"I am a thinking substance, that is, a mind, or soul, or intellect, or reason."

"I think, therefore I am a doubt."

"I always wanted to learn to distinguish the true from the false, in order to see clearly in my actions and to walk with confidence in this life."

"I have always held that the two questions, God and the Soul, were the chief of those which ought to be demonstrated by the help of philosophy rather than of theology."

"I know that I exist, but I do not know what I am."