Harry Potter and the Methods of Rationality

Harry nodded decisively. "That's one." He wrote it down on the parchment under Tests:

A. Are there spells we know but can't cast (1 or 2) or are the lost spells no longer known (3)?

"So that distinguishes between 1 and 2 on the one hand, and 3 on the other hand," said Harry. "Now we need some way to distinguish between 1 and 2. Magic fading, blood weakening, how could we tell the difference?"

"What kind of Charms did students used to cast in their first year at Hogwarts?" said Draco. "If they used to be able to cast much more powerful Charms, the blood was stronger -"

Harry Potter shook his head. "Or magic itself was stronger. We have to figure out some way of telling the difference." Harry stood up from his chair, began pacing nervously through the classroom. "No, wait, that might still work. Suppose different spells use up different amounts of magical energy. Then if the ambient magic weakened, the powerful spells would die first, but the spells everyone learns in their first year would stay the same..." Harry's nervous pacing sped up. "It's not a very good test, it's more about powerful wizardry being lost versus all wizardry being lost, someone's blood could be too weak for powerful wizardry but strong enough for easy spells... Draco, do you know if more powerful wizards within a single era, like powerful wizards from just this century, are more powerful as children? If the Dark Lord had cast the Cooling Charm when he was eleven, could he have frozen the whole room?"

Draco's face screwed up as he tried to recollect. "I can't remember hearing anything about the Dark Lord but I think Dumbledore's supposed to have done something amazing on his Transfiguration O.W.L.s in fifth year... I think other powerful wizards were good in Hogwarts too..."

Harry scowled, still pacing. "They could just be studying hard. Still, if first-year students learned the same spells and seemed about as powerful then as now, we could call that weak evidence favoring 1 over 2... wait, hold on." Harry stopped where he stood. "I have another test that might distinguish between 1 and 2. It would take a while to explain, it uses some things that scientists know about blood and inheritance, but it's an easy question to ask. And if we combine my test and your test and they both come out the same way, that's a strong hint at the answer." Harry almost ran back to the desk, took the parchment and wrote:

B. Did ancient first-year students cast the same sort of spells, with the same power, as now? (Weak evidence for 1 over 2, but blood could also be losing powerful wizardry only.)

C. Additional test that distinguishes 1 and 2 using scientific knowledge of blood, will explain later.

"Okay," said Harry, "we can at least try to tell the difference between 1 and 2 and 3, so let's go with this right away, we can figure out more tests after we do the ones we already have. Now it's going to look a little odd if Draco Malfoy and Harry Potter go around asking questions together, so here's my idea. You'll go through Hogwarts and find old portraits and ask them about what spells they learned to cast during their first years. They're portraits so they won't know there's anything odd about Draco Malfoy doing that. I'll ask recent portraits and living people about spells we know but can't cast, no one will notice anything unusual if Harry Potter asks weird questions. And I'll have to do complicated research about forgotten spells, so I want you to be the one to gather the data I need for my own scientific question. It's a simple question and you should be able to find the answer by asking portraits. You might want to write this down, ready?"

Draco sat down again and scrabbled in his bookbag for parchment and quill. When it was laid down on the desk, Draco looked up, face determined. "Go ahead."

"Find portraits who knew a married Squib couple - don't make that face, Draco, it's important information. Just ask recent portraits who are Gryffindors or something. Find portraits who knew a married Squib couple well enough to know the names of all their children. Write down the name of each child and whether that child was a wizard, a Squib, or a Muggle. If they don't know whether the child was a Squib or a Muggle, write down 'non-wizard'. Write that down for every child the couple had, don't leave any out. If the portrait only knows the name of the wizarding children, not the names of all the children, then don't write down any data from that couple. It's very important that you only bring me data from someone who knows all the children a Squib couple had, well enough to know them all by name. Try to get at least forty names total, if you can, and if you have time for more, even better. Have you got all that?"

"Repeat it," Draco said, when he was done writing, and Harry repeated it.

"I've got it," Draco said, "but why -"

"It has to do with one of the secrets of blood that scientists already discovered. I'll explain when you get back. Let's split up and meet back here in an hour, 6:22pm that should be. Are we ready to go?"

Draco nodded decisively. It was all very rushed, but he'd long since been taught how to rush.

"Then go!" said Harry Potter and yanked off his cowled cloak and shoved it into his pouch, which began eating it, and, without even waiting for his pouch to finish, spun around and began striding rapidly toward the classroom door, bumping into a desk and almost falling over in his haste.

By the time Draco had managed to get his own cloak off and stow it in his bookbag, Harry Potter was gone.

Draco almost ran out the door.

Chapter 23: Belief in Belief

Everybody wants a rock to wind a piece of string around J. K. Rowling.

"And then Janet was a Squib," said the portrait of a short young woman with a gold-trimmed hat.

Draco wrote it down. That was only twenty-eight but it was time to go back and meet Harry.

He'd needed to ask other portraits to help translating, English had changed a lot, but the oldest portraits had described first-year spells that sounded an awful lot like the ones they had now. Draco had recognized around half of them and the other half didn't sound any more powerful.

The sick feeling in his stomach had grown with each answer until finally, unable to take it any more, he'd gone off and asked other portraits Harry Potter's strange question about Squib marriages, instead. The first five portraits hadn't known anyone and finally he'd asked those portraits to ask their acquaintances to ask their acquaintances and so managed to find some people who'd actually admit to