The Meditator reflects that he has often found himself to be mistaken with regard to matters that he formerly thought were certain, and resolves to sweep away all his pre-conceptions, rebuilding his knowledge from the ground up, and accepting as true only those claims which are absolutely certain. All he had previously thought he knew came to him through the senses. Through a process of methodological doubt, he withdraws completely from the senses. At any moment he could be dreaming, or his senses could be deceived either by God or by some evil demon, so he concludes that he cannot trust his senses about anything.