"I think, therefore I am — this is the first and most certain conclusion that anyone who philosophizes in order should arrive at."

"The light of natural reason is not less certain than that of revelation."

"To be able to live without fear, without anxiety, without sadness, and without any other passion which could disturb the tranquillity of the soul."

"The light of natural reason is sufficient to give us a clear and distinct conception of God."

"I should know better than to believe that everything I perceive through my senses is true."