Every solution of a problem raises new unsolved problems.

The scientific tradition is distinguished from the pre-scientific tradition by having two layers. Like the latter, it passes on its theories; but it also passes on a critical attitude towards them.

Why do I think that we, the intellectuals, are able to help? Simply because we, the intellectuals, have done the most terrible harm for thousands of years. Mass murder in the name of an idea, a doctrine, a theory, a religion - that is all "our" doing, "our" invention: the invention of the intellectuals. If only we would stop setting man against man - often with the best intentions - much would be gained. Nobody can say that it is impossible for us to stop doing this.

Ignorance is not a simple lack of knowledge but an active aversion to knowledge, the refusal to know, issuing from cowardice, pride, or laziness of mind.

A theory is just a mathematical model to describe the observations.

A rationalist is simply someone for whom it is more important to learn than to be proved right; someone who is willing to learn from others - not by simply taking over another's opinions, but by gladly allowing others to criticize his ideas and by gladly criticizing the ideas of others

Optimism is a duty. The future is open. It is not predetermined. No one can predict it, except by chance. We all contribute to determining it by what we do. We are all equally responsible for its success.