Dumbledore's question reminded Brian of an idea from a Muggle book he had read: humans had originally been foolish spirits drifting through the air, with memories so atrocious that their thoughts one second could be miles apart from their thoughts the next.
Humans back then had muddled through their existence, but enjoyed nearly infinite lifespans, until one day, a light bulb lit up above the head of an extraordinarily gifted human spirit-he awakened. Somehow, he remembered most of what had happened to him that day, and thought it was incredibly cool.
From that moment on, human spirits changed from pure spirits into combinations of spirit and flesh. The central idea was that human bodies had actually come into existence because spirits wanted to preserve their memories.
Judging by that Muggle book's logic, Quirrell, who had now lost all his memories, was already a different person from the previous Quirrell. By that reasoning, after pressing the "Memory Charm" button and restoring his factory settings, Quirrell should not be held responsible for what the old version of Quirrell had done.
However, that conclusion would only hold if Quirrell were the only person in the world, or if no one else had ever had any dealings with him. But humans had always been social animals.
That was an indisputable fact. Even if poets talked about human loneliness every day, people still shared certain collective memories, whether willingly or otherwise-for instance, the nursery rhyme "London Bridge Is Falling Down," or the fact that "Peeves always makes the floors of Hogwarts wet and slippery in winter."
Quirrell had been seen and recorded by others. A person who had existed in society was no longer simply himself, but a composite person made up of his own memories and those of others.
The sight of Harry hanging