Harry Potter and the Methods of Rationality

"Point of order," said Harry's voice. "I know the Defense Professor is watching, but I still have to ask, does anyone know whether they'll slice each other in half if they actually hit -"

"No," Hermione said absently. This had been in one of her history books, though she'd had no idea the magical dueling sword looked like that. "They cast it so it'll only stun if it touches."

"You know that spell?"

"Oh, no, it's the Charm of the Most Ancient Blade, it's only legal for Noble and Most Ancient Houses to use -"

Hermione stopped talking and looked at Harry, or Harry's grey hood rather.

"Well," said Harry's voice, "I guess I could take down the rest of the Sunshine Regiment by myself, then." She couldn't see his face, but his voice sounded like he was smiling.

"You dodged when Daphne hit your own spell back at you," Hermione said. "So whatever you did, you're not invincible. A Stupefy can still get you."

"Interesting theory," said Harry's voice from beneath the hood. "Got anyone in your army who can test it?"

"I read about the Stunning Hex once," said Hermione. "A few months ago. I wonder if I can remember the instructions right?" Her wand came up to point at Harry.

There was a slight pause, as nearby a boy and a girl breathing in audible gasps slowly whacked at each other with lightsabers.

"Of course," Harry said, leveling his own wand on her, "I can just use Somnium on you. That'll take a lot less effort."

New Contego shields sprung into existence in front of her, cast by Jenny and Parvati, even as Harry spoke.

The tip of Hermione's own wand began making small motions in the air, a diamond within a circle, a diamond within a circle, rehearsing the gesture to match exactly what she remembered seeing in the book. It would be a difficult feat even for her, but she had to cast the spell right on the first try, she couldn't afford any failed castings that would sap her energy.

"You know," said Hermione Granger, "I understand that it's not really your fault, but I'm getting tired of hearing people talk about the Boy-Who-Lived like you're - like you're some kind of god or something."

"Same here, I must say," said Harry Potter. "It's sad how people keep underestimating me."

Her wand kept rehearsing the diamond within the circle, over and over. Harry would be recharging his own strength, she knew, even as she practiced as much as she could before her attack. "I'm starting to think you need taking down a peg, General Chaos."

"You could be right," Harry said equably. His feet began to shuffle through what she recognized as a duelist's dance. "Unfortunately there's nothing left that can defeat me now except another Harry Potter."

"Let me be specific, Mr. Potter. I'm taking you down a peg."

"You and what other army?"

"You think you're pretty cool, don't you," said Hermione.

"Why, yes," said Harry. "Yes, I do. Some might call that arrogant, but am I supposed to be the last person in Hogwarts to notice how awesome I am?"

Hermione raised her left hand into the air, and made a fist.

It was a signal. Eight designated soldiers in her army would be pointing their wands at her, and quietly casting Wingardium Leviosa.

They'd practiced this, too, once Hermione had given up on lecturing her soldiers, and at Anthony's suggestion, tried giving them a Sunshine General who looked like she could defeat invincible enemies.

"You pretend you're Superman," said Hermione. She raised her left fist higher in the air, and the eight soldiers supporting her Hovered her off the ground. "Well here's Super Hermione!" Her hand pushed forward, and as she shot rapidly through the air toward Harry, regretting only that she couldn't see the look on his face, her wand made a diamond within a circle and she summoned up all the magic she could, it felt like she imagined touching a live wire would feel as the too-powerful spell poured through her when her voice screamed "Stupefy!"

The red bolt burst from her wand, perfectly formed.

Harry dodged it.

And then, because they hadn't practiced doing this part inside of hallways, she crashed into a wall.

"Somnium!" shrieked Draco, and then after only a few seconds to recharge, "SOMNIUM, CURSE YOU!"

He knew he was hitting Theodore, the other boy wasn't even trying to dodge, but the scion of Nott only grinned as evilly as his father and leveled his wand -

Draco managed to leap aside just as Theodore said "Somnium!" but Draco was getting winded, he couldn't keep this up, Theodore wasn't bothering to dodge at all while Draco had to keep moving, this was crazy.

He had enough strength now to fire again, but -

Stupidity is doing the same thing and expecting a different result, Harry had said, this was Harry's work somehow, it couldn't be a Muggle artifact anymore but Draco couldn't figure out what it could be, and he should be thinking of hypotheses and ways to test them but he was too busy frantically dodging as Theodore laughed and shot another Sleep Hex at him, Draco felt a