All scientific knowledge to which man owes his role as master of the world arose from playful activities.

Hatred of humanity and love of animals make a very bad combination.

The human soul is very much older than the human mind.

The neuro-physiological organization which we call instinct functions in a blindly mechanical way, particularly apparent when its function goes wrong.

Every man gets a narrower and narrower field of knowledge in which he must be an expert in order to compete with other people. The specialist knows more and more about less and less and finally knows everything about nothing.

All the advantages that man has gained from his ever-deepening understanding of the natural world that surrounds him, his technological, chemical and medical progress, all of which should seem to alleviate human suffering... tends instead to favor humanity's destruction.

More than any other product of human scientific culture scientific knowledge is the collective property of all mankind.