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Home > Dictionary of Science Quotations > Scientist Names Index P > Karl Raimund Popper Quotes

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Karl Raimund Popper
(28 Jul 1902 - 17 Sep 1994)

Austrian-British philosopher of science remembered for his writings on theory of scientific method.

Science Quotes by Karl Raimund Popper (42 quotes)

>> Click for Karl Raimund Popper Quotes on | Criticism | Falsification | Idea | Knowledge | Refutation | Science | Scientific Method | Test | Theory | Truth |

'Normal' science, in Kuhn's sense, exists. It is the activity of the non-revolutionary, or more precisely, the not-too-critical professional: of the science student who accepts the ruling dogma of the day... in my view the 'normal' scientist, as Kuhn describes him, is a person one ought to be sorry for... He has been taught in a dogmatic spirit: he is a victim of indoctrination... I can only say that I see a very great danger in it and in the possibility of its becoming normal... a danger to science and, indeed, to our civilization. And this shows why I regard Kuhn's emphasis on the existence of this kind of science as so important.
— Karl Raimund Popper
'Normal Science and its Dangers', in I. Lakatos and A. Musgrave (eds.), Criticism and the Growth of Knowledge (1970), 52-3.
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A principle of induction would be a statement with the help of which we could put inductive inferences into a logically acceptable form. In the eyes of the upholders of inductive logic, a principle of induction is of supreme importance for scientific method: “... this principle”, says Reichenbach, “determines the truth of scientific theories. To eliminate it from science would mean nothing less than to deprive science of the power to decide the truth or falsity of its theories. Without it, clearly, science would no longer have the right to distinguish its theories from the fanciful and arbitrary creations of the poet’s mind.” Now this principle of induction cannot be a purely logical truth like a tautology or an analytic statement. Indeed, if there were such a thing as a purely logical principle of induction, there would be no problem of induction; for in this case, all inductive inferences would have to be regarded as purely logical or tautological transformations, just like inferences in inductive logic. Thus the principle of induction must be a synthetic statement; that is, a statement whose negation is not self-contradictory but logically possible. So the question arises why such a principle should be accepted at all, and how we can justify its acceptance on rational grounds.
— Karl Raimund Popper
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A system such as classical mechanics may be ‘scientific’ to any degree you like; but those who uphold it dogmatically — believing, perhaps, that it is their business to defend such a successful system against criticism as long as it is not conclusively disproved — are adopting the very reverse of that critical attitude which in my view is the proper one for the scientist.
— Karl Raimund Popper
In The Logic of Scientific Discovery (1959, reprint 2002), 28.
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Almost everyone... seems to be quite sure that the differences between the methodologies of history and of the natural sciences are vast. For, we are assured, it is well known that in the natural sciences we start from observation and proceed by induction to theory. And is it not obvious that in history we proceed very differently? Yes, I agree that we proceed very differently. But we do so in the natural sciences as well.
In both we start from myths—from traditional prejudices, beset with error—and from these we proceed by criticism: by the critical elimination of errors. In both the role of evidence is, in the main, to correct our mistakes, our prejudices, our tentative theories—that is, to play a part in the critical discussion, in the elimination of error. By correcting our mistakes, we raise new problems. And in order to solve these problems, we invent conjectures, that is, tentative theories, which we submit to critical discussion, directed towards the elimination of error.
— Karl Raimund Popper
The Myth of the Framework: In Defence of Science and Rationality (1993), 140.
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But I shall certainly admit a system as empirical or scientific only if it is capable of being tested by experience. These considerations suggest that not the verifiability but the falsifiability of a system is to be taken as a criterion of demarcation. In other words: I shall not require of a scientific system that it shall be capable of being singled out, once and for all, in a positive sense; but I shall require that its logical form shall be such that it can be singled out, by means of empirical tests, in a negative sense: it must be possible for an empirical scientific system to be refuted by experience. (1959)
— Karl Raimund Popper
The Logic of Scientific Discovery: Logik Der Forschung (1959, 2002), 18.
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I am opposed to looking upon logic as a kind of game. … One might think that it is a matter of choice or convention which logic one adopts. I disagree with this view.
— Karl Raimund Popper
Objective Knowledge: an Evolutionary Approach (1972), 304.
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I think that we shall have to get accustomed to the idea that we must not look upon science as a 'body of knowledge,' but rather as a system of hypotheses; that is to say, as a system of guesses or anticipations which in principle cannot be justified, but with which we work as long as they stand up to tests, and of which we are never justified in saying that we know they are 'true' or 'more or less certain' or even 'probable.'
— Karl Raimund Popper
The Logic of Scientific Discovery (1959), 317.
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In my view, aiming at simplicity and lucidity is a moral duty of all intellectuals: lack of clarity is a sin, and pretentiousness is a crime.
— Karl Raimund Popper
Objective Knowledge: an Evolutionary Approach (1972), 44
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In point of fact, no conclusive disproof of a theory can ever be produced; for it is always possible to say that the experimental results are not reliable or that the discrepancies which are asserted to exist between the experimental results and the theory are only apparent and that they will disappear with the advance of our understanding. If you insist on strict proof (or strict disproof) in the empirical sciences, you will never benefit from experience, and never learn from it how wrong you are.
— Karl Raimund Popper
The Logic of Scientific Discovery: Logik Der Forschung (1959, 2002), 28.
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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 Raimund Popper
The Logic of Scientific Discovery (2002), 316.
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It is a myth that the success of science in our time is mainly due to the huge amounts of money that have been spent on big machines. What really makes science grow is new ideas, including false ideas.
— Karl Raimund Popper
As quoted by Adam Gopnik, writing about his meeting with Popper at home, in 'The Porcupine: A Pilgrimage to Popper' in The New Yorker (1 Apr 2002).
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It is easy to obtain confirmations, or verifications, for nearly every theory—if we look for confirmations. Confirmations should count only if they are the result of risky predictions... 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. Every genuine test of a theory is an attempt to falsify it, or refute it.
— Karl Raimund Popper
Conjectures and Refutations: The Growth of Scientific Knowledge (1963), 36.
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It is his intuition, his mystical insight into the nature of things, rather than his reasoning which makes a great scientist.
— Karl Raimund Popper
In The Open Society and Its Enemies (1945).

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 Raimund Popper
In The Logic of Scientific Discovery (1959, 1972), 281.
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It is the rule which says that the other rules of scientific procedure must be designed in such a way that they do not protect any statement in science against falsification. (1959)
— Karl Raimund Popper
The Logic of Scientific Discovery: Logik Der Forschung (2002), 33.
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Man, some modern philosophers tell us, is alienated from his world: he is a stranger and afraid in a world he never made. Perhaps he is; yet so are animals, and even plants. They too were born, long ago, into a physico-chemical world, a world they never made.
— Karl Raimund Popper
'A Realist View of Logic Physics', in Wolfgang Yourgrau, et al., Physics, Logic, and History: based on the First International Colloquium held at the University of Denver, May 16-20, 1966 (1970), 1.
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My thesis is that what we call 'science' is differentiated from the older myths not by being something distinct from a myth, but by being accompanied by a second-order tradition—that of critically discussing the myth. … In a certain sense, science is myth-making just as religion is.
— Karl Raimund Popper
Conjectures and Refutations: the Growth of Scientific Knowledge (2002), 170-171.
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My view of the matter, for what it is worth, is that there is no such thing as a logical method of having new ideas, or a logical reconstruction of this process. My view may be expressed by saying that every discovery contains an “irrational element,” or “a creative intuition,” in Bergson's sense. In a similar way Einstein speaks of the “search for those highly universal laws … from which a picture of the world can be obtained by pure deduction. There is no logical path.” he says, “leading to these … laws. They can only be reached by intuition, based upon something like an intellectual love (Einfühlung) of the objects of experience.”
— Karl Raimund Popper
In The Logic of Scientific Discovery: Logik Der Forschung (1959, 2002), 8.
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Our knowledge can only be finite, while our ignorance must necessarily be infinite.
— Karl Raimund Popper
Essy, 'On the Sources of Knowledge and of Ignorance', in Conjectures and Refutations: The Growth of Scientific Knowledge (1962), 28.
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Piecemeal social engineering resembles physical engineering in regarding the ends as beyond the province of technology. (All that technology may say about ends is whether or not they are compatible with each other or realizable.)
— Karl Raimund Popper
In The Poverty of Historicism (1960), 64.
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Propose theories which can be criticized. Think about possible decisive falsifying experiments—crucial experiments. But do not give up your theories too easily—not, at any rate, before you have critically examined your criticism.
— Karl Raimund Popper
'The Problem of Demarcation' (1974). Collected in David Miller (ed.) Popper Selections (1985), 126-127.
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Psychologism is, I believe, correct only in so far as it insists upon what may be called “methodological individualism” as opposed to “methodological collectivism”; it rightly insists that the “behaviour” and the “actions” of collectives, such as states or social groups, must be reduced to the behaviour and to the actions of human individuals. But the belief that the choice of such an individualist method implies the choice of a psychological method is mistaken.
— Karl Raimund Popper
In The Open Society and Its Enemies (1945), Vol. 22, 87.
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Science is not a system of certain, or -established, statements; nor is it a system which steadily advances towards a state of finality... And our guesses are guided by the unscientific, the metaphysical (though biologically explicable) faith in laws, in regularities which we can uncover—discover. Like Bacon, we might describe our own contemporary science—'the method of reasoning which men now ordinarily apply to nature'—as consisting of 'anticipations, rash and premature' and as 'prejudices'.
— Karl Raimund Popper
The Logic of Scientific Discovery (1959), 278.
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Some scientists find, or so it seems, that they get their best ideas when smoking; others by drinking coffee or whisky. Thus there is no reason why I should not admit that some may get their ideas by observing, or by repeating observations.
— Karl Raimund Popper
Realism and the Aim of Science (1983), 36.
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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 Raimund Popper
In Objective Knowledge: An Evolutionary Approach (1972), 70. As cited in Alexander Naraniecki, Returning to Karl Popper: A Reassessment of his Politics and Philosophy (2014), 89, footnote.
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The difficulties connected with my criterion of demarcation (D) are important, but must not be exaggerated. It is vague, since it is a methodological rule, and since the demarcation between science and nonscience is vague. But it is more than sharp enough to make a distinction between many physical theories on the one hand, and metaphysical theories, such as psychoanalysis, or Marxism (in its present form), on the other. This is, of course, one of my main theses; and nobody who has not understood it can be said to have understood my theory.
The situation with Marxism is, incidentally, very different from that with psychoanalysis. Marxism was once a scientific theory: it predicted that capitalism would lead to increasing misery and, through a more or less mild revolution, to socialism; it predicted that this would happen first in the technically highest developed countries; and it predicted that the technical evolution of the 'means of production' would lead to social, political, and ideological developments, rather than the other way round.
But the (so-called) socialist revolution came first in one of the technically backward countries. And instead of the means of production producing a new ideology, it was Lenin's and Stalin's ideology that Russia must push forward with its industrialization ('Socialism is dictatorship of the proletariat plus electrification') which promoted the new development of the means of production.
Thus one might say that Marxism was once a science, but one which was refuted by some of the facts which happened to clash with its predictions (I have here mentioned just a few of these facts).
However, Marxism is no longer a science; for it broke the methodological rule that we must accept falsification, and it immunized itself against the most blatant refutations of its predictions. Ever since then, it can be described only as nonscience—as a metaphysical dream, if you like, married to a cruel reality.
Psychoanalysis is a very different case. It is an interesting psychological metaphysics (and no doubt there is some truth in it, as there is so often in metaphysical ideas), but it never was a science. There may be lots of people who are Freudian or Adlerian cases: Freud himself was clearly a Freudian case, and Adler an Adlerian case. But what prevents their theories from being scientific in the sense here described is, very simply, that they do not exclude any physically possible human behaviour. Whatever anybody may do is, in principle, explicable in Freudian or Adlerian terms. (Adler's break with Freud was more Adlerian than Freudian, but Freud never looked on it as a refutation of his theory.)
The point is very clear. Neither Freud nor Adler excludes any particular person's acting in any particular way, whatever the outward circumstances. Whether a man sacrificed his life to rescue a drowning, child (a case of sublimation) or whether he murdered the child by drowning him (a case of repression) could not possibly be predicted or excluded by Freud's theory; the theory was compatible with everything that could happen—even without any special immunization treatment.
Thus while Marxism became non-scientific by its adoption of an immunizing strategy, psychoanalysis was immune to start with, and remained so. In contrast, most physical theories are pretty free of immunizing tactics and highly falsifiable to start with. As a rule, they exclude an infinity of conceivable possibilities.
— Karl Raimund Popper
'The Problem of Demarcation' (1974). Collected in David Miller (ed.) Popper Selections (1985), 127-128.
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The empirical basis of objective science has nothing “absolute” about it. Science does not rest upon solid bedrock. The bold structure of its theories rises, as it were, above a swamp. It is like a building erected on piles. The piles are driven down from above into the swamp, but not down to any natural or “given” base; and when we cease our attempts to drive our piles into a deeper layer, it is not because we have reached firm ground. We simply stop when we are satisfied that they are firm enough to carry the structure, at least for the time being.
— Karl Raimund Popper
The Logic of Scientific Discovery: Logik Der Forschung (1959, 2002), 94.
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The growth of our knowledge is the result of a process closely resembling what Darwin called “natural selection”; that is, the natural selection of hypotheses: our knowledge consists, at every moment, of those hypotheses which have shown their (comparative) fitness by surviving so far in their struggle for existence, a competitive struggle which eliminates those hypotheses which are unfit.
— Karl Raimund Popper
From Objective Knowledge: An Evolutionary Approach (1971), 261. As quoted in Dean Keith Simonton, Origins of Genius: Darwinian Perspectives on Creativity (1999), 26.
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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. In most other fields of human endeavour there is change, but rarely progress ... And in most fields we do not even know how to evaluate change.
— Karl Raimund Popper
From Conjectures and Refutations: The Growth of Scientific Knowledge (1963), 216. Reproduced in Karl Popper, Truth, Rationality and the Growth of Scientific Knowledge (1979), 9.
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The influence (for good or ill) of Plato's work is immeasurable. Western thought, one might say, has been Platonic or anti-Platonic, but hardly ever non-Platonic.
— Karl Raimund Popper
The Open Society and its Enemies (1945).
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The initial stage, the act of conceiving or inventing a theory, seems to me neither to call for logical analysis nor to be susceptible of it. (1959)
— Karl Raimund Popper
In The Logic of Scientific Discovery: Logik Der Forschung (1959, 2002), 7.
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The metaphysical doctrine of determinism simply asserts that all events in this world are fixed, or unalterable, or predetermined. It does not assert that they are known to anybody, or predictable by scientific means. But it asserts that the future is as little changeable as is the past. Everybody knows what we mean when we say that the past cannot be changed. It is in precisely the same sense that the future cannot be changed, according to metaphysical determinism.
— Karl Raimund Popper
Karl Raimund Popper and William Warren Bartley (ed.), The Open Universe: an Argument for Indeterminism (1991), 8.
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The method of science depends on our attempts to describe the world with simple theories: theories that are complex may become untestable, even if they happen to be true. Science may be described as the art of systematic over-simplification—the art of discerning what we may with advantage omit.
— Karl Raimund Popper
Karl Raimund Popper and William Warren Bartley (ed.), The Open Universe: an Argument for Indeterminism (1991), 44. by Karl Raimund Popper, William Warren Bartley - Science - 1991
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The old scientific ideal of episteme — of absolutely certain, demonstrable knowledge — has proved to be an idol. The demand for scientific objectivity makes it inevitable that every scientific statement must remain tentative for ever. (1959)
— Karl Raimund Popper
The Logic of Scientific Discovery: Logik Der Forschung (1959, 2002), 280.
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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.
— Karl Raimund Popper
Conjectures and Refutations: the Growth of Scientific Knowledge (2002), 66.
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Theories are nets cast to catch what we call “the world”: to rationalize, to explain, and to master it. We endeavor to make the mesh ever finer and finer.
— Karl Raimund Popper
In The Logic of Scientific Discovery (1959).

There can be no ultimate statements science: there can be no statements in science which can not be tested, and therefore none which cannot in principle be refuted, by falsifying some of the conclusions which can be deduced from them.
— Karl Raimund Popper
The Logic of Scientific Discovery (1959), 47.
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Thus science must begin with myths, and with the criticism of myths; neither with the collection of observations, nor with the invention of experiments, but with the critical discussion of myths, and of magical techniques and practices.
— Karl Raimund Popper
In Conjectures and Refutations: the Growth of Scientific Knowledge (1963, 2002), 66.
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To give a causal explanation of an event means to deduce a statement which describes it, using as premises of the deduction one or more universal laws, together with certain singular statements, the initial conditions ... We have thus two different kinds of statement, both of which are necessary ingredients of a complete causal explanation. (1959)
— Karl Raimund Popper
The Logic of Scientific Discovery: Logik Der Forschung (1959, 2002), 38.
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Understanding a theory has, indeed, much in common with understanding a human personality. We may know or understand a man's system of dispositions pretty well; that is to say, we may be able to predict how he would act in a number of different situations. But since there are infinitely many possible situations, of infinite variety, a full understanding of a man's dispositions does not seem to be possible.
— Karl Raimund Popper
Objective Knowledge: an Evolutionary Approach (1972), 299.
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[Great scientists] are men of bold ideas, but highly critical of their own ideas: they try to find whether their ideas are right by trying first to find whether they are not perhaps wrong. They work with bold conjectures and severe attempts at refuting their own conjectures.
— Karl Raimund Popper
'The Problem of Demarcation' (1974). Collected in David Miller (ed.) Popper Selections (1985), 118-119.
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[The aim of science is] to explain what so far has taken to be an explicans, such as a law of nature. The task of empirical science constantly renews itself. We may go on forever, proceeding to explanations of a higher and higher universality…
— Karl Raimund Popper
"The Aim of Science', Ratio 1 (1958), 26. Quoted in Erhard Scheibe and Brigitte Falkenburg (ed), Between Rationalism and Empiricism: Selected Papers in the Philosophy of Physics (2001), 238
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Quotes by others about Karl Raimund Popper (5)

To turn Karl [Popper]'s view on its head, it is precisely the abandonment of critical discourse that marks the transition of science. Once a field has made the transition, critical discourse recurs only at moments of crisis when the bases of the field are again in jeopardy. Only when they must choose between competing theories do scientists behave like philosophers.
'Logic of Discovery or Psychology of Research', in I. Lakatos and A. Musgrave (eds.), Criticism and the Growth of Knowledge (1970), 6-7.
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With time, I attempt to develop hypotheses that are more risky. I agree with [Karl] Popper that scientists need to be interested in risky hypotheses because risky hypotheses advance science by producing interesting thoughts and potential falsifications of theories (of course, personally, we always strive for verification—we love our theories after all; but we should be ready to falsify them as well.
'Grand Theories and Mid-Range Theories&3039;, essay in Ken G. Smith (ed.) and Michael A. Hitt (ed), Great Minds in Management: the Theory of Process Development (2005), 89.
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Part of the appeal was that Medawar was not only a Nobel Laureate, but he seemed like a Nobel Laureate; he was everything one thought a Nobel Laureate ought to be. If you have ever wondered why scientists like Popper, try Medawar's exposition. Actually most Popperian scientists have probably never tried reading anything but Medawar's exposition.
'The Art of the Developable', New York Review of Books (Oct 1983). The first two sentences, slightly edited, were reprinted in A Devil's Chaplain (2004), 196.
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When we seek a textbook case for the proper operation of science, the correction of certain error offers far more promise than the establishment of probable truth. Confirmed hunches, of course, are more upbeat than discredited hypotheses. Since the worst traditions of ‘popular’ writing falsely equate instruction with sweetness and light, our promotional literature abounds with insipid tales in the heroic mode, although tough stories of disappointment and loss give deeper insight into a methodology that the celebrated philosopher Karl Popper once labeled as ‘conjecture and refutation.’
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Belief may be a regrettably unavoidable biological weakness to be kept under the control of criticism: but commitment is for Popper an outright crime.
In 'Falsification and the Methodology of Scientific Research Programmes', in I. Lakatos and A. Musgrave (eds.), Criticism and the Growth of Knowledge: Proceedings of the International Colloquium in the Philosophy of Science, London 1965 (1970), Vol. 4, 92.
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See also:
  • 28 Jul - short biography, births, deaths and events on date of Popper's birth.

Carl Sagan Thumbnail In science it often happens that scientists say, 'You know that's a really good argument; my position is mistaken,' and then they would actually change their minds and you never hear that old view from them again. They really do it. It doesn't happen as often as it should, because scientists are human and change is sometimes painful. But it happens every day. I cannot recall the last time something like that happened in politics or religion. (1987) -- Carl Sagan
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