Harry Potter and the Methods of Rationality

That is a really dumb idea, said Gryffindor. Even I think it's a dumb idea and I'm your Gryffindor side. You're not seriously going to just stand there and -

"We have a fix!" shouted Ora, holding up her magic mirror as though in triumph. "The Dementor outside the inner wall pointed to level seven, C spiral, that's where they are!"

Her Aurors were looking at her expectantly.

"No," Amelia said in a level voice. "That's where one of them is. The Dementors still can't find Bellatrix Black. We are not running down there and letting her through in the confusion, and we are not dividing our forces to be ambushed. So long as we move with caution, we can't lose. Tell Scrimgeour and Shacklebolt to keep going down level by level, same as before -"

The old wizard was already striding forward. Amelia didn't even bother cursing him, this time, as once again their carefully constructed shields parted like water and rippled gently in his wake.

Harry waited at the beginning of the corridor, just next to the stairs leading upward. Bellatrix and the snake were behind him, concealed by the Deathly Hallow that Harry had mastered; he knew, though he could not see, that the emaciated sorceress was sitting upon the stairs, slumped back, since Harry had withdrawn his Hover Charm to free up his mind and magic.

Harry's eyes were fixed on the far end of the corridor, next to the stairs that led downward. Not in his mind now, but in true reality, the light in the corridor had dimmed, the temperature had fallen. The fear thundered over him and around him like a sea whipped by hurricane winds, and the sucking emptiness had become a howling draw toward some approaching black hole.

Up the stairs at the far end, floating smoothly through the dying air, came the voids, the absences, the wounds in the world.

And Harry expected them to stop.

With all the will and focus he could muster, Harry expected them to stop.

Anticipated their stopping.

Believed they would stop.

...that was the idea, anyway...

Harry shut down the dangerous stray thought, and expected the Dementors to halt. They had no intelligence of their own, they were just wounds in the world, their form and structure was borrowed from others' expectations. People had been able to negotiate with them, offer them victims in exchange for cooperation, only because they believed Dementors would bargain. So if Harry believed hard enough that the voids would turn and go, they would turn and go.

But the wounds in the world kept coming, the swirling fear seemed like a solid thing now, the emptiness tearing at matter as well as mind, substance as well as spirit, you could see the metal beginning to tarnish as the holes in the world passed.

A small sound came from behind him, from Bellatrix, but she said no word, for she had been instructed to remain silent.

Don't think of them as creatures, think of them as psychosensitive objects, they can be controlled if I can control myself -

The problem was that he couldn't control himself so easily, couldn't make himself believe blue was green by an act of will. Couldn't suppress all those thoughts about how irrational it was to make yourself believe something. How impossible it was to trick yourself into believing something if you knew that was what you were doing. All the training Harry had given himself against self-deception was refusing to switch off no matter how harmful it was in this unique special case -

The shadows of Death crossed the halfway point of the corridor, and Harry held up his hand, fingers spread, and said in a voice of firm and confident command, "Stop."

The shadows of Death stopped.

Behind Harry, Bellatrix gave a strangled gasp, like it was being torn out of her.

Harry gestured to her, the signal he had set up in advance which meant, repeat what you heard the Dementors say.

"They say," Bellatrix said, her voice was shaking, "they said, 'Bellatrix Black was promised us. Tell us where she hides, and you will be spared.'"

"Bellatrix?" Harry said, making his voice sound amused. "She escaped a while ago."

A moment later, Harry realized that he should have said that Bellatrix was among the Aurors in the top level, that would have caused more confusion -

No, it was wrong to think of the Dementors as trickable, they were merely things, they were controlled only by expectations -

"They say," Bellatrix said in a cracked voice, "they say they know you're lying."

The voids began to move forward again.

Her anticipations are more solidly believed than mine; she is controlling them, unwittingly -

"Don't resist," Harry said, pointing his wand behind him.

"I, I love you, farewell, my Lord -"

"Somnium."

It had helped, strangely enough, hearing those particular awful words, understanding Bellatrix's mistake; it reminded Harry why he was fighting.

"Stop," Harry said again. Bellatrix was asleep; now only his own will, his own expectations rather, should