“The mind once enlightened cannot again become dark.”

“Ignorance is of a peculiar nature; once dispelled, it is impossible to reestablish it. It is not originally a thing of itself, but is only the absence of knowledge; and though man may be kept ignorant, he cannot be made ignorant.”

“To believe that God created a plurality of worlds, at least as numerous as what we call stars, renders the Christian faith at once little and ridiculous; and scatters it in the mind like feathers in the air.”

“An army of principles can penetrate where an army of soldiers cannot.”

“Man cannot make principles, he can only discover them.”

“My own mind is my own church.”

“We have it in our power to begin the world over again.”