"Perfect numbers like perfect men are very rare."

"I have never made any distinction between the sciences, but have always held that all are linked together, and that it is easier to learn them all at once than to learn one separately."

"I have long ago observed that in order to study the truth, it is necessary once in the course of our life to demolish everything completely and start again from the foundations."

"The first precept was never to accept a thing as true until I knew it as such without a single doubt."

"I am accustomed to take my sleep for granted, and I often imagine that I dream of the most important things, when after all I am only dreaming."