The Best of Harry Potter and the Methods of Rationality

This weekend, the wildly popular fanfiction Harry Potter and the Methods of Rationality, written by Eliezer Yudkowsky, finally completed. With 122 chapters and around 650,000 words or 2,000 pages (over half as long as all seven of the original Harry Potter books combined), it's no walk in the park.

While I've encouraged many of my friends to pick up the series, the time involved should not be taken lightly. With that in mind, I thought I'd put together a highlight reel containing, in my opinion, the best stand-alone chapters and/or passages, without spoiling too much of the plot.

Thanks to my friends and fellow readers Ben Gunby, Megan Jackson and Timothy Johnson for some of the recommendations, as well as countless conversations about the chapters as we read them.

A brief introduction to HPMOR

The fanfiction is set in the Harry Potter universe, with a small number of changes that set the new plot into motion:

• Most prominently, instead of growing up under a staircase, Harry is raised as a child prodigy under the loving care of an Oxford professor of biochemistry. Through reading copious science and science fiction, Harry enters the wizarding world with most of a rationalist worldview and a rather big head. Yes, it matters immensely who Petunia Evans married.
• Professor Quirrell is transformed into an enigmatic and super awesome yet still sketchy Defense Against the Dark Arts teacher.
• Various other characters are strengthened, including major ones like Draco, Hermione, Dumbledore, and McGonagall. Some chapters are even written from Draco's perspective, making him into less of a stock character.
• The chapter titles describe the rationalist "lesson" being illustrated through the plot of those chapters (or sequences of chapters), such as "The Planning Fallacy" and "Belief in Belief."
• The entire plot takes place in Harry's first year at school.

Well, the last one is more of a result of the first, since as you'll see, some mysteries get resolved a whole lot quicker if you're actually rational.

I'll list the examples I want to share in the order they occur in the fanfic. For each, I'll trace out exactly what you should read by giving you search terms; if you search in your browser, you should be able to highlight the relevant search word for the ending, so you know where to stop. In most cases, what happens before and after is simply unrelated and won't spoil anything, but isn't the part that I'm trying to highlight.

Harry learns about the existence of magic

When Harry gets his Hogwarts acceptance letter, his adopted parents argue about whether magic is real, and Harry proposes a test: Bring a Hogwarts professor to demonstrate some magic for them.

Read: Chapter 2, "Everything I Believe is False," from the beginning to "escaped."

Hahaha, you can really see Harry's scientific background coming out here. No, I don't even know what FTL signalling is, though I have friends who do.

Besides using language like "updating on an event of infinitesimal probability," I identified with Harry when I first read this because it captures part of my reaction to reading plausible and even likely claims of present-day miracles (in books by Stafford and Metaxas in particular). What?!? These things are real? We thought we understood the world! It's also how I imagine most of my atheist friends reacting when I share these things with them.

I think we Christians don't realize the huge hurdle scientists, particularly physicists, need to get over before buying even the plausibility that miracles can happen. The program of determinism, breaking things down into smaller parts and understanding each of those smaller parts, is fundamentally at odds with the Christian theistic conception of a world where minds are basic entities.

But at the same time, Harry follows what he sees and immediately, while kicking and screaming, gives into the reality that magic exists. Would that a similar demonstration of power could win over today's real-life rationalists! Alas, miracles cannot be controlled in the same way magic can, which is where the analogy breaks down.

There's HUMoR too!

Wandering around Diagon Alley, Harry gets slightly frustrated by how many people recognize him and thank him for something he doesn't even remember doing. So when Harry gets fitted for robes, he decides to try the opposite trick on the other boy getting fitted with him. Little does he know...

Read: Chapter 5, "The Fundamental Attribution Error," from "shopfront" to the end.

If you're curious, the Fundamental Attribution Error is the error of attributing general, unchanging qualities to others based on events you see that are more often explained through circumstances. In Harry's case, people were giving him a "kills Dark Lords" character trait when he doesn't even remember doing it.

Harry and Hermione meet

McGonagall encourages Harry to find Hermione, which he does by asking if anyone knew the six quarks or where he could find her. When she names them, he knows who she is. Their ensuing conversation is exciting but bizarre, as two brilliant child prodigies meet and Harry immediately challenges Hermione's memory and wit. This puzzle is particularly insightful:

Read: Chapter 8, "Positive Bias," from "cylinder" to "euphoria."

Thus begins their great rivalry, which provides a lot of entertainment to the rest of the book and builds up two of the most best characters.

The Sorting Hat

When the Sorting Hat comes out, this time not all of the major characters end up in Gryffindor, as if it's the only house that matters. No, based on a scene on the train, Hermione and Neville end up where they really belong based on their character:

"Granger, Hermione!"

Hermione broke loose and ran full tilt towards the Sorting Hat, picked it up and jammed the patchy old clothwork down hard over her head, making Harry wince. Hermione had been the one to explain to him about the Sorting Hat, but she certainly didn't treat it like an irreplaceable, vitally important, 800-year-old artefact of forgotten magic that was about to perform intricate telepathy on her mind and didn't seem to be in very good physical condition.

"RAVENCLAW!"

And talk about your foregone conclusions. Harry didn't see why Hermione had been so tense about it. In what weird alternative universe would that girl not be Sorted into Ravenclaw? If Hermione Granger didn't go to Ravenclaw then there was no good reason for Ravenclaw House to exist.

Hermione arrived at the Ravenclaw table and got a dutiful cheer; Harry wondered whether the cheer would have been louder, or quieter, if they'd had any idea just what level of competition they'd welcomed to their table. Harry knew pi to 3.141592 because accuracy to one part in a million was enough for most practical purposes. Hermione knew one hundred digits of pi because that was how many digits had been printed in the back of her maths textbook.

Neville Longbottom went to Hufflepuff, Harry was glad to see. If that House really did contain the loyalty and camaraderie it was supposed to exemplify, then a Houseful of reliable friends would do Neville a whole world of good. Clever kids in Ravenclaw, evil kids in Slytherin, wannabe heroes in Gryffindor, and everyone who does the actual work in Hufflepuff.

So what happens when Harry is under the Hat? Well, it gets complicated...

Read: Chapter 10, all of it.

Beyond all of the Houses being strengthened into a worthwhile version of their character traits (rather than being just bystanders to a showdown between good Gryffindor and evil Slytherin), what I like about this chapter is that Harry is forced to wrestle with the importance of ambition. He's consumed by the fear that he'll become just another child prodigy that flashes and fades. I'd be lying if I said I haven't given that some thought as my own ambition has died a slow death.

Also, you gotta admit, having your thoughts read and conducting a conversation that way is pretty mind-bendingly awesome.

The Chamber of Secrets

The passage I wanted to highlight here is so short (in Chapter 14) that I'll just block-quote it. It also happens to entirely resolve the plot of the original second Harry Potter book. Once Professor McGonagall realizes that Harry can speak Parseltongue...

"I... see," Professor McGonagall said. "And if, perhaps, you were to discover the entrance to Salazar Slytherin's legendary Chamber of Secrets, an entrance that you and you alone could open..."

"I would close the entrance and report to you at once so that a team of experienced magical archaeologists could be assembled," Harry said promptly. "Then I would open up the entrance again and they would go in very carefully to make sure that there was nothing dangerous. I might go in later to look around, or if they needed me to open up something else, but it would be after the area had been declared clear and they had photographs of how everything looked before people started tromping around their priceless historical site."

Professor McGonagall sat there with her mouth open, staring at him like he'd just turned into a cat.

"It's obvious if you're not a Gryffindor," Harry said kindly.

"I think," Professor McGonagall said in a rather choked voice, "that you far underestimate the rarity of common sense, Mr. Potter."

Well, that settles it! Next book?

Using a Time Turner to Prove P=NP

Harry gets a Time-Turner from Professor McGonagall to correct a problem with his sleep where he operates regularly on a 26-hour day. Of course, he immediately has one of those "you just turned into a cat" moments upon realizing this. A while later, he tries to see what the Time Turner can really do...

Read: Chapter 17, "Locating the Hypothesis," beginning to "scariest."

If you're confused, or it's been a while since you read the third Harry Potter book, let me explain how Time Turners in the Harry Potter universe work: Whatever happens as a result of individuals using Time Turners, the universe somehow magically turns out to be consistent with itself. The author adds, "in the simplest way possible" in a later chapter. This renders our usual notions of causality and even free will obsolete, because causal arrows can point backwards in time, and individuals' wills are constrained to make the universe consistent (e.g. Harry writing exactly the same message that he had already read).

In this particular test, Harry attacks a famous problem, wondering if a computer (himself) with a time turner could do things that we fundamentally believe computers today can't do. (Though we haven't proven that they can't yet; this is the famous "P=NP" problem.) Having access to such a supercomputer, essentially, could dramatically change basically anything that uses a computer.

Studying Magic Like a Scientist

How would a scientist approach magic? Harry, as the child prodigy magical scientist wannabe, was about to find out.

Read: Chapter 22, "The Scientific Method," "stained" to "AAAAAAAAAAAAAAHHHHHHHHHHHHHHH."

What went wrong here? Well, Harry is frustrated because his first hypothesis didn't turn out to be true. But the story is clear: This magical world is not incomprehensible. The way Hermione pronounces things, and her own beliefs about what she's saying, affect the result in a consistent way. It just doesn't work the way Harry expects.

I have a similar hope for investigating claims of miracles. Some people propose that it might be anti-inductive, in that God might not desire to be known, but thankfully that's not the God that the Bible presents. By no means will it be easy, though, like Harry's research project.

The Best Addition (In My Opinion): Battles

The new and improved Professor Quirrell declares that the usual classroom time is not enough to catch them up on everything they need to learn in his class, which he renames "Battle Magic." No, you need real-world experience.

Read: Chapters 30 and 31, "Working in Groups." You can ignore the part about the marshmallow.

I don't have a lot to say about this besides that I really enjoyed it. It's like an action movie, made more exciting by the personal dynamics involved. My favorite part of the story, and this is just the beginning. Chapter 33 is another spoiler-free battle chapter with an epic finish if you're curious, but I won't make another section for it.

Dueling with Mad-Eye Moody

For a taste of the tone later on, in chapter 86 (of 122), Mad-Eye Moody visits Hogwarts to discuss what has been going on with Dumbledore, McGonagall and Harry Potter. Harry objects to a plan they were discussing (not of particular importance) and Moody challenges him: Hit me with a spell to get the right to contradict me.

Read: Chapter 86, "Multiple Hypothesis Testing," from "trainee" to "cleverness." Be careful around the endpoints of this one.

This is sort of like an action scene to me; it's awesome to me to see how Time Turners and Harry's cloak come into play in the duel, and even then they're not enough. And it makes the duel a fascinating puzzle you could sort of try to figure out along with Harry.

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There's a lot more I wish I could include, but too many scenes have spoilers (often as short as phrases like "ever since..."), especially later on in the book. If this tasting inspires you to read more, feel free to pick it up for yourself in your spare time!