by Julia Galef
If you wanted to teach people about science, you probably wouldn’t set out to write a 
Harry Potter and the Methods of Rationality isn’t primarily interested in teaching readers the “what” of science, even though it is liberally sprinkled with interesting facts about genetics, game theory, quantum mechanics, and psychology, among other things. Instead, as the title suggests, it’s about the “how” of science, conceived of not in the narrow sense of research in a laboratory, but in the broader sense of the process of figuring out how anything in the world works.
Like his counterpart in the original series, this Harry Potter is a seemingly ordinary British boy who is thrust into the magic world at the age of eleven. But unlike the mistreated waif of the original series, this Harry has grown up with caring, intellectual parents who bought him all the books he wanted and encouraged his analytic instincts. So when he finds himself plunged into a new, magical world, he immediately starts using that training to find the answers to a host of new questions that confront him: Who can I trust? Why are some people able to do magic and others not? Is there an afterlife? What are ghosts? And how does magic actually work?
Magic may not operate by the logic we’re used to in our world, Harry reasons, but it must operate by some logic. His attempts to methodically figure out what that is are some of the most intellectually enjoyable parts of the series. For example, it appears that you can cause a target to levitate by uttering the magic phrase “Wingardium Leviosa.” But what’s doing the actual work: the sounds made by the spellcaster’s mouth, or the concept in the spellcaster’s head?
Harry’s hypothesis is that the pronunciation of the words can’t possibly be the “active ingredient” in the spell: “You couldn’t really need to say ‘Wingardium Leviosa’ in exactly the right way in order to levitate something,” Harry thinks, “because, come on, ‘Wingardium Leviosa’? The universe was going to check that you said ‘Wingardium Leviosa’ in exactly the right way and otherwise it wouldn’t make the quill float? No. Obviously no…”
The way he goes about testing rival hypotheses is a case study in clever experimental design. He gives his friend Hermione a list of real spells she’s never seen before, asking her to learn and attempt to cast them. Some of the spells have been slightly altered in either the spellcasting phrase they prescribe, or the intended result; others are unchanged (the control group). Voila: a blind study testing for whether correct pronunciation and/or mental concept are crucial to a spell’s power.
In fact, it’s only after watching Harry attempt to figure out how magic works that it begins to seem strange that in most fantasy novels, people are willing to accept “Magic” as a complete explanation of how things work in their world. It’s an empty explanation, Harry protests to his teacher Professor McGonagall: “‘That’s just a word! Even after you tell me that, I can’t make any new predictions! It’s exactly like saying ‘phlogiston’ or ‘elan vital’…”
Harry is referencing scientific “theories” purporting to explain heat and life, respectively, which in retrospect we now recognize to be as empty as “magic.” What makes some things alive and others not? A life-giving essence called “élan vital,” suggested early 20th century scientists. And what is élan vital? Well, it’s something that causes life.
The circularity stems from the fact that “élan vital” isn’t actually an answer – it’s just a new name for “whatever causes life,” the mechanisms of which remain just as unknown to us regardless of what we call them. In other words, Harry is arguing, if your theory doesn’t generate any new predictions about the world – predictions about what evidence you would expect to see if your theory were true, but not if your theory were false – then it’s not a real theory.
Since scientific thinking hasn’t been a priority in the wizarding world, Harry has a huge competitive edge. That’s somewhat mitigated, however, by the fact that he frequently ends up mired in arguments with less rational wizards. Hogwarts headmaster Dumbledore, for example, serves as a poster child for the fact that “wisdom” without critical thinking isn’t wisdom at all. When he offers Harry a platitude about how death is just the beginning of a great new adventure, the two of them end up in a heated argument about the existence of an afterlife.
“And how does anyone know that? … Don’t tell me what you believe, tell me what you’ve seen,’” Harry demands. Dumbledore tells him about a stone archway called the Veil, a gateway to the next world; those standing near it can hear the whispers of dead souls on the other side. Spooky, sure, but – as Harry points out – what is the most likely explanation for the archway? That there exists another world of disembodied minds which can be contacted through an archway? Or that someone charmed the archway so that it would whisper and hypnotize passersby? Which of those two explanations seems more plausible given our prior knowledge of the world?
There’s also the Resurrection Stone, counters Dumbledore, an old artifact which seems to have the power to bring back spirits of the deceased. But again, Harry says, that’s jumping to conclusions about what’s actually happening. An alternative hypothesis instead of “This stone brings back dead people” is that the stone merely generates a material projection from the user’s memories of the deceased. “The obvious test to see if the Resurrection Stone is really calling back the dead, or just projecting an image from the user’s mind, is to ask a question whose answer you don’t know, but the dead person would, and that can be definitely verified in this world,” Harry says. For example, call back your dead wife and ask her where she left her lost earring.
It’s a cerebral series, to be sure, but it’s far from bloodless. The hypothesis testing and discussions of rationality grow organically out of a fast-paced plot with dramatic highs and lows, and in which the eeriest lurking threat isn’t the Dark Lord Voldemort, but the possibility that Harry himself could turn into a dark lord. And the only thing more dangerous than an evil villain? An evil villain with an unparalleled training in rationality.