# Learn dozens of rationality concepts...with the help of Harry Potter

December 2, 2015

Learning to improve your decision-making and sharpening your reasoning skills can prove tremendously beneficial. Unfortunately, some people find the heady concepts associated with improving this skill set — such as cognitive biases, statistical formulas, and the scientific method — a little dry and confusing. If you're one of these people, and especially if you've enjoyed J.K. Rowling's ubiquitous Harry Potter tales, we recommend checking out Harry Potter and the Methods Of Rationality, an elaborate piece of Harry Potter fan fiction that explains rationality-related ideas by inserting them into a hilarious reimagining of the epic Potter saga. It's an informative and extremely amusing read whether or not you've read the original series, and the whole thing is currently available for free online or as a downloadable PDF.

Written over the course of five years by AI researcher and rationalist Elizier Yudkowsky, who is perhaps best known for founding the Less Wrong rationality community, Harry Potter and the Methods Of Rationality is set in an alternate version of the Potter universe. In this altered timeline, Harry's aunt Petunia married an academic instead of the thick-witted Vernon Dursley of the original novels. Consequently, Harry grows up with a thoroughly scientific mindset and a decidedly smart-alecky attitude. HPATMOR follows this version of Harry as he applies his extensive toolkit of reasoning skills to the baffling logic of Rowling's wizarding world, often to chaotic and entertaining ends. Here's a sample from an early chapter in which Harry's worldview is upended by Professor McGonagall's decision to transform into a cat before his eyes:

"At once the small tabby cat morphed back up into a robed woman.

"I'm sorry, Mr. Potter," said the witch, sounding sincere, though the corners of her lips were twitching upwards. "I should have warned you."

Harry was breathing in short gasps. His voice came out choked. "You can't DO that!"

"It's only a Transfiguration," said Professor McGonagall. "An Animagus transformation, to be exact."

"You turned into a cat! A SMALL cat! You violated Conservation of Energy! That's not just an arbitrary rule, it's implied by the form of the quantum Hamiltonian! Rejecting it destroys unitarity and then you get FTL signalling! And cats are COMPLICATED! A human mind can't just visualise a whole cat's anatomy and, and all the cat biochemistry, and what about the neurology? How can you go on thinking using a cat-sized brain?""

HPATMOR isn't just entertaining; it's also a great educational resource. Over its sprawling 122-chapter run, the fiction illustrates dozens of valuable ideas from psychology, economics, philosophy, statistics, and many other fields tied to human rationality, from its early single-chapter explications of ideas like the Efficient Market Hypothesis and lateral thinking to extended explorations of more detailed concepts like humanism and the Stanford Prison Experiment. (It also touches on many subjects we've directly addressed here at ClearerThinking, including the Planning Fallacy and Bayes' Theorem.) Yudkowsky's writing is clear and amusing throughout — very few discussions of these perspective-altering notions are such joys to read.

This combination of ingredients has made HPATMOR extremely popular. Its conclusion in early 2015 was celebrated with real-world wrap parties in a number of cities, it's been reviewed on FanFiction.net some 31,000 times(!), and it's the subject of an extensive subReddit for fans that remains active today. And if you read it, it'll be easy to see why it's so well-loved; it's worth a look for anyone who's interested in bringing a scientific perspective to everyday life, Potter fan or no.