The One Thing I Can't Doubt Is That I Exist

He says the one thing I couldn't be fooled about if there were an evil demon who was trying to fool me about everything is that I exist. And this in the philosophical tradition is known as the cogito, cogito, ergo, sum, I think, therefore I am. So why does take up feel so certain that he exists? Because surely he could be dreaming that he exists. Even if he's dreaming, he exists. He has to exist in order to dream, to do anything, to work, to be in doubt, to be fooled by a demon, he has to exist. All these things are themselves, proofs in the moment of the fact that he existed.