“Uncertainty is the refuge of hope.”

“It is not what he has, nor even what he does, which directly expresses the worth of a man, but what he is.”

“all appears to change when we change”

“Conquering any difficulty always gives one a secret joy, for it means pushing back a boundary line and adding to one's liberty.”

“Philosophy means the complete liberty of the mind.”

“I begin to realize that my memory is a great catacomb, and that below my actual standing-ground there is layer after layer of historical ashes. Is the life of mind something like that of great tree...”

“The land of easy mathematics where he who works adds up and he who retires subtracts.”

“At the age of 45, most days in Tucson were spent feeling like I was on the summit of Mauna Kea, as I was exhibiting debilitating health symptoms that corresponded to what I saw at very high altitud...”

“The hour is only long thus, if you've waited.”