Karl Popper Quotes (1902-1994)

“We should realize that from the moral point of view suffering and happiness must not be treated as symmetrical; that is to say, the promotion of happiness is in any case much less urgent than the rendering of help to those who suffer, and the attempt to prevent suffering.”

“It is often asserted that discussion is only possible between people who have a common language and accept common basic assumptions. I think that this is a mistake. All that is needed is a readiness to learn from one's partner in the discussion, which includes a genuine wish to understand what he intends to say. If this readiness is there, the discussion will be the more fruitful the more the partner's backgrounds differ.”

“We must plan for freedom, and not only for security, if for no other reason than only freedom can make security more secure.”

“No matter how many instances of white swans we may have observed, this does not justify the conclusion that all swans are white.”

“The golden rule is a good standard which can perhaps even be improved by doing unto others, wherever possible, as they would be done (unto)...”

“If the matter is presented clearly, it will not be hard to get people to agree that protective institutions are necessary, both on a regional and on a world-wide scale.”

“Next to art, or even equal to it, science – that is, producing and testing theories about the world, about reality – seems to me to be the greatest creative enterprise of which men are capable.”

“The game of science is, in principle, without end. He who decides one day that scientific statements do not call for any further test, and that they can be regarded as finally verified, retires from the game.”

“Through his doctrine of the similarity between Sparta and the perfect state, Plato became one of the most successful propagators of what I should like to call ‘the Great Myth of Sparta’—the perennial and influential myth of the supremacy of the Spartan constitution and way of life.”

“The more we learn about the world, and the deeper our learning, the more conscious, specific, and articulate will be our knowledge of what we do not know, our knowledge of our ignorance. For this, indeed, is the main source of our ignorance — the fact that our knowledge can be only finite, while our ignorance must necessarily be infinite.”

“If we are uncritical we shall always find what we want: we shall look for, and find, confirmations, and we shall look away from, and not see, whatever might be dangerous to our pet theories. In this way it is only too easy to obtain what appears to be overwhelming evidence in favor of a theory which, if approached critically, would have been refuted.”

“Unlimited tolerance must lead to the disappearance of tolerance. If we extend unlimited tolerance even to those who are intolerant, 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. [...] We should therefore claim, in the name of tolerance, the right not to tolerate the intolerant.”

“The history of science, like the history of all human ideas, is a history of irresponsible dreams, of obstinacy, and of error. But science is one of the very few human activities—perhaps the only one — in which errors are systematically criticized and fairly often, in time, corrected. This is why we can say that, in science, we often learn from our mistakes, and why we can speak clearly and sensibly about making progress there.”

“The history of science, like the history of all human ideas, is a history of irresponsible dreams, of obstinacy, and of error. But science is one of the very few human activities — perhaps the only one — in which errors are systematically criticized and fairly often, in time, corrected. This is why we can say that, in science, we often learn from our mistakes, and why we can speak clearly and sensibly about making progress there.”

“Yet the doctrine that man is a machine was argued most forcefully in 1751, long before the theory of evolution became generally accepted, by de La Mettrie; and the theory of evolution gave the problem an even sharper edge, by suggesting there may be no clear distinction between living matter and dead matter. And, in spite of the victory of the new quantum theory and the conversion of so many physicists to indeterminism, de La Mettrie's doctrine that man is a machine has perhaps more defenders than before among physicists, biologists and philosophers; especially in the form of the thesis that man is a computer.”

“This ground-plan, conceived by a great architect, exhibits a fundamental metaphysical dualism in Plato’s thought. ... In politics, it is the opposition between the one collective, the state, which may attain perfection and autarchy, and the great mass of the people—the many individuals, the particular men who must remain imperfect and dependent, and whose particularity is to be suppressed for the sake of the unity of the state (see the next chapter). And this whole dualist philosophy, I believe, originated from the urgent wish to explain the contrast between the vision of an ideal society, and the hateful actual state of affairs in the social field—the contrast between a stable society, and a society in the process of revolution.””

“In my view the ‘normal’ scientist, as Kuhn describes him, is a person one ought to be sorry for. (According to Kuhn’s views about the history of science, many great scientists must have been ‘normal’; yet since I do not feel sorry for them, I do not think that Kuhn’s views can be quite right.) The ‘normal’ scientist, in my view, has been taught badly. I believe, and so do many others, that all teaching on the University level (and if possible below) should be training and encouragement in critical thinking. The ‘normal’ scientist, as described by Kuhn, has been badly taught. He has been taught in a dogmatic spirit: he is a victim of indoctrination. He has learned a technique which can be applied without asking for the reason why (especially in quantum mechanics). As a consequence, he has become what may be called an applied scientist, in contradistinction to what I should call a pure scientist.”

“The Athenian practice had been, even before Plato’s birth, precisely the opposite: the people, the demos, should rule. All important. political decisions—such as war and peace—were made by the assembly of all full citizens. This is now called “direct democracy”; but we must never forget that the citizens formed a minority of the inhabitants—even of the natives. From the point of view here adopted, the important thing is that, in practice, the Athenian democrats regarded their democracy as the alternative to tyranny—to arbitrary rule: in fact, they knew well that a popular leader might be invested with tyrannical powers by a popular vote. So they knew that a popular vote may be wrongheaded, even in the most important matters. (The institution of ostracism recognised this: the ostracised person was banned as a matter of precaution only; he was neither tried nor regarded as guilty.)The Athenians were right: decisions arrived at democratically, and even the powers conveyed upon a government by a democratic vote, may be wrong. It is hard, if not impossible, to construct a constitution that safeguards against mistakes. This is one of the strongest reasons for founding the idea of democracy upon the practical principle of avoiding tyranny rather than upon a divine, or a morally legitimate, right of the people to rule.”

“The so-called paradox of freedom is the argument that freedom in the sense of absence of any constraining control must lead to very great restraint, since it makes the bully free to enslave the meek. The idea is, in a slightly different form, and with very different tendency, clearly expressed in Plato. Less well known is the paradox of tolerance: Unlimited tolerance must lead to the disappearance of tolerance. If we extend unlimited tolerance even to those who are intolerant, 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. — In this formulation, I do not imply, for instance, that we should always suppress the utterance of intolerant philosophies; as long as we can counter them by rational argument and keep them in check by public opinion, suppression would certainly be unwise. But we should claim the right to suppress them if necessary even by force; for it may easily turn out that they are not prepared to meet us on the level of rational argument, but begin by denouncing all argument; they may forbid their followers to listen to rational argument, because it is deceptive, and teach them to answer arguments by the use of their fists or pistols. We should therefore claim, in the name of tolerance, the right not to tolerate the intolerant. We should claim that any movement preaching intolerance places itself outside the law, and we should consider incitement to intolerance and persecution as criminal, in the same way as we should consider incitement to murder, or to kidnapping, or to the revival of the slave trade, as criminal.”

“Characteristics of a scientific theory 1. It is easy to obtain confirmations, or verifications, for nearly every theory — if we look for confirmations. 2. Confirmations should count only if they are the result of risky predictions; that is to say, if, unenlightened by the theory in question, we should have expected an event which was incompatible with the theory—an event which would have refuted the theory. 3. Every "good" scientific theory is a prohibition: it forbids certain things to happen. The more a theory forbids, the better it is. 4. A theory which is not refutable by any conceivable event is non-scientific. Irrefutability is not a virtue of a theory (as people often think) but a vice. 5. Every genuine test of a theory is an attempt to falsify it, or to refute it. Testability is falsifiability; but there are degrees of testability: some theories are more testable, more exposed to refutation, than others; they take, as it were, greater risks. 6. Confirming evidence should not count except when it is the result of a genuine test of the theory; and this means that it can be presented as a serious but unsuccessful attempt to falsify the theory...I now speak in such cases of "corroborating evidence". 7. Some genuinely testable theories, when found to be false, might still be upheld by their admirers—for example by introducing post hoc (after the fact) some auxiliary hypothesis or assumption, or by reinterpreting the theory post hoc in such a way that it escapes refutation. Such a procedure is always possible, but it rescues the theory from refutation only at the price of destroying, or at least lowering, its scientific status, by tampering with evidence. The temptation to tamper can be minimized by first taking the time to write down the testing protocol before embarking on the scientific work.”

“[Bohr was] a marvelous physicist, one of the greatest of all time, but he was a miserable philosopher, and one couldn't talk to him. He was talking all the time, allowing practically only one or two words to you and then at once cutting in.”

“I appeal to the philosophers of all countries to unite and never again mention Heidegger or talk to another philosopher who defends Heidegger. This man was a devil. I mean, he behaved like a devil to his beloved teacher [i.e., Husserl ], and he has a devilish influence on Germany. … One has to read Heidegger in the original to see what a swindler he was.”

“Individualism, united with altruism, has become the basis of our western civilization. It is the central doctrine of Christianity ('love your neighbor,' say the Scriptures, not 'love your tribe'); and it is the core of all ethical doctrines which have grown from our civilization and stimulated it. It is also, for instance, Kant's central practical doctrine ("always recognize that human individuals are ends, and do not use them as mere means to your end.")”

“The Marxist theory of history, in spite of the serious efforts of some of its founders and followers, ultimately adopted this soothsaying practice [of evading testability]. In some of its earlier formulations (for example in Marx's analysis of the character of the 'coming social revolution') their predictions were testable, and in fact falsified. Yet instead of accepting the refutations the followers of Marx re-interpreted both the theory and the evidence in order to make them agree. In this way they rescued the theory from refutation; but they did so at the price of adopting a device which made it irrefutable. They thus gave a 'conventionalist twist' to the theory; and by this stratagem they destroyed its much advertised claim to scientific status.”

“Put in a nut-shell, my thesis amounts to this. The repeated attempts made by Rudolf Carnap to show that the demarcation between science and metaphysics coincides with that between sense and nonsense have failed. The reason is that the positivistic concept of 'meaning' or 'sense' (or of verifiability, or of inductive confirmability, etc.) is inappropriate for achieving this demarcation — simply because metaphysics need not be meaningless even though it is not science. In all its variations demarcation by meaninglessness has tended to be at the same time too narrow and too wide: as against all intentions and all claims, it has tended to exclude scientific theories as meaningless, while failing to exclude even that part of metaphysics which is known as 'rational theology'.”

“Nazism and Fascism are thoroughly beaten, but I must admit that their defeat does not mean that barbarism and brutality have been defeated. On the contrary, it is no use closing our eyes to the fact that these hateful ideas achieved something like a victory in defeat. I have to admit that Hitler succeeded in degrading the moral standards of our Western world, and that in the world of today there is more violence and brutal force than would have been tolerated even in the decade after the first World war. And we must face the possibility that our civilization may ultimately be destroyed by those new weapons which Hitlerism wished upon us, perhaps even within the first decade after the second World war; for no doubt the spirit of Hitlerism won its greatest victory over us when, after its defeat, we used the weapons which the threat of Nazism had induced us to develop.”

“I tried to persuade him to give up his determinism, which amounted to the view that the world was a four-dimensional Parmenidean block universe in which change was a human illusion, or very nearly so. (He agreed that this had been his view, and while discussing it I called him "Parmenides".) I argued that if men, or other organisms, could experience change and genuine succession in time, then this was real. It could not be explained away by a theory of the successive rising into our consciousness of time slices which in some sense coexist; for this kind of "rising into consciousness" would have precisely the same character as that succession of changes which the theory tries to explain away. ... I tried to present to Einstein-Parmenides as strongly as I could my conviction that a clear stand must be made against any idealistic view of time. And I also tried to show that, though the idealistic view was compatible with both determinism and indeterminism, a clear stand should be made in favor of an "open" universe — one in which the future was in no sense contained in the past or the present, even though they do impose severe restrictions on it. I argued that we should not be swayed by our theories to give up realism (for which the strongest arguments were based on common sense), though I think that he was ready to admit, as I was, that we might be forced one day to give it up if very powerful arguments (of Gödel's type, say) were to be brought against it. I therefore argued that with regard to time, and also to indeterminism (that is, the incompleteness of physics), the situation was precisely similar to the situation with regard to realism. Appealing to his own way of expressing things in theological terms, I said: if God had wanted to put everything into the world from the beginning, He would have created a universe without change, without organisms and evolution, and without man and man's experience of change. But He seems to have thought that a live universe with events unexpected even by Himself would be more interesting than a dead one.”

“Socrates (and so Plato) makes it quite clear that the rule of wisdom is tyrannical, and that it cannot tolerate words or deeds, laws or traditional institutions, and certainly political theories that impinge upon its rule. In this sense, modern enemies of Plato's political thought, of whom the most prominent in our time is no doubt Karl Popper, are correct in their objections, although they are ingenuous or let us say insufficiently rigorous in their consideration of the political consequences of theoretical truth. In Popper's case, this is probably due to his conviction that we can establish the falsehood of a proposition but not its truth. This conviction may well be more compatible with democracy in the modern sense of the term than the conviction that genuine philosophers know the truth. The argument of the Republic on the other hand is that, if we did know the truth, we would be led to support a city very much like the one constructed in the Republic under the leadership of Socrates.”

“I do have a great respect for Popper. I mean, I think... he's nearer to... I mean, Popper's ambition, in relation to science, at least, was to discriminate between, sort of, science and what he called pseudo-science.”

“Popper believed that any idea of Utopia is necessarily closed owing to the fact that it chokes its own refutations. The simple notion of a good society that cannot be left open for falsification is totalitarian. I learned from Popper, in addition to the difference between an open and a closed society, that between an open and a closed mind.”

“I read Karl Popper's The Open Society and its Enemies. Popper, whose analysis in many ways complemented that of Hayek, approached Marxism from the point of view of the philosopher of the natural sciences. This meant that he was ideally equipped to expose the fraudulent claim of Marxists to have discovered immutable laws of history, social development or "progress" – laws which were comparable to the laws of natural science. It was not just that the "inevitable" course of events which Marx had prophesied had not occurred and showed no signs of occurring. Marx and Marxists had not even understood the scientific method, let alone practised it in their analysis. Unlike the Marxists – whether historians, economists or social scientists – who tried to "prove" their theories by accumulating more and more facts to sustain them, "the method of science is rather to look out for facts which may refute the theory... and the fact that all tests of the theory are attempted falsifications of predictions derived with its help furnishes the clue to scientific method". The political consequences of this basic error – perhaps more properly described as basic fraud – were summed up by Popper in the dedication of his later book The Poverty of Historicism: "In memory of the countless men, women and children of all creeds or nations or races who fell victims to the fascist and communist belief in Inexorable Laws of Historical Destiny."”

“I got to know Bertrand Russell in the last years of his life. I knew Karl Popper quite well, and they were a whole class above me in intelligence. It wasn’t that I was jealous, it was that I was trying to grapple with these problems with inadequate weaponry… Popper had this originality, Russell had it, and Einstein had it in spades.”