Summary: One of the most intensely fascinating parts of the Harry Potter series has been the Sorting Hat, which can never seem to be truly explained. This topic leaves fans plenty of room for our minds to wander freely and for us to form our own opinions. What really is the Sorting Hat? How could it be an ordinary piece of clothing when it has so much brain power, and has been sorting students into their correct houses for a thousand years?
"Twas Gryffindor who found the way,
He whipped me off his head
The founders put some brains in me
So I could choose instead!"
Excerpt of song from Goblet of Fire
The sorting hat clearly seems to have started out as a normal hat. He, or she, as gender is never specified, started as a plain inanimate object. It was really nothing more then a hat that sat on Gryffindor's head until the time came that it was needed to do its duty for the founders. How could the sorting hat make such a huge jump from ordinary hat to a extraordinary all-knowing-gives-warnings-in-grave-peril hat? It says that "the founders put some brains in me so I could choose instead." Yet how was this done?
Is the sorting hat alive? For it certainly can hear and speak like a living being. This seems almost similar to Transfiguration, the same kind of magic that changes desks into pigs. It should be, from normal rules stated even in the books, impossible for a wizard to create life. Could the sorting hat be a bit of clever Transfiguration to turn a hat into a human-like life form?
But this doesn't seem right, in a way, to me. It isn't a person, as much as it acts like one. It is still a hat, and it takes all its chances to say this to us. It seems like just a bit of clever charmwork, a hat that is capable of human speech and hearing, as well as legilimency. It seems like an immensely complicated charm, because what else could it be? As J.K. Rowling has said in the Sorting Hat Chapter on her Pottermore site, "It literally contains the intelligence of the four founders, can speak (through a rip near its brim) and is skilled at Legilimency, which enables it to look into the wearer's head and divine his or her capabilities or mood. It can even respond to the thoughts of the wearer." It seems to me that when it first started out, it was a hat with no memories or knowledge. As charms were put on it, suddenly it could hear and think. As it sat around the most powerful magicians of the age, it started hearing things. As it sat on the founders heads it gained their knowledge. With nothing to do but listen and think, the sorting hat sits all year in the headmasters office, picking up bits and pieces of important information and stringing it all together. Every year it sits on dozens of students heads getting all their memories and feelings. When the years went on, and its creators died, the Sorting hat became a Frankenstein-esque creation. It soon understood the world more then most of the humans alive. If we assume that it's memory is good, the hat likely knows as much information as every human head it ever sat apon, and everything it ever heard as it rested in one of the most powerful rooms in the wizarding world.