It is impossible to speak in such a way that you cannot be misunderstood.

All we can do is search for the falsity content in our best theory.

The defence of democracy must consist in making anti-democratic experiences too costly for those who try them; much more costly than a democratic compromise

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.

Every genuine test of a theory is an attempt to falsify it, or to refute it.

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.

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.