"The sceptic says “nothing can be known”; he is a dogmatist, though a negative one. His creed, we must admit, is paralyzing, and a nation which accepts it is doomed to defeat, since it cannot adduce adequate motives for self-defence. But the scientific attitude is quite different. It does not say “knowledge is impossible,” but “knowledge is difficult.” As against the dogmatist, it holds that nothing can count as knowledge unless it has been submitted to the tests that science has shown to be useful, and even then, it may require correction in the light of fresh evidence. As against the sceptic, it holds that what has emerged from a scientific scrutiny is more likely to be true than what has not, and that in many cases this likelihood is almost certainty; in any event, it is the best hypothesis to accept in practice. The dogmatist accepts one hypothesis regardless of the evidence; the sceptic rejects all hypotheses regardless of the evidence. Both are irrational. The rational man accepts the most probable hypothesis for the time being, while continuing to look for new evidence to confirm or confute it."
- Bertrand Russell, Scepticism and Tolerance, 1948