A smile happens in a flash, but its memory can last a lifetime.

Calculus required continuity, and continuity was supposed to require the infinitely little; but nobody could discover what the infinitely little might be.

Philosophy, though unable to tell us with certainty what is the true answer to the doubts which it raises, is able to suggest many possiblities which enlarge our thoughts and free them from the tyranny of custom. Thus, while diminishing our feeling of certainty as to what things are, it greatly increases our knowledge as to what the may be; it removes the somewhat arrogant dogmatism of those who have never travelled into the region of liberating doubt, and it keeps alive our sense of wonder by showing familar things in an unfamilar aspect

Morality in sexual relations, when it is free from superstition, consists essentially in respect for the other person, and unwillingness to use that person solely as a means of personal gratification, without regard to his or her desires.

Be isolated, be ignored, be attacked, be in doubt, be frightened, but do not be silenced.

The dictum that human nature cannot be changed is one of those tiresome platitudes that conceal from the ignorant the depths of their own ignorance.

Patriotism which has the quality of intoxication is a danger not only to its native land but to the world, and "My country never wrong" is an even more dangerous maxim than "My country, right or wrong."