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Harry Potter and the Methods of Rationality
The Methods of Rationality
2: HJPEV and the Professor's Games
3: HJPEV and the Shadows of Death
4: HJG and the Phoenix's Call
5: HJPEV and the Last Enemy
6: HJPEV and the Philosopher's Stone

Harry Potter and the Methods of Rationality

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.

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The Methods of Rationality

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?

Minerva: Magic.

Harry: Magic isn't enough to do that! You'd have to be a god!

—Harry's first encounter with magic

452 min read
Chapter 1: A Day of Very Low Probability
Chapter 2: Everything I Believe is False
Chapter 3: Comparing Reality To Its Alternatives
Chapter 4: The Efficient Market Hypothesis
Chapter 5: The Fundamental Attribution Error
Chapter 6: The Planning Fallacy
Chapter 7: Reciprocation
Chapter 8: Positive Bias
Chapter 9: Title Redacted, Part 1
Chapter 10: Self Awareness, Part II
Chapter 11: Omake Files 1, 2, 3
Chapter 12: Impulse Control
Chapter 13: Asking the Wrong Questions
Chapter 14: The Unknown and the Unknowable
Chapter 15: Conscientiousness
Chapter 16: Lateral Thinking
Chapter 17: Locating the Hypothesis
Chapter 18: Dominance Hierarchies
Chapter 19: Delayed Gratification
Chapter 20: Bayes's Theorem
Chapter 21: Rationalization
2: HJPEV and the Professor's Games

"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

349 min read
Chapter 22: The Scientific Method
Chapter 23: Belief in Belief
Chapter 24: Machiavellian Intelligence Hypothesis
Chapter 25: Hold Off on Proposing Solutions
Chapter 26: Noticing Confusion
Chapter 27: Empathy
Chapter 28: Reductionism
Chapter 29: Egocentric Bias
Chapter 30: Working in Group, Pt 1
Chapter 31: Working in Groups, Pt 2
Chapter 32: Interlude: Personal Financial Management
Chapter 33: Coordination Problems, Pt 1
Chapter 34: Coordination Problems, Pt 2
Chapter 35: Coordination Problems, Pt 3
Chapter 36: Status Differentials
Chapter 37: Interlude: Crossing the Boundary
3: HJPEV and the Shadows of Death

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.

478 min read
Chapter 38: The Cardinal Sin
Chapter 39: Pretending to be Wise, Pt 1
Chapter 40: Pretending to be Wise, Pt 2
Chapter 41: Frontal Override
Chapter 42: Courage
Chapter 43: Humanism, Pt 1
Chapter 44: Humanism, Pt 2
Chapter 45: Humanism, Pt 3
Chapter 46: Humanism, Pt 4
Chapter 47: Personhood Theory
Chapter 48: Utilitarian Priorities
Chapter 49: Prior Information
Chapter 50: Self Centeredness
Chapter 51: Title Redacted, Pt 1
Chapter 52: The Stanford Prison Experiment, Pt 2
Chapter 53: The Stanford Prison Experiment, Pt 3
Chapter 54: The Stanford Prison Experiment, Pt 4
Chapter 55: The Stanford Prison Experiment, Pt 5
Chapter 56: TSPE, Constrained Optimization
Chapter 57: TSPE, Constrained Cognition, Pt 7
Chapter 58: TSPE, Constrained Cognition, Pt 8
Chapter 59: TSPE, Curiosity, Pt 9
Chapter 60: The Stanford Prison Experiment, Pt 10
Chapter 61: TSPE, Secrecy and Openness, Pt 11
Chapter 62: The Stanford Prison Experiment, Final
Chapter 63: TSPE, Aftermaths
4: HJG and the Phoenix's Call

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?

522 min read
Chapter 64: Omake Files 4, Alternate Parallels
Chapter 65: Contagious Lies
Chapter 66: Self Actualization, Pt 1
Chapter 67: Self Actualization, Pt 2
Chapter 68: Self Actualization, Pt 3
Chapter 69: Self Actualization, Pt 4
Chapter 70: Self Actualization, Pt 5
Chapter 71: Self Actualization, Pt 6
Chapter 72: SA, Plausible Deniability, Pt 7
Chapter 73: SA, The Sacred and the Mundane, Pt 8
Chapter 74: SA, Escalation of Conflicts, Pt 9
Chapter 75: Self Actualization Final, Responsibility
Chapter 76: Interlude with the Confessor: Sunk Costs
Chapter 77: SA, Aftermaths: Surface Appearances
Chapter 78: Taboo Tradeoffs Prelude: Cheating
Chapter 79: Taboo Tradeoffs, Pt 1
Chapter 80: Taboo Tradeoffs, Pt 2, The Horns Effect
Chapter 81: Taboo Tradeoffs, Pt 3
Chapter 82: Taboo Tradeoffs, Final
Chapter 83: Taboo Tradeoffs, Aftermath 1
Chapter 84: Taboo Tradeoffs, Aftermath 2
Chapter 85: Taboo Tradeoffs, Aftermath 3, Distance
5: HJPEV and the Last Enemy

"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

...
285 min read
Chapter 86: Multiple Hypothesis Testing
Chapter 87: Hedonic Awareness
Chapter 88: Time Pressure, Pt 1
Chapter 89: Time Pressure, Pt 2
Chapter 90: Roles, Pt 1
Chapter 91: Roles, Pt 2
Chapter 92: Roles, Pt 3
Chapter 93: Roles, Pt 4
Chapter 94: Roles, Pt 5
Chapter 95: Roles, Pt 6
Chapter 96: Roles, Pt 7
Chapter 97: Roles, Pt 8
Chapter 98: Roles, Final
Chapter 99: Roles, Aftermath
6: HJPEV and the Philosopher's Stone

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 -

416 min read
Chapter 100: Precautionary Measures, Pt 1
Chapter 101: Precautionary Measures, Pt 2
Chapter 102: Caring
Chapter 103: Tests
Chapter 104: The Truth, Pt 1, Riddles and Answers
Chapter 105: The Truth, Pt 2
Chapter 106: The Truth, Pt 3
Chapter 107: The Truth, Pt 4
Chapter 108: The Truth, Pt 5, Answers and Riddles
Chapter 109: Reflections
Chapter 110: Reflections, Pt 2
Chapter 111: Failure, Pt 1
Chapter 112: Failure, Pt 2
Chapter 113: Final Exam
Chapter 114: Shut Up and Do The Impossible
Chapter 115: Shut Up and Do The Impossible, Pt 2
Chapter 116: Aftermath, Something to Protect, Pt 0
Chapter 117: Something to Protect: Minerva McGonagall
Chapter 118: Something to Protect: Professor Quirrell
Chapter 119: Something to Protect: Albus Dumbledore
Chapter 120: Something to Protect: Draco Malfoy
Chapter 121: Something to Protect: Severus Snape
Chapter 122: Something to Protect: Hermione Granger