Eliezer Yudkowsky - Harry Potter and the Methods of Rationality

Harry turned over the two-foot parchment.

On the other side, written in tiny letters, was the longest list of brewing instructions Harry had ever seen. “What on Earth—”

“A potion of effulgence, to quench the purple fire,” Professor Quirrell said. “It is made by adding the same ingredients, over and over again, in slightly different ways. Imagine some eager young group of first-years, passing all the other chambers, thinking they are just about to reach the magic mirror, and then encountering this task. This room is the handiwork of the Potions Master indeed.”

Harry glanced pointedly at the blackfire shape on Professor Quirrell’s shoulder. “Fire can’t beat fire?”

“It can,” said Professor Quirrell. “I am not sure it should. Suppose this room is trapped?”

Harry did not want to be stuck brewing this potion for laughs, or for whatever other reason Professor Quirrell was taking them through these chambers so slowly. The potions recipe had thirty-five separate occasions for adding bellflowers, fourteen times to add ‘a lock of bright hair’… “Maybe the potion gives off a lethal gas that is fatal to adult wizards but not children. Or any of a hundred other deadly tricks, if we’re suddenly being serious. Are we being serious?”

“This room is the handiwork of Severus Snape,” Professor Quirrell said, once more looking thoughtful. “Snape is not a bystander in this game, not quite. He lacks Dumbledore’s intelligence, but possesses the killing intent that Dumbledore never had.”

“Well, whatever’s going on here, it doesn’t actually keep out children,” Harry observed. “Lots of first-years made it through. And if you can somehow keep out everyone except children, then that, from Dumbledore’s perspective, forces Lord Voldemort to possess a child to enter. I don’t see the point, given their goals.”

“Indeed,” Professor Quirrell said, rubbing the bridge of his nose. “But see, boy, this room lacks the triggers and tripsigns that are upon the others. There are no subtle wards to be defeated. It is as if I am invited to bypass the Potion and simply enter—but Snape knows that Lord Voldemort will perceive this. If in fact there was a trap laid for anyone who did not brew the potion, then it would be wiser to lay wards, and give no sign that this room was different from the others.”

Harry listened, frowning in concentration. “So… the only point of leaving off the detection webs is to make you not bulldoze this room.”

“I expect Snape expects me to deduce that as well,” the Defense Professor said. “And past that point I cannot predict at what level he thinks I will play. I am patient, and I have given myself plenty of time for this endeavor. But Snape does not know me, he only knows Lord Voldemort. He has sometimes seen Lord Voldemort shriek in frustration, and act on impulses that appear counterproductive. Consider this matter from Snape’s perspective: it is the Potions Master of Hogwarts telling Lord Voldemort to be patient and follow instructions if he wants to enter, as though Lord Voldemort were a mere schoolboy. I would find it easy to comply, smiling the while, and take my vengeance later. But Snape does not know that Lord Voldemort finds it easy to think this way.” Professor Quirrell looked at Harry. “Boy, you saw me floating in the air by the Devil’s Snare, did you not?”

Harry nodded. Then he noticed his confusion. “My Charms textbook says that it’s impossible for wizards to levitate themselves.”

“Yes,” said Professor Quirrell, “that is what it says in your Charms textbook. No wizard may levitate themselves, or any object supporting their own weight; it is like trying to lift yourself up by your own bootstraps. Yet Lord Voldemort alone can fly—how? Answer as quickly as you can.”

If the question was answerable by a first-year student— “You had someone else cast broomstick enchantments on your underwear, then you Obliviated them.”

“Not quite,” said Professor Quirrell. “The broomstick enchantments require a long narrow shape, which must be solid. Cloth will not do.”

Harry’s eyebrows furrowed. “How long does the shape have to be? Can you attach some short broomstick rods to a fabric harness, and fly using those?”

“Indeed, at first I strapped enchanted rods to my arms and legs, but that was only to teach myself a new mode of flight.” Professor Quirrell drew back the sleeve of his robes, revealing the bare arm. “As you can see,

I have nothing up my sleeve right now.”

Harry absorbed this further constraint. “You had someone cast broomstick enchantments on your bones? ”

Professor Quirrell sighed. “And that was one of Voldemort’s most feared feats, or so I am told. After all these years, and some amount of reluctant Legilimency, I still do not truly comprehend what is wrong with ordinary people… But you are not one of them. It is time for you to begin contributing to this expedition. You have known Severus Snape more re-

cently than I. Tell me your own analysis of this room.” Harry hesitated, trying to look thoughtful.

“I will mention,” said Professor Quirrell, as the blackened-firephoenix on his shoulder seemed to extend its head and glare at Harry, “that if you knowingly allow me to fail, I will call it betrayal. I remind you that the Stone is key to Miss Granger’s resurrection, and that I hold hostage the lives of hundreds of students.”

“I remember,” Harry said, and on the heels of this Harry’s wonderful inventive brain came up with a thought.

Harry wasn’t sure if he should say it.

The silence stretched.

“Have you thought of anything yet?” said Professor Quirrell. “Answer in Parseltongue.”

No, this was not going to be easy, not against a smart opponent who could force you to tell the literal truth at any time. “Severus, at least the modern-day Severus, respects your intelligence a great deal,” Harry said instead. “I think… I think he might expect Voldemort to believe that Severus wouldn’t believe that Voldemort could pass his test of patience, but Severus would expect Voldemort to pass it.”

Professor Quirrell nodded. “That is a plausible theory. Do you believe it yourself? Answer in Parseltongue.”

“ Yess, ” Harry hissed. It might not be safe to withhold information, not even thoughts and ideas… “Therefore, the point of this room is to delay Lord Voldemort for an hour. And if I wanted to kill you, believing what

Dumbledore believes, the obvious thing to try would be a Dementor’s Kiss.

I mean, they think you’re a disembodied soul—are you, by the way?”

Professor Quirrell was still. “Dumbledore would not think of that method,” the Defense Professor said after a time. “But Severus might.” Professor Quirrell began to tap a finger against his cheek, his gaze distant. “You have power over Dementors, boy, can you tell me if there are any nearby?”

Harry closed his eyes. If there were voids in the world, he could not feel them. “None that I can sense.”

“Answer in Parseltongue.”

“ Do not ssensse life-eaterss. ”

“But you were being honest with me when you suggested the possibility? You intended no clever trickery?”

“ Wass honesst. Not trick. ”

“Perhaps there is some means by which Dementors might be concealed, being told to leap out and eat a possessing soul if they see one…” Professor Quirrell was still tapping his cheek. “It is not impossible that I would qualify. Or it can be told to eat anyone who passes through this room too quickly, or anyone who is not a child. Bearing in mind that I hold Hermione and hundreds of other students hostage over you, would you use your power over Dementors to defend me, if a Dementor unmasked itself? Answer in Parseltongue.”