Harry Potter and the Methods of Rationality

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.