Top 140 Karl Popper Quotes (2025 Update)

1. “All life is problem solving.”

— Karl Popper

Featured in: Problem-Solving Quotes

2. “True ignorance is not the absence of knowledge, but the refusal to acquire it.”

— Karl Popper

3. “I may be wrong and you may be right, and by an effort, we may get nearer to the truth.”

— Karl Popper

Featured in: Doubt Quotes

4. “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.”

— Karl Popper

Featured in: Make A Difference Quotes

5. “It is part of my thesis that all our knowledge grows only through the correcting of our mistakes.”

— Karl Popper

6. “A theory that explains everything, explains nothing.”

— Karl Popper

7. “Those who promise us paradise on earth never produced anything but a hell.”

— Karl Popper

8. “If you can’t say it simply and clearly, keep quiet, and keep working on it till you can.”

— Karl Popper

9. “The attempt to make heaven on earth invariably produces hell.”

— Karl Popper

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

— Karl Popper

11. “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.”

— Karl Popper

12. “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.”

— Karl Popper

13. “Every solution of a problem raises new unsolved problems.”

— Karl Popper

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

— Karl Popper

15. “We do not know. We can only guess.”

— Karl Popper

16. “The only way to test a hypothesis is to look for all the information that disagrees with it.”

— Karl Popper

17. “The growth of knowledge depends entirely upon disagreement.”

— Karl Popper

18. “Science must begin with myths, and with the criticism of myths.”

— Karl Popper

19. “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.”

— Karl Popper

20. “It can’t happen here is always wrong: a dictatorship can happen anywhere.”

— Karl Popper

21. “The survival value of intelligence is that it allows us to extinct a bad idea, before the idea extincts us.”

— Karl Popper

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

— Karl Popper

23. “There is no history, only histories.”

— Karl Popper

24. “We should therefore claim, in the name of tolerance, the right not to tolerate the intolerant.”

— Karl Popper

25. “Our knowledge can only be finite, while our ignorance must necessarily be infinite.”

— Karl Popper

26. “The best thing that can happen to a human being us to find a problem, to fall in love with that problem, and to live trying to solve that problem, unless another problem even more lovable appears.”

— Karl Popper

27. “The difference between the amoeba and Einstein is that, although both make use of the method of trial and error elimination, the amoeba dislikes erring while Einstein is intrigued by it.”

— Karl Popper

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

— Karl Popper

29. “The history of science is everywhere speculative. It is a marvelous hiatory. It makes you proud to be a human being.”

— Karl Popper

30. “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.”

— Karl Popper

31. “There will be well-testable theories, hardly testable theories, and non-testable theories. Those which are non-testable are of no interest to empirical scientists. They may be described as metaphysical.”

— Karl Popper

32. “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.”

— Karl Popper

33. “I have spoken to Einstein and he admitted to me that his theory was in fact no different from the one of Parmenides.”

— Karl Popper

34. “All things living are in search of a better world .”

— Karl Popper

35. “Evolution is not a fact. Evolution doesn’t even qualify as a theory or as a hypothesis. It is a metaphysical research program, and it is not really testable science.”

— Karl Popper

36. “While differing widely in the various little bits we know, in our infinite ignorance we are all equal.”

— Karl Popper

37. “If we are not prepared to defend a tolerant society against the onslaught of the intolerant, then the tolerant will be destroyed, and tolerance with them.”

— Karl Popper

38. “What really makes science grow is new ideas, including false ideas.”

— Karl Popper

39. “If you know that things are bound to happen whatever you do, then you may feel free to give up the fight against them.”

— Karl Popper

40. “Good tests kill flawed theories; we remain alive to guess again.”

— Karl Popper

41. “No book can ever be finished. While working on it we learn just enough to find it immature the moment we turn away from it.”

— Karl Popper

42. “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.”

— Karl Popper

43. “The quest for precision is analogous to the quest for certainty and both – precision and certainty are impossible to attain.”

— Karl Popper

44. “It is wrong to think that belief in freedom always leads to victory; we must always be prepared for it to lead to defeat. If we choose freedom, then we must be prepared to perish along with it.”

— Karl Popper

45. “We all remember how many religious wars were fought for a religion of love and gentleness; how many bodies were burned alive with the genuinely kind intention of saving souls from the eternal fire of hell.”

— Karl Popper

46. “The genuine rationalist does not think that he or anyone else is in possession of the truth; nor does he think that mere criticism as such helps us achieve new ideas. But he does think that, in the sphere of ideas, only critical discussion can help us sort the wheat from the chaff.”

— Karl Popper

47. “Simple statements are to be prized more highly than less simple ones because they tell us more; because their empirical content is greater; and because they are better testable.”

— Karl Popper

48. “It is wrong to ask who will rule. The ability to vote a bad government out of office is enough. That is democracy.”

— Karl Popper

49. “Serious rational criticism is so rare that it should be encouraged. Being too ready to defend oneself is more dangerous than being too ready to admit a mistake.”

— Karl Popper

50. “Science is perhaps the only human activity in which errors are systematically criticized and, in time, corrected.”

— Karl Popper