Harry Potter and the methods of rationality

by Eliezer Yudkowsky

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Spoiler warning: no plot held back in this review.

science is at least as beautiful as magic permalink

In chapter 7 Harry introduces Draco to the beauty of scientific advancement, and it actually moved me to tears. You should read the whole thing, but here are some of the best quotes:

“Anyway,” Harry said, “I’m saying that you don’t seem to have been paying much attention to what goes on in the Muggle world.” Probably because the whole wizarding world seemed to regard the rest of Earth as a slum, deserving around as much news coverage as the Financial Times awarded to the routine agonies of Burundi. “All right. Quick check. Have wizards ever been to the Moon? You know, that thing?” Harry pointed up to that huge and distant globe.

“What? " Draco said. It was pretty clear the thought had never occured to the boy. “Go to the - it’s just a -” His finger pointed at the little pale thingy in the sky. “You can’t Apparate to somewhere you’ve never been and how would anyone get to the Moon in the first place?”

“Hold on,” Harry said to Draco, “I’d like to show you a book I brought with me, I think I remember what box it’s in.” And Harry stood up and kneeled down and yanked out the stairs to the cavern level of his trunk, then tore down the stairs and heaved a box off another box, coming perilously close to treating his books with disrespect, and snatched off the box cover and quickly but carefully pried out a stack of books -

… And Harry raced back up the stairs and shoved the staircase back into the trunk with his heel, and, panting, turned the pages of the book until he found the picture he wanted to show to Draco.

The one with the white, dry, cratered land, and the suited people, and the blue-white globe hanging over it all.

That picture.

The picture, if only one picture in all the world were to survive.

“That,” Harry said, his voice trembling because he couldn’t quite keep the pride out, “is what the Earth looks like from the Moon.”

Draco slowly leaned over. There was a strange expression on his young face. “If that’s a real picture, why isn’t it moving?”

Moving? Oh. “Muggles can do moving pictures but they need a bigger box to show it, they can’t fit them onto single book pages yet.”

Draco’s finger moved to one of the suits. “What are those?” His voice starting to waver.

“Those are human beings. They are wearing suits that cover their whole bodies to give them air, because there is no air on the Moon.”

“That’s impossible,” Draco whispered. There was terror in his eyes, and utter confusion. “No Muggle could ever do that. How…”

Harry took back the book, flipped the pages until he found what he saw. “This is a rocket going up. The fire pushes it higher and higher, until it gets to the Moon.” Flipped pages again. “This is a rocket on the ground. That tiny speck next to it is a person.” Draco gasped. “Going to the Moon cost the equivalent of… probably around a thousand million Galleons.” Draco choked. “And it took the efforts of… probably more people than live in all of magical Britain.” And when they arrived, they left a plaque that said, ‘We came in peace, for all mankind.’ Though you’re not yet ready to hear those words, Draco Malfoy…

“You’re telling the truth,” Draco said slowly. “You wouldn’t fake a whole book just for this - and I can hear it in your voice. But… but…”

“How, without wands or magic? It’s a long story, Draco. Science doesn’t work by waving wands and chanting spells, it works by knowing how the universe works on such a deep level that you know exactly what to do in order to make the universe do what you want. If magic is like casting Imperio on someone to make them do what you want, then science is like knowing them so well that you can convince them it was their own idea all along. It’s a lot more difficult than waving a wand, but it works when wands fail, just like if the Imperius failed you could still try persuading a person. And Science builds from generation to generation. You have to really know what you’re doing to do science - and when you really understand something, you can explain it to someone else. The greatest scientists of one century ago, the brightest names that are still spoken with reverence, their powers are as nothing to the greatest scientists of today. There is no equivalent in science of your lost arts that raised Hogwarts. In science our powers wax by the year. And we are beginning to understand and unravel the secrets of life and inheritance. We’ll be able to look at the very blood of which you spoke, and see what makes you a wizard, and in one or two more generations, we’ll be able to persuade that blood to make all your children powerful wizards too. So you see, your problem isn’t nearly as bad as it looks, because in a few more decades, science will be able to solve it for you.”

“But…” Draco said. His voice was trembling. “If Muggles have that kind of power… then… what are we? "

“No, Draco, that’s not it, don’t you see? Science taps the power of human understanding to look at the world and figure out how it works. It can’t fail without humanity itself failing. Your magic could turn off, and you would hate that, but you would still be you. You would still be alive to regret it. But because science rests upon my human intelligence, it is the power that cannot be removed from me without removing me. Even if the laws of the universe change on me, so that all my knowledge is void, I’ll just figure out the new laws, as has been done before. It’s not a Muggle thing, it’s a human thing, it just refines and trains the power you use every time you look at something you don’t understand and ask ‘Why?’”

belief and reality permalink

In chapter 22, Harry teaches Draco to apply scientific and rational methods to figure out why magic is becoming weaker. They consider the idea that magic is simply fading away:

“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.

the rational fear of death permalink

At one point in chapter 39, Dumbledore asks Harry why Dark Wizards feat death. What follows is a pretty great exposition on why we rationally fear death:

“Tell me Harry,” said the Headmaster (and now his voice sounded simply puzzled, though there was still a hint of pain in his eyes), “why do Dark Wizards fear death so greatly?”

“Er,” said Harry, “sorry, I’ve got to back the Dark Wizards on that one.”

… “What?” said Dumbledore.

“Death is bad,” said Harry, discarding wisdom for the sake of communication. “Very bad. Extremely bad. Being scared of death is like being scared of a great big monster with poisonous fangs. It actually makes a great deal of sense, and does not, in fact, indicate that you have a psychological problem.”

The Headmaster was staring at him as though he’d just turned into a cat.

… “It is not life they [the Dark Wizards] desire, but immortality; and they are so driven to grasp at it that they will sacrifice their very souls! Do you want to live forever, Harry?”

“Yes, and so do you,” said Harry. “I want to live one more day. Tomorrow I will still want to live one more day. Therefore I want to live forever, proof by induction on the positive integers. If you don’t want to die, it means you want to live forever. If you don’t want to live forever, it means you want to die. You’ve got to do one or the other… I’m not getting through here, am I.”

The two cultures stared at each other across a vast gap of incommensurability.

… “What would you do with eternity, Harry?”

Harry took a deep breath. “Meet all the interesting people in the world, read all the good books and then write something even better, celebrate my first grandchild’s tenth birthday party on the Moon, celebrate my first great-great-great grandchild’s hundredth birthday party around the Rings of Saturn, learn the deepest and final rules of Nature, understand the nature of consciousness, find out why anything exists in the first place, visit other stars, discover aliens, create aliens, rendezvous with everyone for a party on the other side of the Milky Way once we’ve explored the whole thing, meet up with everyone else who was born on Old Earth to watch the Sun finally go out, and I used to worry about finding a way to escape this universe before it ran out of negentropy but I’m a lot more hopeful now that I’ve discovered the so-called laws of physics are just optional guidelines.”

“I did not understand much of that,” said Dumbledore. “But I must ask if these are things that you truly desire so desperately, or if you only imagine them so as to imagine not being tired, as you run and run from death.”

“Life is not a finite list of things that you check off before you’re allowed to die,” Harry said firmly. “It’s life, you just go on living it. If I’m not doing those things it’ll be because I’ve found something better.”

In chapter 45, Harry destroys a Dementor, which was thought not to be possible. Being able to destroy a Dementor requires solving a riddle and knowing the what was really under the cloak, and Harry believes Godric Gryffindor had solved it.

It is a common misconception, thought Harry, that all the best rationalists are Sorted into Ravenclaw, leaving none for other Houses. This is not so; being Sorted into Ravenclaw indicates that your strongest virtue is curiosity, wondering and desiring to know the true answer. And this is not the only virtue a rationalist needs. Sometimes you have to work hard on a problem, and stick to it for a while. Sometimes you need a clever plan for finding out. And sometimes what you need more than anything else to see an answer, is the courage to face it…

The answer is that what is beneath the cloak of a Dementor is death. That is what inspires such great fear, that is why people often see dead bodies underneath the cloak, that is why Patronuses are animals (which aren’t aware of their own eventual death). Harry could not assuage his fear of death with another happy thought, so even his happiest thoughts couldn’t summon a Patronus. After understanding this, Harry returns to face the Dementor again:

Harry drew forth his wand that Professor Flitwick had returned to him, put his feet into the beginning stance for the Patronus Charm.

Within his mind, Harry discarded the last remnants of the peace of the phoenix, put aside the calm, the dreamlike state, remembered instead Fawkes’s piercing cry, and roused himself for battle. Called upon all the pieces and elements of himself to awaken. Raised up within himself all the strength that the Patronus Charm could ever draw upon, to put himself into the right frame of mind for the final warm and happy thought; remembered all bright things.

The books his father had bought him.

Mum’s smile when Harry had handmade her a mother’s day card, an elaborate thing that had used half a pound of spare electronics parts from the garage to flash lights and beep a little tune, and had taken him three days to make.

Professor McGonagall telling him that his parents had died well, protecting him. As they had.

Realizing that Hermione was keeping up with him and even running faster, that they could be true rivals and friends.

Coaxing Draco out of the darkness, watching him slowly move toward the light.

Neville and Seamus and Lavender and Dean and everyone else who looked up to him, everyone that he would have fought to protect if anything threatened Hogwarts.

Everything that made life worth living.

His wand rose into the starting position for the Patronus Charm.

Harry thought of the stars, the image that had almost held off the Dementor even without a Patronus. Only this time, Harry added the missing ingredient, he’d never truly seen it but he’d seen the pictures and the video. The Earth, blazing blue and white with reflected sunlight as it hung in space, amid the black void and the brilliant points of light. It belonged there, within that image, because it was what gave everything else its meaning. The Earth was what made the stars significant, made them more than uncontrolled fusion reactions, because it was Earth that would someday colonize the galaxy, and fulfill the promise of the night sky.

Would they still be plagued by Dementors, the children’s children’s children, the distant descendants of humankind as they strode from star to star? No. Of course not. The Dementors were only little nuisances, paling into nothingness in the light of that promise; not unkillable, not invincible, not even close. You had to put up with little nuisances, if you were one of the lucky and unlucky few to be born on Earth; on Ancient Earth, as it would be remembered someday. That too was part of what it meant to be alive, if you were one of the tiny handful of sentient beings born into the beginning of all things, before intelligent life had come fully into its power. That the much vaster future depended on what you did here, now, in the earliest days of dawn, when there was still so much darkness to be fought, and temporary nuisances like Dementors.

Mum and Dad, Hermione’s friendship and Draco’s journey, Neville and Seamus and Lavender and Dean, the blue sky and brilliant Sun and all bright things, the Earth, the stars, the promise, everything humanity was and everything it would become…

On the wand, Harry’s fingers moved into their starting positions; he was ready, now, to think the right sort of warm and happy thought.

And Harry’s eyes stared directly at that which lay beneath the tattered cloak, looked straight at that which had been named Dementor. The void, the emptiness, the hole in the universe, the absence of color and space, the open drain through which warmth poured out of the world.

The fear it exuded stole away all happy thoughts, its closeness drained your power and strength, its kiss would destroy everything that you were.

I know you now, Harry thought as his wand twitched once, twice, thrice and four times, as his fingers slid exactly the right distances, I comprehend your nature, you symbolize Death, through some law of magic you are a shadow that Death casts into the world.

And Death is not something I will ever embrace.

It is only a childish thing, that the human species has not yet outgrown.

And someday…

We’ll get over it…

And people won’t have to say goodbye any more…

The wand rose up and leveled straight at the Dementor.


The thought exploded from him like a breaking dam, surged down his arm into his wand, burst from it as blazing white light. Light that became corporeal, took on shape and substance.

A figure with two arms, two legs, and a head, standing upright; the animal Homo sapiens, the shape of a human being.

Glowing brighter and brighter as Harry poured all his strength into his spell, blazing with incandescent light brighter than the fading sunset, the Aurors and Professor Quirrell shielding their eyes in shock -

And someday when the descendants of humanity have spread from star to star, they won’t tell the children about the history of Ancient Earth until they’re old enough to bear it; and when they learn they’ll weep to hear that such a thing as Death had ever once existed!

The figure of a human shone more brilliant now than the noonday Sun, so radiant that Harry could feel the warmth of it on his skin; and Harry sent out all his defiance at the shadow of Death, opening all the floodgates inside him to make that bright shape blaze even brighter and yet brighter.

You are not invincible, and someday the human species will end you.

I will end you if I can, by the power of mind and magic and science.

I won’t cower in fear of Death, not while I have a chance of winning.

I won’t let Death touch me, I won’t let Death touch the ones I love.

And even if you do end me before I end you,

Another will take my place, and another,

Until the wound in the world is healed at last…

Harry lowered his wand, and the bright figure of a human faded away.

Slowly, he exhaled.

Like waking up from a dream, like opening his eyes after sleep, Harry’s gaze moved away from the cage, he looked around and saw that everyone was staring at him.

Albus Dumbledore was staring at him.

Professor Quirrell was staring at him.

The Auror trio was staring at him.

They were all looking at him like they’d just seen him destroy a Dementor.

The tattered cloak lay empty within the cage.

breaking patterns permalink

In a moment of anger in chapter 90, Harry tells Professor McGonagall that most people don’t hold themselves absolutely responsible for events around them. Instead, they play roles. “There’s a picture in your head of a stern disciplinarian and you do whatever that picture would do, whether or not it makes any sense. A stern disciplinarian would order the students back to their rooms, even if there was a troll roaming the hallways. A stern disciplinarian would order students not to leave the Hall on pain of expulsion. And the little picture of Professor McGonagall that you have in your head can’t learn from experience or change herself, so there isn’t any point to this conversation. People like you aren’t responsible for anything, people like me are, and when we fail there’s no one else to blame.”

But the lesson is that anyone can do it; anyone can break from these roles. Later, McGonagall uses this self-awareness to consciously change. Harry and Quirrell refer to this as her “going off-script”. It’s what brings her into her own when she becomes Headmistress of Hogwarts.

One of the most important plot drivers in the book is Hermione’s resistance to becoming Harry’s sidekick. She’s desperate to become a heroine in her own right, but at the same time she wonders if that’s really what she wants. In the end, Hermione learns that she doesn’t need to fit the mold of “sidekick” or even that of “heroine” to do the Good that she wants to do.

Chapter 122 ends the book the best way I could have possibly imagined. It perfectly resolves this tension, with the lesson that our utmost goal should be to Do Good, regardless of the patterns we break (or follow):

Hermione stood up from her cushion, and turned to face Harry. “I’m done with trying to be a heroine,” said Hermione Granger with the eastern sky brightening around her. “I shouldn’t ever have gone along with that entire line of thinking. There are just people who do what they can, whatever they can. And there are also people who don’t even try to do what they can, and yes, those people are doing something wrong. I’m not ever going to try to be a hero again. I’m not going to think in heroic terms if I can help it. But I won’t do any less than I can - or not a lot less, I mean, I’m only human.” Harry had never understood what was supposed to be mysterious about the Mona Lisa, but if he could have taken a picture of Hermione’s resigned/joyous smile just then, he had the sense that he could have looked at it for hours without understanding, and that Dumbledore could have read through it at a glance. “I won’t learn my lesson. I will be that stupid. I’ll go on trying to do most of what I can, or at least some of what I can - oh, you know what I mean. Even if it means risking my life again, so long as it’s worth the risk and isn’t being, you know, actually stupid. That’s my answer.” Hermione took a deep breath, but her face was resolute. “So, is there something I can do?”

Later, Hermione asks if they can finish their conversation about their relationship:

After a while, Hermione spoke. “Do you suppose we’ll fall in love with each other later on?”

“I don’t know any better than you do, Hermione. But why does it have to be about that? Seriously, why does it always have to be about that? Maybe when we’re older we’ll fall in love, and maybe we won’t. Maybe we’ll stay in love, and maybe we won’t. … No matter how it goes, we shouldn’t try to force our lives into a pattern. I think when people try to force patterns onto this sort of thing, that’s when they end up unhappy.”

“No forced patterns?” Hermione said. Her eyes had taken on a mischievous look. “That sounds like a more complicated way of saying no rules. Which I guess seems a lot more reasonable to me than it would’ve at the start of this year. If I’m going to be a Sparkling Unicorn Princess and have my own time machine, I might as well give up on rules, I suppose.”

“I’m not saying that rules are always bad, especially when they actually fit people, instead of them being blindly imitated like Quidditch. But weren’t you the one who rejected the ‘hero’ pattern in favor of just doing the things she could?”

“I suppose so. … You said, Harry, that you thought I was always destined to be the hero. I’ve been considering, and I suspect you’re completely wrong. If this had been meant to be, things would’ve been easier all round. Just doing the things you can do - you have to make that happen, you have to choose it, over and over again.”