Eliezer Yudkowsky - Harry Potter and the Methods of Rationality

Professor McGonagall gave her students a sharp look. " Some teachers begin with Transfiguration Charms and move on to free Transfiguration afterwards. Yes, that would be much easier in the beginning. But it can set you in a poor mold which impairs your abilities later. Here you will learn free Transfiguration from the very start , which requires that you cast the spell wordlessly, by holding the subject form, the target form, and the transformation within your own mind."

"And to answer Mr. Potter's question," Professor McGonagall went on, "it is free Transfiguration which you must never do to any living subject. There are Charms and potions which can safely, reversibly transform living subjects in limited ways. An Animagus with a missing limb will still be missing that limb after transforming, for example. Free Transfiguration is not safe. Your body will change while it is Transfigured - breathing, for example, results in a constant loss of the body's stuff to the surrounding air. When the Transfiguration wears off and your body tries to revert to its original form, it will not quite be able to do so. If you press your wand to your body and imagine yourself with golden hair, afterwards your hair will fall out. If you visualise yourself as someone with clearer skin, you will be taking a long stay at St. Mungo's. And if you Transfigure yourself into an adult bodily form, then, when the Transfiguration wears off, you will die."

That explained why he had seen such things as fat boys, or girls less than perfectly pretty. Or old people, for that matter. That wouldn't happen if you could just Transfigure yourself every morning... Harry raised his hand and tried to signal Professor McGonagall with his eyes.

" Yes , Mr. Potter?"

"Is it possible to Transfigure a living subject into a target that is static, such as a coin - no, excuse me, I'm terribly sorry, let's just say a steel ball."

Professor McGonagall shook her head. "Mr. Potter, even inanimate objects undergo small internal changes over time. There would be no visible changes to your body afterwards, and for the first minute, you would notice nothing wrong. But in an hour you would be sick, and in a day you would be dead."

"Erm, excuse me, so if I'd read the first chapter I could have guessed that the desk was originally a desk and not a pig," Harry said, "but only if I made the further assumption that you didn't want to kill the pig, that might seem highly probable but -"

"I can foresee that marking your tests will be an endless source of delight to me, Mr. Potter. But if you have other questions can I please ask you to wait until after class?"

"No further questions, professor."

"Now repeat after me," said Professor McGonagall. "I will never try to Transfigure any living subject, especially myself, unless specifically instructed to do so using a specialised Charm or potion."

"If I am not sure whether a Transfiguration is safe, I will not try it until I have asked Professor McGonagall or Professor Flitwick or Professor Snape or the Headmaster, who are the only recognised authorities on Transfiguration at Hogwarts. Asking another student is not acceptable, even if they say that they remember asking the same question."

"Even if the current Defence Professor at Hogwarts tells me that a Transfiguration is safe, and even if I see the Defence Professor do it and nothing bad seems to happen, I will not try it myself."

"I have the absolute right to refuse to perform any Transfiguration about which I feel the slightest bit nervous. Since not even the Headmaster of Hogwarts can order me to do otherwise, I certainly will not accept any such order from the Defence Professor, even if the Defence Professor threatens to deduct one hundred House points and have me expelled."

"If I break any of these rules I will not further study Transfiguration during my time at Hogwarts."

"We will repeat these rules at the start of every class for the first month," said Professor McGonagall. "And now, we will begin with matches as subjects and needles as targets... put away your wands, thank you, by 'begin' I meant that you will begin taking notes."

Half an hour before the end of class, Professor McGonagall handed out the matches.

At the end of the class Hermione had a silvery-looking match and the entire rest of the class, Muggleborn or otherwise, had exactly what they'd started with.

Professor McGonagall awarded her another point for Ravenclaw.

After the Transfiguration class was dismissed, Hermione came over to Harry's desk as Harry was putting away his books into his pouch.

"You know," Hermione said with an innocent expression on her face, "I earned two points for Ravenclaw today."

"So you did," Harry said shortly.

"But that wasn't as good as your seven points," she said. "I guess I'm just not as intelligent as you."

Harry finished feeding his homework into the pouch and turned to Hermione with his eyes narrowed. He'd actually forgotten about that.

She batted her eyelashes at him. "We have lessons every day, though. I wonder how long it will take you to find some more Hufflepuffs to rescue? Today is Monday. So that gives you until Thursday."

The two of them stared into each other's eyes, unblinking.

Harry spoke first. "Of course you realise this means war."

"I didn't know we'd been at peace."

All of the other students were now watching with fascinated eyes. All of the other students, plus, unfortunately, Professor McGonagall.

"Oh, Mr. Potter," sang Professor McGonagall from the other side of the room, "I have some good news for you. Madam Pomfrey has approved your suggestion for preventing breakage in her Spimster wickets, and the plan is to finish the job by the end of next week. I'd say that deserves... let's call it ten points for Ravenclaw."

Hermione's face was gaping in betrayal and shock. Harry imagined his own face didn't look much different.

" Professor... " Harry hissed.

"Those ten points are unquestionably deserved, Mr. Potter. I would not hand out House points on a whim. To you it might have been a simple matter of seeing something fragile and suggesting a way to protect it, but Spimster wickets are expensive, and the Headmaster was not pleased the last time one broke." Professor McGonagall looked thoughtful. "My, I wonder if any other student has ever earned seventeen House points on his first day of lessons. I'll have to look it up, but I suspect that's a new record. Perhaps we should have an announcement at dinnertime?"

" PROFESSOR! " Harry shrieked. "This is our war! Stop meddling!"

"Now you have until Thursday of next week, Mr. Potter. Unless, of course, you engage in some sort of mischief and lose House points before then. Addressing a professor disrespectfully, for example." Professor McGonagall put a finger on her cheek and looked reflective. "I expect you'll hit negative numbers before the end of Friday."

Harry's mouth snapped shut. He sent his best Death Glare at McGonagall but she only seemed to find it amusing.

"Yes, definitely an announcement at dinner," Professor McGonagall mused. "But it wouldn't do to offend the Slytherins, so the announcement should be brief. Just the number of points and the fact of the record... and if anyone comes to you for help with their schoolwork and is disappointed that you haven't even started reading your textbooks, you can always refer them to Miss Granger."

" Professor! " said Hermione in a rather high-pitched voice.

Professor McGonagall ignored her. "My, I wonder how long it will take before Miss Granger does something deserving of a dinnertime announcement? I look forward to seeing it, whatever it may be."