I say quite deliberately that the Christian religion, as organized in its churches, has been and still is the principal enemy of moral progress in the world.
Love can flourish only as long as it is free and spontaneous; it tends to be killed by the thought of duty. To say that it is your duty to love so-and-so is the surest way to cause you to hate him of her.
Three passions, simple but overwhelmingly strong, have governed my life: the longing for love, the search for knowledge, and unbearable pity for the suffering of mankind.
There is no reason to suppose that the world had a beginning at all. The idea that things must have a beginning is really due to the poverty of our thoughts.
The secret of happiness is very simple: let your interests be as wide as possible, and let your reactions to the things and persons that interest you be as far as possible friendly rather than hostile.
The wise man thinks about his troubles only when there is some purpose in doing so; at other times he thinks about other things, or, if it is night, about nothing at all.
