In Descartes' First Meditation, why does he set about doubting all of his knowledge? What is he hoping to achieve? Descartes mentions that several years have passed since he first realized how numerous were the false opinions that he had once taken to be true. He notes that the subsequent opinions he built were suspect to doubt because of this. He says that he has gained his knowledge through senses or through the senses. The senses are sometimes deceptive, and it is prudent not to trust that which