"The greatest minds are capable of the greatest vices as well as of the greatest virtues."

"The senses deceive from time to time, and it is prudent never to trust wholly those who have deceived us even once."

"The two operations of our understanding, intuition and deduction, on which alone we have said we must rely in the acquisition of knowledge."

"It is not enough to apply our mind to things, but we must also apply it to ourselves."

"I concluded that I was a substance whose whole essence or nature consists only in thinking, and that, in order to exist, it needs no place and depends on no material thing."