"The human mind is seldom satisfied, and is certainly never exercising its highest functions, when it is doing the work of a calculating machine."

"Thoroughly conscious ignorance is the prelude to every real advance in science."

"If I am not mistaken, there is a good deal of nonsense in the world."

"I have been thinking about the nature of things, and I have come to the conclusion that there is a good deal of it."

"The only use of a knowledge of the past is to equip us for the present."