It is complete nihilism to propose laying down arms in a world where atom bombs are around. It is very simple: there is no way of achieving peace other than with weapons.

The moral decisions of others should be treated with respect, as long as such decisions do not conflict with the principle of tolerance.

Science is the century-old endeavour to bring together by means of systematic thought the perceptible phenomena of this world into as thorough-going an association as possible. To put it boldly, it is the attempt at a posterior reconstruction of existence by the process of conceptualization. Science can only ascertain what is, but not what should be, and outside of its domain value judgements of all kinds remain necessary.

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

It is not his possession of knowledge, of irrefutable truth, that makes the man of science, but his persistent and recklessly critical quest for truth.

No number of sightings of white swans can prove the theory that all swans are white. The sighting of just one black one may disprove it.

You cannot have a rational discussion with a man who prefers shooting you to being convinced by you.