"No rational argument will have a rational effect on a man who does not want to adopt a rational attitude."

"Whenever a theory appears to you as the only possible one, take this as a sign that you have neither understood the theory nor the problem which it was intended to solve."

"We have become makers of our fate when we have ceased to pose as its prophets."

"Science may be described as the art of systematic over-simplification."

"Our knowledge can only be finite, while our ignorance must necessarily be infinite."

"We must plan for freedom, and not only for security, if for no other reason than that only freedom can make security secure."

"In so far as a scientific statement speaks about reality, it must be falsifiable; and in so far as it is not falsifiable, it does not speak about reality."

"Science must begin with myths, and with the criticism of myths."

"There is no history of mankind, there are only many histories of all kinds of aspects of human life. And one of these is the history of political power. This is elevated into the history of the world."

"Piecemeal social engineering resembles physical engineering in regarding the ends as beyond the province of technology."

"Those who promise us paradise on earth never produced anything but a hell."

"Good tests kill flawed theories; we remain alive to guess again."