Harry Potter and the Methods of Rationality is a Harry Potter rational fanfic by Eliezer Yudkowsky, AI researcher and decision theorist. The book is also available in audiobook version here.
This is an Alternate Universe story, where Petunia married a scientist. Now Rationalist!Harry enters the wizarding world armed with Enlightenment ideals and the experimental spirit.
Cover art by DALL-E 2
Harry: You can't DO that!
Minerva McGonagall: It's only a transfiguration; an animagus transformation, to be exact—
Harry: You turned into a cat! A SMALL cat! You violated Conservation of Energy! That's not just an arbitrary rule – rejecting it destroys unitarity and then you get FTL signaling! And cats are COMPLICATED! How can you go on thinking using a cat-sized brain?
Harry: Magic isn't enough to do that! You'd have to be a god!
—Harry's first encounter with magic
"Hey, did you think going to the Moon was easy? Be glad this just involves changing your mind sometimes, and not a human sacrifice!"
"Human sacrifice would be way easier!"
There was a slight pause, and then the figure nodded. "Fair point."
- Harry and Draco discuss learning science
Professor Flitwick had silently passed Harry a folded parchment during Charms class that Monday, and the note had said that Harry was to visit the Headmaster at his convenience and in such fashion that no one else would notice, especially not Draco Malfoy or Professor Quirrell. His one-time password for the gargoyle would be "squeamish ossifrage". This had been accompanied by a remarkably artistic ink drawing of Professor Flitwick staring at him sternly, the eyes of which occasionally blinked; and at the bottom of the note, underlined three times, was the phrase DON'T GET INTO TROUBLE.
If you're five hours past your bedtime and still reading this, may I suggest getting some sleep? The fic will still be here tomorrow... unless, you know, something bad happens to it and the next morning there's just a 404 at this address and you're left with nothing but a fading memory and an eternal regret that you didn't stay awake longer and keep reading while you still had the chance... but hey, how probable is that?
"Is there some amazing rational thing you do when your mind's running in all different directions?" she managed.
"My own approach is usually to identify the different desires, give them names, conceive of them as separate individuals, and let them argue it out inside my head. So far the main persistent ones are my Hufflepuff, Ravenclaw, Gryffindor, and Slytherin sides, my Inner Critic, and my simulated copies of you, Neville, Draco, Professor McGonagall, Professor Flitwick, Professor
Harry stared at the bodies and tried to think. There was no time for doubts, for caveats, no brakes or second-guessing just take the first thoughts and run with them
In the back of Harry's mind, fragments of abstract thought flitted past, heuristics of problem-solving that there was no time to rehearse in words. In wordless flashes they shot past, to set up the object-level problem.
- the first place to look for a problem is whatever aspect of the situation seems most improbable
- simple explanations are more probable, eliminate separate improbabilities that must be postulated -
- what do I notice I am confused by -