Harry Potter and the Methods of Rationality

Nowadays it was called "blinding" and it was one of the things modern scientists took for granted. If you were doing a psychology experiment to see whether people got angrier when they were hit over the head with red truncheons than with green truncheons, you didn't get to look at the subjects yourself and decide how "angry" they were. You would snap photos of them after they'd been hit with the truncheon, and send the photos off to a panel of raters, who would rate on a scale of 1 to 10 how angry each person looked, obviously without knowing what color of truncheon they'd been hit with. Indeed there was no good reason to tell the raters what the experiment was about, at all. You certainly wouldn't tell the experimental subjects that you thought they ought to be angrier when hit by red truncheons. You'd just offer them 20 pounds, lure them into a test room, hit them with a truncheon, color randomly assigned of course, and snap the photo. In fact the truncheon-hitting and photo-snapping would be done by an assistant who hadn't been told about the hypothesis, so he couldn't look expectant, hit harder, or snap the photo at just the right time.

Blondlot had destroyed his reputation with the sort of mistake that would get a failing grade and probably derisive laughter from the T.A. in a first-year undergraduate course on experimental design... in 1991.

But this had been a bit longer ago, in 1904, and so it had taken months before Robert Wood had formulated the obvious alternative hypothesis and figured out how to test it, and dozens of other scientists had been sucked in.

More than two centuries after science had gotten started. That late in scientific history, it still hadn't been obvious.

Which made it entirely plausible that in the tiny wizarding world, where science didn't seem much known at all, no one had ever tried the first, the simplest, the most obvious thing that any modern scientist would think to check.

The books were full of complicated instructions for all the things you had to do exactly right in order to cast a spell. And, Harry had hypothesized, the process of obeying those instructions, of checking that you were following them correctly, probably did do something. It forced you to concentrate on the spell. Being told to just wave your wand and wish probably wouldn't work as well. And once you believed the spell was supposed to work a certain way, once you had practiced it that way, you might not be able to convince yourself that it could work any other way...

...if you did the simple but wrong thing, and tried to test alternative forms yourself.

But what if you didn't know what the original spell had been like?

What if you gave Hermione a list of spells she hadn't studied yet, taken from a book of silly prank spells in the Hogwarts library, and some of those spells had the correct and original instructions, while others had one changed gesture, one changed word? What if you kept the instructions constant, but told her that a spell supposed to create a red worm was supposed to create a blue worm instead?

Well, in that case, it had turned out...

...Harry was having trouble believing his results here...

...if you told Hermione to say "Oogely boogely" with the vowel durations in the ratio of 3 to 1 to 1, instead of the correct ratio of 3 to 1 to 2, you still got the bat but it wouldn't glow any more.

Not that belief was irrelevant here. Not that only the words and wand movements mattered.

If you gave Hermione completely incorrect information about what a spell was supposed to do, it would stop working.

If you didn't tell her at all what the spell was supposed to do, it would stop working.

If she knew in very vague terms what the spell was supposed to do, or she was only partially wrong, then the spell would work as originally described in the book, not the way she'd been told it should.

Harry was, at this moment, literally banging his head against the brick wall. Not hard. He didn't want to damage his precious brains. But if he didn't have some outlet for his frustration, he would spontaneously catch on fire.

Thud. Thud. Thud.

It seemed the universe actually did want you to say 'Wingardium Leviosa' and it wanted you to say it in a certain exact way and it didn't care what you thought the pronunciation should be any more than it cared how you felt about gravity.

WHYYYYYYYYYYYYYYYY?

The worst part of it was the smug, amused look on Hermione's face.

Hermione had not been okay with sitting around obediently following Harry's instructions without being told why.

So Harry had explained to her what they were testing.

Harry had explained why they were testing it.

Harry had explained why probably no wizard had tried it before them.

Harry had explained that he was actually fairly confident of his prediction.