Harry Potter and the Methods of Rationality

That Father had been expecting Draco to tell Harry Potter exactly that was not something Draco said out loud. Harry Potter would work it out on his own, or not.

But instead Harry Potter shook his head, smiling beneath the cowl. "I have no intention of trying to quash Rita Skeeter."

Draco didn't even try to keep the incredulity out of his voice. "You can't tell me you don't care what the newspaper says about you!"

"I care less than you might think," said Harry Potter. "But I have my own ways of dealing with the likes of Skeeter. I don't need Lucius's help."

A worried look came over Draco's face before he could stop it. Whatever Harry Potter was about to do next, it would be something Father wasn't expecting, and Draco was feeling very nervous about where that might lead.

Draco also realized that his hair was getting sweaty underneath the cowl. He'd never actually worn one of those before, and hadn't realized that the Death Eaters' cloaks probably had things like Cooling Charms.

Harry Potter wiped some sweat from his forehead again, grimaced, took out his wand, pointed it upward, took a deep breath, and said "Frigideiro!"

Moments later Draco felt the cold draft.

"Frigideiro! Frigideiro! Frigideiro! Frigideiro! Frigideiro!"

Then Harry Potter lowered the wand, though his hand seemed a bit shaky, and put it back into his robes.

The whole room seemed perceptibly cooler. Draco could have done that too, but still, not bad.

"So," Draco said. "Science. You're going to tell me about blood."

"We're going to find out about blood," Harry Potter said. "By doing experiments."

"All right," Draco said. "What sort of experiments?"

Harry Potter smiled evilly beneath his cowl, and said, "You tell me."

Draco had heard of something called the Socratic Method, which was teaching by asking questions (named after an ancient philosopher who had been too smart to be a real Muggle and hence had been a disguised pureblood wizard). One of his tutors had used Socratic teaching a lot. It had been annoying but effective.

Then there was the Potter Method, which was insane.

To be fair, Draco had to admit that Harry Potter had tried the Socratic Method first and it hadn't been working too well.

Harry Potter had asked how Draco would go about disproving the blood purist hypothesis that wizards couldn't do the neat stuff now that they'd done eight centuries ago because they had interbred with Muggleborns and Squibs.

Draco had said that he did not understand how Harry Potter could sit there with a straight face and claim this was not a trap.

Harry Potter had replied, still with a straight face, that if it was a trap it would have been so pathetically obvious that he ought to be ground up and fed to pet snakes, but it was not a trap, it was simply a rule of how scientists operated that you had to try to disprove your own theories, and if you made an honest effort and failed, that was victory.

Draco had tried to point out the staggering stupidity of this by suggesting that the key to surviving a duel was to cast Avada Kedavra on your own foot and miss.

Harry Potter had nodded.

Draco had shaken his head.

Harry Potter had then presented the idea that scientists watched ideas fight to see which ones won, and you couldn't fight without an opponent, so Draco needed to figure out opponents for the blood purist hypothesis to fight so that blood purism could win, which Draco understood a little better even though Harry Potter had said it with a rather distasteful look. Like, it was clear that if blood purism was the way the world really was, then the sky just had to be blue, and if some other theory was true, the sky just had to be green; and nobody had seen the sky yet; and then you went outside and looked and the blood purists won; and after this had happened six times in a row, people would start noticing the trend.

Harry Potter had then proceeded to claim that all the opponents Draco was inventing were too weak, so blood purism wouldn't get credit for defeating them because the battle wouldn't be impressive enough. Draco had understood that too. Wizards have gotten weaker because house elves are stealing our magic hadn't sounded impressive to him either.

(Though Harry Potter had said that one at least was testable, in that they could try to check if house elves had gotten stronger over time, and even draw a picture representing the increasing strength of house elves and another picture representing the decreasing strength of wizards and if the two pictures matched that would point to the house elves, all said in such completely serious tones that Draco had felt an impulse to ask Dobby a few pointed questions under Veritaserum before snapping out of it.)

And Harry Potter had finally said that Draco couldn't fix the battle, scientists weren't dumb, it would be obvious if you fixed the battle, it had to be a real fight, between two different theories that might both really be true, with a test that only the true hypothesis would win, something that actually would come out different ways depending on which hypothesis was actually correct, and there would be experienced scientists watching to make sure that was exactly what happened. Harry Potter had claimed that he himself just wanted to know how blood really worked and for that he need to see blood purism really win and Draco wasn't going to fool him with theories that were just there to be knocked down.

Even having seen the point, Draco hadn't been able to invent any "plausible alternatives", as Harry Potter put it, to the idea that wizards were getting less powerful because they were mixing their blood with mud. It was too obviously true.