"We must say that there are as many squares as there are numbers."

"We cannot teach people anything; we can only help them discover it within themselves."

"If I were again beginning my studies, I would follow the advice of Plato and start with mathematics."

"I think that in the discussion of natural problems we ought to begin not with the Scriptures, but with experiments, and demonstrations."

"I've loved the stars too fondly to be fearful of the night."

"Measure what is measurable, and make measurable what is not so."

"Where the senses fail us, reason must step in."

"It is surely harmful to souls to make it a heresy to believe what is proved."

"I do not feel obliged to believe that the same God who has endowed us with sense, reason, and intellect has intended us to forgo their use."

"The Bible shows the way to go to heaven, not the way the heavens go."

"It vexes me when they would constrain science by the authority of the Scriptures, and yet do not consider themselves bound to answer reason and experiment."

"By denying scientific principles, one may maintain any paradox."

"The sun, with all those planets revolving around it and dependent on it, can still ripen a bunch of grapes as if it had nothing else in the universe to do."

"The Milky Way is nothing else but a mass of innumerable stars planted together in clusters."

"Nature is relentless and unchangeable, and it is indifferent as to whether its hidden reasons and actions are understandable to man or not."

"I have never met a man so ignorant that I couldn't learn something from him."

"Facts which at first seem improbable will, even on scant explanation, drop the cloak which has hidden them and stand forth in naked and simple beauty."

"In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual."