen to him after all. And now suddenly it seemed very real. Just a stick of wood. Draco could imagine just what it would be like to take out his wand and try to cast a spell and find that nothing was happening...

  That could happen to everyone.

  There would be no more wizards, no more magic, ever. Just Muggles who had a few legends about what their ancestors had been able to do. Some of the Muggles would be called Malfoy, and that would be all that was left of the name.

  For the first time in his life, Draco realized why there were Death Eaters.

  He'd always taken for granted that becoming a Death Eater was something you did when you grew up. Now Draco understood, he knew why Father and Father's friends had sworn to give their lives to prevent the nightmare from coming to pass, there were things you couldn't just stand by and watch happen. But what if it was going to happen anyway, what if all the sacrifices, all the friends they'd lost to Dumbledore, the family they'd lost, what if it had all been for nothing...

  "Magic can't be fading away," Draco said. His voice was breaking. "It wouldn't be fair."

  Harry stopped scribbling and looked up. His face had an angry expression. "Your father never told you that life isn't fair?"

  Father had said that every single time Draco used the word. "But, but, it's too awful to believe that -"

  "Draco, let me introduce you to something I call the Litany of Tarski. It changes every time you use it. On this occasion it runs like so: If magic is fading out of the world, I want to believe that magic is fading out of the world. If magic is not fading out of the world, I want not to believe that magic is fading out of the world. Let me not become attached to beliefs I may not want. If we're living in a world where magic is fading, that's what we have to believe, we have to know what's coming, so we can stop it, or in the very worst case, be prepared to do what we can in the time we have left. Not believing it won't stop it from happening. So the only question we have to ask is whether magic is actually fading, and if that's the world we live in then that's what we want to believe. Litany of Gendlin: What's true is already so, owning up to it doesn't make it worse. Got that, Draco? I'm going to make you memorize it later. It's something you repeat to yourself any time you start wondering if it's a good idea to believe something that isn't actually true. In fact I want you to say it right now. What's true is already so, owning up to it doesn't make it worse. Say it."

  "What's true is already so," repeated Draco, his voice trembling, "owning up to it doesn't make it worse."

  "If magic is fading, I want to believe that magic is fading. If magic is not fading, I want not to believe that magic is fading. Say it."

  Draco repeated back the words, the sickness churning in his stomach.

  "Good," Harry said, "remember, it might not be happening, and then you won't have to believe it, either. First we just want to know what's actually going on, which world we actually live in." Harry turned back to his work, scribbled some more, and then turned the parchment so Draco could see it. Draco leaned over the desk and Harry brought the green light closer.

  Observation:

  Wizardry isn't as powerful now as it was when Hogwarts was founded.

  Hypotheses:

  1. Magic itself is fading.

  2. Wizards are interbreeding with Muggles and Squibs.

  3. Knowledge to cast powerful spells is being lost.

  4. Wizards are eating the wrong foods as children, or something else besides blood is making them grow up weaker.

  5. Muggle technology is interfering with magic. (Since 800 years ago?)

  6. Stronger wizards are having fewer children. (Draco = only child? Check if 3 powerful wizards, Quirrell / Dumbledore / Dark Lord, had any children.)

  Tests:

  "All right," Harry said. His breathing sounded a little calmer. "Now when you're dealing with a confusing problem and you have no idea what's going on, the smart thing to do is figure out some really simple tests, things you can look at right away. We need fast tests that distinguish between these hypotheses. Observations that would come out a different way for at least one of them compared to all the other ones."

  Draco stared at the list in shock. He was suddenly realizing that he knew an awful lot of purebloods who were only children. Himself, Vincent, Gregory, practically everyone. The two most powerful wizards everyone talked about were Dumbledore and the Dark Lord and neither had any children just like Harry had suspected...

  "It's going to be really hard to distinguish between 2 and 6," Harry said, "it's in the blood either w
ay, you'd have to try and track the decline of wizardry and compare that to how many kids different wizards were having and measure the abilities of Muggleborns compared to purebloods..." Harry's fingers were tapping nervously on the desk. "Let's just lump 6 in with 2 and call them the blood hypothesis for now. 4 is unlikely because then everyone would notice a sudden drop when the wizards switched to new foods, it's hard to see what would've changed steadily over 800 years. 5 is unlikely for the same reason, no sudden drop, Muggles weren't doing anything 800 years back. 4 looks like 2 and 5 looks like 1 anyway. So mainly we should be trying to distinguish between 1, 2, and 3." Harry turned the parchment to himself, drew an ellipse around those three numbers, turned it back. "Magic is fading, blood is weakening, knowledge is disappearing. What test comes out differently depending on which of those is true? What could we see that would mean any one of these was false?"

  "I don't know!" blurted Draco. "Why are you asking me? You're the scientist!"

  "Draco," Harry said, a note of pleading desperation in his voice, "I only know what Muggle scientists know! You grew up in the wizarding world, I didn't! You know more magic than I do and you know more about magic than I do and you thought of this whole idea in the first place, so start thinking like a scientist and solve this!"

  Draco swallowed hard and stared at the paper.

  Magic is fading... wizards are interbreeding with Muggles... knowledge is being lost...

  "What does the world look like if magic is fading?" said Harry Potter. "You know more about magic, you should be the one guessing not me! Imagine you're telling a story about it, what happens in the story?"

  Draco imagined it. "Charms that used to work stop working." Wizards wake up and find that their wands are sticks of wood...

  "What does the world look like if the wizarding blood gets weaker?"

  "People can't do things their ancestors could do."