Harry Potter and the Methods of Rationality (HPMOR) is a Harry Potter fan fiction by Eliezer Yudkowsky. It adapts the story of Harry Potter to explain complex concepts in cognitive science, philosophy, and the scientific method. Yudkowsky published HPMOR as a serial from February 28, 2010 to March 14, 2015, totaling 122 chapters and about 660,000 words. Yudkowsky wrote HPMOR to promote rationality skills he advocates on his community blog LessWrong. His reimagining supposes that Harry's aunt Petunia Evans married an Oxford professor and homeschooled Harry in science and rational thinking. As such, Harry "enters the wizarding world armed with Enlightenment ideals and the experimental spirit." The fan fiction spans one year, covering Harry's first year in Hogwarts. HPMOR has inspired other works of fan fiction, art, and poetry. Plot In this alternate universe, Lily Potter magically beautified Petunia Evans, letting her abandon Vernon Dursley and marry Oxford professor Michael Verres. They adopt Harry Potter as Harry James Potter-Evans-Verres, with him and Michael unaware of his heritage, and homeschool him in science and rationality. When Harry turns 11, Petunia and Professor McGonagall inform him and Michael about the wizarding world and Harry's defeat of Lord Voldemort. Harry becomes irritated over wizarding society's inconsistencies and backwardness. When boarding the Hogwarts Express, circumstances make Harry befriend Draco Malfoy over Ron Weasley. Harry also befriends Hermione Granger over their scientific inclinations. At Hogwarts, the Sorting Hat sends Hermione to Ravenclaw and Draco to Slytherin. Harry almost goes to Slytherin after a conversation with it, yet ultimately enters Ravenclaw. As school begins, Harry feels patronized by McGonagall and Headmaster Dumbledore, grows close with Professor Quirrell, and tests magic through the scientific method with Draco and Hermione. By testing timeless physics, Harry invents partial Transfiguration, a magical transmutation variant to transform parts of wholes. Quirrell starts a program involving "student armies" with Harry, Draco, and Hermione as first-year generals. After winter break, Quirrell procures a Dementor so students can learn the Patronus charm. Though Hermione and Harry initially fail, Harry recognizes Dementors as shadows of death. Resolving to defeat death, he invents the True Patronus charm and destroys the Dementor. After learning the regular Patronus, Draco discovers Harry can speak Parseltongue. Quirrell reveals himself as a snake Animagus to Harry and makes him help free Bellatrix Black from Azkaban, leaving her in hiding. Dumbledore learns about the prison break but not the participants, leading him