He that has eyes to see and ears to hear may convince himself that no mortal can keep a secret. If his lips are silent, he chatters with his fingertips; betrayal oozes out of him at every pore.

To be completely honest with oneself is the very best effort a human being can make.

Neither in my private life nor in my writings, have I ever made a secret of being an out-and-out unbeliever.

It is impossible to overlook the extent to which civilization is built upon a renunciation of instinct.

Conscience is the internal perception of the rejection of a particular wish operating within us.

Adolescent stage in the development of the human race from which humanity should free itself.

It is a mistake to believe that science consists in nothing but conclusively proved propositions, and it is unjust to demand that it should. It is a demand made by those who feel a craving for authority in some form to replace the religious catechism by something else, even a scientific one.