We are quite rich enough to defend ourselves, whatever the cost. We must now learn that we are quite rich enough to educate ourselves as we need to be educated.

Men are mortal, but ideas are immortal.

The radical novelty of modern science lies precisely in the rejection of the belief... that the forces which move the stars and atoms are contingent upon the preferences of the human heart.

A man cannot sleep in his cradle: whatever is useful must in the nature of life become useless.

When men are brought face to face with their opponents, forced to listen and learn and mend their ideas, they cease to be children and savages and begin to live like civilized men. Then only is freedom a reality, when men may voice their opinions because they must examine their opinions.

Many a time I have wanted to stop talking and find out what I really believed.

When everyone thinks alike, no one thinks very much.