Harry Potter and the Methods of Rationality

Harry nodded and continued. "So - suppose I had a way to get more Galleons from my vault without us going back to Gringotts, but it involved me violating the role of an obedient child. Would I be able to trust you with that, even though you'd have to step outside your own role as Professor McGonagall to take advantage of it?"

"What?" said Professor McGonagall.

"To put it another way, if I could make today have happened differently, so that we didn't take too little money with us, would that be all right even though it would involve a child being insolent to an adult in retrospect?"

"I... suppose..." the witch said, looking quite puzzled.

Harry took out the mokeskin pouch, and said, "Eleven Galleons originally from my family vault."

And there was gold in Harry's hand.

For a moment Professor McGonagall's mouth gaped wide, then her jaw snapped shut and her eyes narrowed and the witch bit out, "Where did you get that -"

"From my family vault, like I said."

"How?"

"Magic."

"That's hardly an answer!" snapped Professor McGonagall, and then stopped, blinking.

"No, it isn't, is it? I ought to claim that it's because I experimentally discovered the true secrets of how the pouch works and that it can actually retrieve objects from anywhere, not just its own inside, if you phrase the request correctly. But actually it's from when I fell into that pile of gold before and I shoved some Galleons into my pocket. Anyone who understands pessimism knows that money is something you might need quickly and without much warning. So now are you angry at me for defying your authority? Or glad that we succeeded in our important mission?"

The salesman's eyes were wide like saucers.

And the tall witch stood there, silent.

"Discipline at Hogwarts must be enforced," she said after almost a full minute. "For the sake of all the students. And that must include courtesy and obedience from you to all professors."

"I understand, Professor McGonagall."

"Good. Now let us buy that trunk and go home."

Harry felt like throwing up, or cheering, or fainting, or something. That was the first time his careful reasoning had ever worked on anyone. Maybe because it was also the first time he had something really serious that an adult needed from him, but still -

Minerva McGonagall, +1 point.

Harry bowed, and gave the bag of gold and the extra eleven Galleons into McGonagall's hands. "Thank you very much, Professor. Can you finish up the purchase for me? I've got to visit the lavatory."

The salesman, unctuous once more, pointed toward a door set into the wall with a gold-handled knob. As Harry started to walk away, he heard the salesman ask in his oily voice, "May I inquire as to who that was, Madam McGonagall? I take it he is Slytherin - third-year, perhaps? - and from a prominent family, but I did not recognise -"

The slam of the lavatory door cut off his words, and after Harry had identified the lock and pressed it into place, he grabbed the magical self-cleaning towel and, with shaky hands, wiped moisture off his forehead. Harry's entire body was sheathed in sweat which had soaked clear through his Muggle clothing, though at least it didn't show through the robes.

The sun was setting and it was very late indeed, by the time they stood again in the courtyard of the Leaky Cauldron, the silent leaf-dusted interface between magical Britain's Diagon Alley and the entire Muggle world. (That was one awfully decoupled economy...) Harry was to go to a phone box and call his father, once he was on the other side. He didn't need to worry about his luggage being stolen, apparently. His trunk had the status of a major magical item, something that most Muggles wouldn't notice; that was part of what you could get in the wizarding world, if you were willing to pay the price of a secondhand car.

"So here we part ways, for a time," Professor McGonagall said. She shook her head in wonderment. "This has been the strangest day of my life for... many a year. Since the day I learned that a child had defeated You-Know-Who. I wonder now, looking back, if that was the last reasonable day of the world."

Oh, like she had anything to complain about. You think your day was surreal? Try mine.

"I was very impressed with you today," Harry said to her. "I should have remembered to compliment you out loud, I was awarding you points in my head and everything."

"Thank you, Mr. Potter," said Professor McGonagall. "If you had already been sorted into a House I would have deducted so many points that your grandchildren would still be losing the House Cup."

"Thank you, Professor." It was probably too early to call her Minnie.