Karl Popper

Karl Popper CH FRS FBA
Born	28 July 1902 Vienna, Austria
Died	17 September 1994(1994-09-17) (aged 92) London, England
Era	20th century philosophy
Region	Western philosophy
School	Analytic Critical rationalism Fallibilism Evolutionary epistemology Liberalism
Main interests	Epistemology Philosophy of science Social and political philosophy Philosophy of mind
Notable ideas	Falsifiability Hypothetico-deductive method Open society

Sir Karl Raimund Popper, CH, FRS, FBA (28 July 1902 – 17 September 1994) was an Austro-British philosopher and a professor at the London School of Economics. He is regarded as one of the greatest philosophers of science of the 20th century; he also wrote extensively on social and political philosophy.

Popper is known for his attempt to repudiate the classical observationalist / inductivist account of scientific method by advancing empirical falsification instead; for his opposition to the classical justificationist account of knowledge which he replaced with critical rationalism, "the first non justificational philosophy of criticism in the history of philosophy"; and for his vigorous defense of liberal democracy and the principles of social criticism that he came to believe made a flourishing "open society" possible.

Life

Karl Popper was born in Vienna (then in Austria-Hungary) in 1902, to upper middle-class parents of assimilated Jewish origins, both of whom had converted to Christianity. Karl's father Simon Siegmund Carl Popper was a lawyer from Bohemia, and mother Jenny Schiff was of Silesian and Hungarian descent. After establishing themselves in Vienna, the Poppers made a rapid social climb in Viennese society: Simon Siegmund Carl became a legal partner of Vienna's liberal mayor Raimond Grübl and, after his death in 1898, took over the firm (Karl received his middle name from the mayor).

Popper received a Lutheran upbringing and was educated at the University of Vienna. His father was a doctor of law at the Vienna University and a bibliophile who had 12,000–14,000 volumes in his personal library. Popper inherited from him both the library and the disposition.

In 1919, Popper became attracted by Marxism and subsequently joined the Association of Socialist School Students. He also became a member of the Social Democratic Workers' Party of Austria, which was at that time a party that fully adopted the Marxist ideology. He soon became disillusioned by what he saw to be the philosophical restraints imposed by the historical materialism of Marx, abandoned the ideology and remained a supporter of social liberalism throughout his life.

In 1928, he earned a doctorate in Philosophy and then, from 1930 to 1936, taught secondary school. Popper published his first book, Logik der Forschung (The Logic of Scientific Discovery), in 1934. Here, he criticised psychologism, naturalism, inductionism, and logical positivism, and put forth his theory of potential falsifiability as the criterion demarcating science from non-science.

Gravesite on the Wiener Küniglberg

In 1937, the rise of Nazism and the threat of the Anschluss led Popper to emigrate to New Zealand, where he became lecturer in philosophy at Canterbury University College New Zealand (at Christchurch). In 1946, he moved to England to become reader in logic and scientific method at the London School of Economics. Three years later, he was appointed as professor of logic and scientific method at the University of London in 1949. Popper was president of the Aristotelian Society from 1958 to 1959. He was knighted by Queen Elizabeth II in 1965, and was elected a Fellow of the Royal Society in 1976. He retired from academic life in 1969, though he remained intellectually active for the rest of his life. He was invested with the Insignia of a Companion of Honour in 1982. Popper was a member of the Academy of Humanism and described himself as an agnostic, showing respect for the moral teachings of Judaism and Christianity.

Popper won many awards and honours in his field, including the Lippincott Award of the American Political Science Association, the Sonning Prize, and fellowships in the Royal Society, British Academy, London School of Economics, King's College London, Darwin College Cambridge, and Charles University, Prague. Austria awarded him the Grand Decoration for Services to the Republic of Austria in Gold.

Popper died in Croydon, UK at the age of 92 on 17 September 1994. After cremation, his ashes were taken to Vienna and buried at Lainzer cemetery adjacent to the ORF Centre, where his wife Josefine Anna Henninger, who had died in Austria several years before, had already been buried.

Popper's philosophy

Philosophy of science

Popper coined the term critical rationalism to describe his philosophy. The term indicates his rejection of classical empiricism, and of the classical observationalist-inductivist account of science that had grown out of it. Popper argued strongly against the latter, holding that scientific theories are abstract in nature, and can be tested only indirectly, by reference to their implications. He also held that scientific theory, and human knowledge generally, is irreducibly conjectural or hypothetical, and is generated by the creative imagination in order to solve problems that have arisen in specific historio-cultural settings. Logically, no number of positive outcomes at the level of experimental testing can confirm a scientific theory, but a single counterexample is logically decisive: it shows the theory, from which the implication is derived, to be false. The term "falsifiable" does not mean something is false; rather, that if it is false, then this can be shown by observation or experiment. Popper's account of the logical asymmetry between verification and falsifiability lies at the heart of his philosophy of science. It also inspired him to take falsifiability as his criterion of demarcation between what is and is not genuinely scientific: a theory should be considered scientific if and only if it is falsifiable. This led him to attack the claims of both psychoanalysis and contemporary Marxism to scientific status, on the basis that their theories are not falsifiable. Popper also wrote extensively against the famous Copenhagen interpretation of quantum mechanics. He strongly disagreed with Niels Bohr's instrumentalism and supported Albert Einstein's realist approach to scientific theories about the universe. Popper's falsifiability resembles Charles Peirce's nineteenth century fallibilism. In Of Clocks and Clouds (1966), Popper remarked that he wished he had known of Peirce's work earlier.

In All Life is Problem Solving, Popper sought to explain the apparent progress of scientific knowledge—how it is that our understanding of the universe seems to improve over time. This problem arises from his position that the truth content of our theories, even the best of them, cannot be verified by scientific testing, but can only be falsified. Again, in this context the word 'falsified' does not refer to something being 'fake'; rather, that something can be (i.e., is capable of being) shown to be false by observation or experiment. Some things simply do not lend themselves to being shown to be false, and therefore are not falsifiable. If so, then how is it that the growth of science appears to result in a growth in knowledge? In Popper's view, the advance of scientific knowledge is an evolutionary process characterized by his formula:

$PS_{1}\rightarrow TT_{1}\rightarrow EE_{1}\rightarrow PS_{2}.\,$

In response to a given problem situation ($PS_{1}$), a number of competing conjectures, or tentative theories ($TT$), are systematically subjected to the most rigorous attempts at falsification possible. This process, error elimination ($EE$), performs a similar function for science that natural selection performs for biological evolution. Theories that better survive the process of refutation are not more true, but rather, more "fit"—in other words, more applicable to the problem situation at hand ($PS_{1}$). Consequently, just as a species' biological fitness does not ensure continued survival, neither does rigorous testing protect a scientific theory from refutation in the future. Yet, as it appears that the engine of biological evolution has produced, over time, adaptive traits equipped to deal with more and more complex problems of survival, likewise, the evolution of theories through the scientific method may, in Popper's view, reflect a certain type of progress: toward more and more interesting problems ($PS_{2}$). For Popper, it is in the interplay between the tentative theories (conjectures) and error elimination (refutation) that scientific knowledge advances toward greater and greater problems; in a process very much akin to the interplay between genetic variation and natural selection.

Where does "truth" fit into all this? As early as 1934 Popper wrote of the search for truth as "one of the strongest motives for scientific discovery." Still, he describes in Objective Knowledge (1972) early concerns about the much-criticized notion of truth as correspondence. Then came the semantic theory of truth formulated by the logician Alfred Tarski and published in 1933. Popper writes of learning in 1935 of the consequences of Tarski's theory, to his intense joy. The theory met critical objections to truth as correspondence and thereby rehabilitated it. The theory also seemed, in Popper's eyes, to support metaphysical realism and the regulative idea of a search for truth.

According to this theory, the conditions for the truth of a sentence as well as the sentences themselves are part of a metalanguage. So, for example, the sentence "Snow is white" is true if and only if snow is white. Although many philosophers have interpreted, and continue to interpret, Tarski's theory as a deflationary theory, Popper refers to it as a theory in which "is true" is replaced with "corresponds to the facts". He bases this interpretation on the fact that examples such as the one described above refer to two things: assertions and the facts to which they refer. He identifies Tarski's formulation of the truth conditions of sentences as the introduction of a "metalinguistic predicate" and distinguishes the following cases:

1. "John called" is true.
2. "It is true that John called."

The first case belongs to the metalanguage whereas the second is more likely to belong to the object language. Hence, "it is true that" possesses the logical status of a redundancy. "Is true", on the other hand, is a predicate necessary for making general observations such as "John was telling the truth about Phillip."

Upon this basis, along with that of the logical content of assertions (where logical content is inversely proportional to probability), Popper went on to develop his important notion of verisimilitude or "truthlikeness".

The intuitive idea behind verisimilitude is that the assertions or hypotheses of scientific theories can be objectively measured with respect to the amount of truth and falsity that they imply. And, in this way, one theory can be evaluated as more or less true than another on a quantitative basis which, Popper emphasizes forcefully, has nothing to do with "subjective probabilities" or other merely "epistemic" considerations.

The simplest mathematical formulation that Popper gives of this concept can be found in the tenth chapter of Conjectures and Refutations. Here he defines it as:

$Vs(a)=CT_{v}(a)-CT_{f}(a)\,$

where $Vs(a)$ is the verisimilitude of a, $CT_{v}(a)$ is a measure of the content of truth of a, and $CT_{f}(a)$ is a measure of the content of the falsity of a.

Knowledge, for Popper, was objective, both in the sense that it is objectively true (or truthlike), and also in the sense that knowledge has an ontological status (i.e., knowledge as object) independent of the knowing subject (Objective Knowledge: An Evolutionary Approach, 1972). He proposed three worlds (see Popperian cosmology): World One, being the physical world, or physical states; World Two, being the world of mind, or mental states, ideas, and perceptions; and World Three, being the body of human knowledge expressed in its manifold forms, or the products of the second world made manifest in the materials of the first world (i.e.–books, papers, paintings, symphonies, and all the products of the human mind). World Three, he argued, was the product of individual human beings in exactly the same sense that an animal path is the product of individual animals, and that, as such, has an existence and evolution independent of any individual knowing subjects. The influence of World Three, in his view, on the individual human mind (World Two) is at least as strong as the influence of World One. In other words, the knowledge held by a given individual mind owes at least as much to the total accumulated wealth of human knowledge, made manifest, as to the world of direct experience. As such, the growth of human knowledge could be said to be a function of the independent evolution of World Three. Many contemporary philosophers have not embraced Popper's Three World conjecture, due mostly, it seems, to its resemblance to Cartesian dualism.

Political philosophy

In The Open Society and Its Enemies and The Poverty of Historicism, Popper developed a critique of historicism and a defence of the 'Open Society'. Popper considered historicism to be the theory that history develops inexorably and necessarily according to knowable general laws towards a determinate end. He argued that this view is the principal theoretical presupposition underpinning most forms of authoritarianism and totalitarianism. He argued that historicism is founded upon mistaken assumptions regarding the nature of scientific law and prediction. Since the growth of human knowledge is a causal factor in the evolution of human history, and since "no society can predict, scientifically, its own future states of knowledge", it follows, he argued, that there can be no predictive science of human history. For Popper, metaphysical and historical indeterminism go hand in hand. In After The Open Society, which was published posthumously, a large collection of his previously unpublished and uncollected essays on social and political topics was assembled. In this, one can trace his ideas from material that pre-dated The Open Society and Its Enemies to something that was completed just as he died.

In a 1992 lecture, Popper explained the connection between his political philosophy and his philosophy of science. As he stated, he was in his early years impressed by communism and also active in the Austrian Communist party. What had a profound effect on him was an event that happened in 1918: during a riot, caused by the Communists, the police shot several people, including some of Popper's friends. When Popper later told the leaders of the Communist party about this, they responded by stating that this loss of life was necessary in working towards the inevitable workers' revolution. This statement did not convince Popper and he started to think about what kind of reasoning would justify such a statement. He later concluded that there could not be any justification for it, and this was the start of his later criticism of historicism.

In 1947, Popper founded with Friedrich Hayek, Milton Friedman, Ludwig von Mises and others the Mont Pelerin Society to defend classical liberalism, in the spirit of the Open Society.

The paradox of tolerance

Although Popper was an advocate of toleration, he opined that even a tolerant person cannot always accept another's intolerance.

For, if tolerance allowed intolerance to succeed completely, tolerance itself would be threatened. In The Open Society and Its Enemies: The Spell of Plato, he argued that:

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.

The utterance of intolerant philosophies should not always be suppressed, "as long as we can counter them by rational argument and keep them in check by public opinion." However,

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.

Furthermore, in support of human rights legislation in the second half of the 20th century, he stated:

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.

Problem of induction

Among his contributions to philosophy is his attempt to answer the philosophical problem of induction as emphasized strongly by David Hume. The problem, in basic terms, can be understood by example: given that the sun has risen every day for as long as anyone can remember, what is the rational proof that it will rise tomorrow? How can one rationally prove that past events will continue to repeat in the future, just because they have repeated in the past?

Popper claims to have found a solution to the problem of induction. His reply is characteristic, and ties in with his criterion of falsifiability. He states that while there is no way to prove that the sun will rise, it is possible to formulate the theory that every day the sun will rise—if it does not rise on some particular day, the theory will be falsified and will have to be replaced by a different one. Until that day, there is no need to reject the assumption that the theory is true. Neither is it rational according to Popper to instead make the more complex assumption that the sun will rise until a given day, but will stop doing so the day after, or similar statements with additional conditions.

Such a theory would be true with higher probability, because it cannot be attacked so easily: To falsify the first one, it is sufficient to find that sun has stopped rising; to falsify the second one, one additionally needs the assumption that the given day has not yet been reached. Popper held that it is the least likely, or most easily falsifiable, or simplest theory (attributes which he all identified as the same thing) that explains known facts that one should rationally prefer. His opposition to positivism, which held that it is the theory most likely to be true that one should prefer, here becomes very apparent. It is impossible, Popper argues, to ensure a theory to be true (but not fatal, since even false theories may have true consequence); it is more important that they can be eliminated and corrected as easily as possible if false.

Popper and Hume agreed that there is often a psychological belief that the sun will rise tomorrow, but both denied that there is logical justification for the supposition that it will, simply because it always has in the past. Popper writes:

"I approached the problem of induction through Hume. Hume, I felt, was perfectly right in pointing out that induction cannot be logically justified." (Conjectures and Refutations, p. 55)

To Popper, who was an anti-justificationist, traditional philosophy is misled by the false principle of sufficient reason. He thinks that no assumption can ever be or needs ever to be justified, so a lack of justification is not a justification for doubt. Instead, theories should be tested and scrutinized. It is not the goal to bless theories with claims of certainty or justification, but to eliminate errors in them:

"there are no such things as good positive reasons; nor do we need such things [...] But [philosophers] obviously cannot quite bring [themselves] to believe that this is my opinion, let alone that it is right" (The Philosophy of Karl Popper, p. 1043)

Free will

Popper and John Eccles speculated on the problem of free will for many years generally agreeing on an interactionist dualist theory of mind. However, although Popper was a body-mind dualist, he did not think that the mind is a substance separate from the body: he thought that mental or psychological properties or aspects of people are distinct from physical ones.

When he gave the first Arthur Holly Compton Memorial Lecture in 1955, Popper revisited the idea of quantum indeterminacy as a source of human freedom. Eccles had suggested that "critically poised neurons" might be influenced by the mind to assist in a decision. Popper criticized Compton's idea of amplified quantum events affecting the decision. He wrote

"The idea that the only alternative to determinism is just sheer chance was taken over by Schlick, together with many of his views on the subject, from Hume, who asserted that 'the removal' of what he called 'physical necessity' must always result in

'the same thing with chance. As objects must either be conjoin'd or not, . . . 'tis impossible to admit of any medium betwixt chance and an absolute necessity'.

"I shall later argue against this important doctrine according to which the alternative to determinism is sheer chance. Yet I must admit that the doctrine seems to hold good for the quantum-theoretical models which have been designed to explain, or at least to illustrate, the possibility of human freedom. This seems to be the reason why these models are so very unsatisfactory.

"Hume's and Schlick's ontological thesis that there cannot exist anything intermediate between chance and determinism seems to me not only highly dogmatic (not to say doctrinaire) but clearly absurd; and it is understandable only on the assumption that they believed in a complete determinism in which chance has no status except as a symptom of our ignorance."

Popper called not for something between chance and necessity but for a combination of randomness and control to explain freedom, though not yet explicitly in two stages with random chance before the controlled decision.

"freedom is not just chance but, rather, the result of a subtle interplay between something almost random or haphazard, and something like a restrictive or selective control."

Then in his 1977 book with John Eccles, The Self and its Brain, Popper finally formulates the two-stage model in a temporal sequence. And he compares free will to Darwinian evolution and natural selection,

"New ideas have a striking similarity to genetic mutations. Now, let us look for a moment at genetic mutations. Mutations are, it seems, brought about by quantum theoretical indeterminacy (including radiation effects). Accordingly, they are also probabilistic and not in themselves originally selected or adequate, but on them there subsequently operates natural selection which eliminates inappropriate mutations. Now we could conceive of a similar process with respect to new ideas and to free-will decisions, and similar things.

"That is to say, a range of possibilities is brought about by a probabilistic and quantum mechanically characterized set of proposals, as it were - of possibilities brought forward by the brain. On these there then operates a kind of selective procedure which eliminates those proposals and those possibilities which are not acceptable to the mind."

Other thinkers who have formulated a two-stage model for free will include William James, Henri Poincaré, Arthur Compton, Henry Margenau, and Daniel Dennett.

Issue of Darwinism

Karl Popper famously stated "Darwinism is not a testable scientific theory, but a metaphysical research program." He continued:

And yet, the theory is invaluable. I do not see how, without it, our knowledge could have grown as it has done since Darwin. In trying to explain experiments with bacteria which become adapted to, say, penicillin, it is quite clear that we are greatly helped by the theory of natural selection. Although it is metaphysical, it sheds much light upon very concrete and very practical researches. It allows us to study adaptation to a new environment (such as a penicillin-infested environment) in a rational way: it suggests the existence of a mechanism of adaptation, and it allows us even to study in detail the mechanism at work.

He also noted that theism presented as explaining adaptation "was worse than an open admission of failure, for it created the impression that an ultimate explanation had been reached."

He later said

When speaking here of Darwinism, I shall speak always of today's theory - that is Darwin's own theory of natural selection supported by the Mendelian theory of heredity, by the theory of the mutation and recombination of genes in a gene pool, and by the decoded genetic code. This is an immensely impressive and powerful theory. The claim that it completely explains evolution is of course a bold claim, and very far from being established. All scientific theories are conjectures, even those that have successfully passed many severe and varied tests. The Mendelian underpinning of modern Darwinism has been well tested, and so has the theory of evolution which says that all terrestrial life has evolved from a few primitive unicellular organisms, possibly even from one single organism.

He explained that the difficulty of testing had led some people to describe natural selection as a tautology, and that he too had in the past described the theory as 'almost tautological', and had tried to explain how the theory could be untestable (as is a tautology) and yet of great scientific interest. His

solution was that the doctrine of natural selection is a most successful metaphysical research programme. It raises detailed problems in many fields, and it tells us what we would expect of an acceptable solution of these problems. I still believe that natural selection works in this way as a research programme. Nevertheless, I have changed my mind about the testability and logical status of the theory of natural selection; and I am glad to have an opportunity to make a recantation.

Popper summarized his new view as follows:

The theory of natural selection may be so formulated that it is far from tautological. In this case it is not only testable, but it turns out to be not strictly universally true. There seem to be exceptions, as with so many biological theories; and considering the random character of the variations on which natural selection operates, the occurrence of exceptions is not surprising. Thus not all phenomena of evolution are explained by natural selection alone. Yet in every particular case it is a challenging research program to show how far natural selection can possibly be held responsible for the evolution of a particular organ or behavioral program.

Influence

Karl Popper in 1990.

Popper played a vital role in establishing the philosophy of science as a vigorous, autonomous discipline within analytic philosophy, through his own prolific and influential works, and also through his influence on his own contemporaries and students. Popper founded in 1946 the Department of Philosophy, Logic and Scientific Method at the London School of Economics and there lectured and influenced both Imre Lakatos and Paul Feyerabend, two of the foremost philosophers of science in the next generation of philosophy of science. (Lakatos significantly modified Popper's position, and Feyerabend repudiated it entirely, but the work of both is deeply influenced by Popper and engaged with many of the problems that Popper set.)

While there is some dispute as to the matter of influence, Popper had a long-standing and close friendship with economist Friedrich Hayek, who was also brought to the London School of Economics from Vienna. Each found support and similarities in each other's work, citing each other often, though not without qualification. In a letter to Hayek in 1944, Popper stated, "I think I have learnt more from you than from any other living thinker, except perhaps Alfred Tarski." Popper dedicated his Conjectures and Refutations to Hayek. For his part, Hayek dedicated a collection of papers, Studies in Philosophy, Politics, and Economics, to Popper, and in 1982 said, "...ever since his Logik der Forschung first came out in 1934, I have been a complete adherent to his general theory of methodology."

Popper also had long and mutually influential friendships with art historian Ernst Gombrich, biologist Peter Medawar, and neuro-scientist John Carew Eccles.

Popper's influence, both through his work in philosophy of science and through his political philosophy, has also extended beyond the academy. Among Popper's students and advocates at the London School of Economics is the billionaire investor George Soros, who says his investment strategies are modelled on Popper's understanding of the advancement of knowledge through the distinctly Hegelian idea of falsification. Among Soros's philanthropic foundations is the Open Society Institute, a think-tank named in honour of Popper's The Open Society and Its Enemies, which Soros founded to advance the Popperian defense of the open society against authoritarianism and totalitarianism.

Popperian philosophy also inspired the creation of Taking Children Seriously, a libertarian movement which noticed that Popper's general theory of knowledge creation does not differentiate between adults and children.

Criticism

Criticism of his philosophy of science

Most criticisms of Popper's philosophy are of the falsification, or error elimination, element in his account of problem solving. In interpreting these, it is important to bear in mind the aims of his idea. It is intended as an ideal, practical method of effective human problem solving; as such, the current conclusions of science are stronger than pseudo-sciences or non-sciences, insofar as they have survived this particularly vigorous selection method. He does not argue that any such conclusions are therefore true, or that this describes the actual methods of any particular scientist.

Rather, it is a recommended ideal method that, if enacted by a system or community, will over time lead to slow but steady progress of a sort (relative to how well the system or community enacts the method). It has been suggested that Popper's ideas are often mistaken for a hard logical account of truth because of the historical co-incidence of their appearing at the same time as logical positivism, the followers of which mistook his aims for their own.

The Quine-Duhem thesis argues that it's impossible to test a single hypothesis on its own, since each one comes as part of an environment of theories. Thus we can only say that the whole package of relevant theories has been collectively falsified, but cannot conclusively say which element of the package must be replaced. An example of this is given by the discovery of the planet Neptune: when the motion of Uranus was found not to match the predictions of Newton's laws, the theory "There are seven planets in the solar system" was rejected, and not Newton's laws themselves. Popper discussed this critique of naïve falsificationism in Chapters 3 & 4 of The Logic of Scientific Discovery. For Popper, theories are accepted or rejected via a sort of selection process. Theories that say more about the way things appear are to be preferred over those that do not; the more generally applicable a theory is, the greater its value. Thus Newton’s laws, with their wide general application, are to be preferred over the much more specific “the solar system has seven planets”.

Thomas Kuhn’s influential book The Structure of Scientific Revolutions argued that scientists work in a series of paradigms, and that falsificationist methodologies would make science impossible.

"No theory ever solves all the puzzles with which it is confronted at a given time; nor are the solutions already achieved often perfect. On the contrary, it is just the incompleteness and imperfection of the existing data-theory fit that, at any given time, define many of the puzzles that characterize normal science. If any and every failure to fit were ground for theory rejection, all theories ought to be rejected at all times. On the other hand, if only severe failure to fit justifies theory rejection, then the Popperians will require some criterion of 'improbability' or of 'degree of falsification.' In developing one they will almost certainly encounter the same network of difficulties that has haunted the advocates of the various probabilistic verification theories [that the evaluative theory cannot itself be legitimated without appeal to another evaluative theory, leading to regress]"---The Structure of Scientific Revolutions. pp. 145-6.

Popper's student Imre Lakatos attempted to reconcile Kuhn’s work with falsificationism by arguing that science progresses by the falsification of research programs rather than the more specific universal statements of naïve falsificationism. Another of Popper’s students Paul Feyerabend ultimately rejected any prescriptive methodology, and argued that the only universal method characterizing scientific progress was anything goes.

Popper claimed to have recognized already in the 1934 version of his Logic of Discovery a fact later stressed by Kuhn, "that scientists necessarily develop their ideas within a definite theoretical framework", and to that extent to have anticipated Kuhn's central point about 'normal science'. (But Popper criticised what he saw as Kuhn's relativism.) Also, in his collection Conjectures and Refutations: The Growth of Scientific Knowledge (Harper & Row, 1963), Popper writes, "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. The scientific tradition is distinguished from the pre-scientific tradition in having two layers. Like the latter, it passes on its theories; but it also passes on a critical attitude towards them. The theories are passed on, not as dogmas, but rather with the challenge to discuss them and improve upon them."

Another objection is that it is not always possible to demonstrate falsehood definitively, especially if one is using statistical criteria to evaluate a null hypothesis. More generally it is not always clear, if evidence contradicts a hypothesis, that this is a sign of flaws in the hypothesis rather than of flaws in the evidence. However, this is a misunderstanding of what Popper's philosophy of science sets out to do. Rather than offering a set of instructions that merely need to be followed diligently to achieve science, Popper makes it clear in The Logic of Scientific Discovery that his belief is that the resolution of conflicts between hypotheses and observations can only be a matter of the collective judgment of scientists, in each individual case.

Popper's falsificationism can be questioned logically: it is not clear how Popper would deal with a statement like "for every metal, there is a temperature at which it will melt." The hypothesis cannot be falsified by any possible observation, for there will always be a higher temperature than tested at which the metal may in fact melt, yet it seems to be a valid scientific hypothesis. These examples were pointed out by Carl Gustav Hempel. Hempel came to acknowledge that Logical Positivism's verificationism was untenable, but argued that falsificationism was equally untenable on logical grounds alone. The simplest response to this is that, because Popper describes how theories attain, maintain and lose scientific status, individual consequences of currently accepted scientific theories are scientific in the sense of being part of tentative scientific knowledge, and both of Hempel's examples fall under this category. For instance, atomic theory implies that all metals melt at some temperature.

An early adversary of so-called critical rationalism, Karl-Otto Apel attempted a comprehensive refutation of Popper's philosophy. In Transformation der Philosophie (1973), Apel charged Popper with being guilty of, amongst other things, a pragmatic contradiction.

Other criticism

It has been argued that Popper's student Imre Lakatos transformed Popper's philosophy using historicism and updated Hegelian historiographic ideas.

Ludwig Wittgenstein was accused of brandishing a poker at Popper during a meeting of the Cambridge Moral Sciences Club, when they argued about whether issues in philosophy were real or just linguistic puzzles. Wittgenstein's friends say he was merely handling a poker, but Popper used the situation to make a joke at Wittgenstein's expense.

Charles Taylor accuses Popper of exploiting his worldwide fame as an epistemologist to diminish the importance of philosophers of the 20th century continental tradition. According to Taylor, Popper's criticisms are completely baseless, but they are received with an attention and respect that Popper's "intrinsic worth hardly merits". William W. Bartley defended Popper against such allegations: "Sir Karl Popper is not really a participant in the contemporary professional philosophical dialogue; quite the contrary, he has ruined that dialogue. If he is on the right track, then the majority of professional philosophers the world over has wasted or is wasting their intellectual careers. The gulf between Popper's way of doing philosophy and that of the bulk of professional philosophers is as great as that between astronomy and astrology."

In 2004, philosopher and psychologist Michel ter Hark (Groningen, The Netherlands) published a book, called Popper, Otto Selz and the rise of evolutionary epistemology, ISBN 0-521-83074-5, in which he claimed that Popper took some of his ideas from his tutor, the German psychologist Otto Selz. Selz himself never published his ideas, partly because of the rise of Nazism which forced him to quit his work in 1933, and the prohibition of referring to Selz' work. Popper, the historian of ideas and his scholarship, is criticized in some academic quarters, for his rejection of Plato, Hegel and Marx.

According to Karl Popper, a theory is scientific only in so far as it is falsifiable, and should be given up as soon as it is falsified. By applying Popper's account of scientific method, John Gray's Straw Dogs states that this would have killed the theories of Darwin and Einstein at birth. When they were first advanced, each of them was at odds with some available evidence; only later did evidence become available that gave them crucial support.

See also

• Calculus of predispositions
• Contributions to liberal theory
• Evolutionary epistemology
• Liberalism
• Liberalism in Austria
• Popper's experiment (quantum mechanics)
• Popperian cosmology
• Predispositioning Theory

Bibliography

• The Two Fundamental Problems of the Theory of Knowledge, 1930–33 (as a typescript circulating as Die beiden Grundprobleme der Erkenntnistheorie; as a German book 1979, as English translation 2008), ISBN 0-415-39431-7
• The Logic of Scientific Discovery, 1934 (as Logik der Forschung, English translation 1959), ISBN 0-415-27844-9
• The Poverty of Historicism, 1936 (private reading at a meeting in Brussels, 1944/45 as a series of journal articles in Econometrica, 1957 a book), ISBN 0-415-06569-0
• The Open Society and Its Enemies, 1945 Vol 1 ISBN 0-415-29063-5, Vol 2 ISBN 0-415-29063-5
• Quantum Theory and the Schism in Physics, 1956/57 (as privately circulated galley proofs; published as a book 1982), ISBN 0-415-09112-8
• The Open Universe: An Argument for Indeterminism, 1956/57 (as privately circulated galley proofs; published as a book 1982), ISBN 0-415-07865-2
• Realism and the Aim of Science, 1956/57 (as privately circulated galley proofs; published as a book 1983), ISBN 0-09-151450-9
• Conjectures and Refutations: The Growth of Scientific Knowledge, 1963, ISBN 0-415-04318-2
• Objective Knowledge: An Evolutionary Approach, 1972, Rev. ed., 1979, ISBN 0-19-875024-2
• Unended Quest; An Intellectual Autobiography, 1976, ISBN 0-415-28590-9
• The Self and Its Brain: An Argument for Interactionism (with Sir John C. Eccles), 1977, ISBN 0-415-05898-8
• In Search of a Better World, 1984, ISBN 0-415-13548-6
• Die Zukunft ist offen (The Future is Open) (with Konrad Lorenz), 1985 (in German), ISBN 3-492-00640-X
• A World of Propensities, 1990, ISBN 1-85506-000-0
• The Lesson of this Century, (Interviewer: Giancarlo Bosetti, English translation: Patrick Camiller), 1992, ISBN 0-415-12958-3
• All life is Problem Solving, 1994, ISBN 0-415-24992-9
• The Myth of the Framework: In Defence of Science and Rationality, (Edited by Mark Amadeus Notturno) 1994, ISBN 0-415-13555-9
• Knowledge and the Mind-Body Problem: In Defence of Interaction, (Edited by Mark Amadeus Notturno) 1994 ISBN 0-415-11504-3
• The World of Parmenides, Essays on the Presocratic Enlightenment, 1998, (Edited by Arne F. Petersen with the assistance of Jørgen Mejer), ISBN 0-415-17301-9
• After The Open Society, 2008. (Edited by Jeremy Shearmur and Piers Norris Turner, this volume contains a large number of Popper's previously unpublished or uncollected writings on political and social themes.) ISBN 978-0-415-30908-0
• Frühe Schriften, 2006 (Edited by Troels Eggers Hansen, includes Popper's writings and publications from before the Logic, including his previously unpublished thesis, dissertation and journal articles published that relate to the Wiener Schulreform) ISBN 978-3-16-147632-7

Further reading

• [Comprehensive bibliography:] Lube, Manfred: Karl R. Popper. Bibliographie 1925–2004. Wissenschaftstheorie, Sozialphilosophie, Logik, Wahrscheinlichkeitstheorie, Naturwissenschaften. Frankfurt/Main etc.: Peter Lang, 2005. 576 pp. (Schriftenreihe der Karl Popper Foundation Klagenfurt.3.)- Current edition: http://ub.uni-klu.ac.at/cms/sondersammlungen/karl-popper-sammlung/bibliographie/
• Stefano Gattei. Karl Popper's Philosophy of Science. 2009.
• David Miller. Critical Rationalism: A Restatement and Defence. 1994.
• David Miller (Ed.). Popper Selections.
• John W. N. Watkins. Science and Skepticism. 1984.
• Bailey, Richard, Education in the Open Society: Karl Popper and Schooling. Aldershot, UK: Ashgate 2000. The only book-length examination of Popper's relevance to education.
• Bartley, William Warren III. Unfathomed Knowledge, Unmeasured Wealth. La Salle, IL: Open Court Press 1990. A look at Popper and his influence by one of his students.
• Berkson, William K., and Wettersten, John. Learning from Error: Karl Popper's Psychology of Learning. La Salle, IL: Open Court 1984
• Edmonds, D., Eidinow, J. Wittgenstein's Poker. New York: Ecco 2001. A review of the origin of the conflict between Popper and Ludwig Wittgenstein, focused on events leading up to their volatile first encounter at 1946 Cambridge meeting.
• Feyerabend, Paul Against Method. London: New Left Books, 1975. A polemical, iconoclastic book by a former colleague of Popper's. Vigorously critical of Popper's rationalist view of science.
• Hacohen, M. Karl Popper: The Formative Years, 1902–1945. Cambridge: Cambridge University Press, 2000.
• Hickey, J. Thomas. History of the Twentieth-Century Philosophy of Science Book V, Karl Popper And Falsificationist Criticism. www.philsci.com . 1995* Kadvany, John Imre Lakatos and the Guises of Reason. Durham and London: Duke University Press, 2001. ISBN 0-8223-2659-0. Explains how Imre Lakatos developed Popper's philosophy into a historicist and critical theory of scientific method.
• Keuth, Herbert. The Philosophy of Karl Popper. Cambridge: Cambridge University Press, 2004. An accurate scholarly overview of Popper's philosophy, ideal for students.
• Kuhn, Thomas S. The Structure of Scientific Revolutions. Chicago: University of Chicago Press, 1962. Central to contemporary philosophy of science is the debate between the followers of Kuhn and Popper on the nature of scientific enquiry. This is the book in which Kuhn's views received their classical statement.
• Lakatos, I & Musgrave, A (eds.) (1970), Criticism and the Growth of Knowledge, Cambridge (Cambridge University Press). ISBN 0-521-07826-1
• Levinson, Paul, ed. In Pursuit of Truth: Essays on the Philosophy of Karl Popper on the Occasion of his 80th Birthday. Atlantic Highlands, NJ: Humanities Press, 1982. A collection of essays on Popper's thought and legacy by a wide range of his followers. Includes an interview with Sir Ernst Gombrich.
• Lindh, Allan Goddard (11 November 1993). "Did Popper solve Hume's problem?". Nature. 366 (6451): 105–106. doi:10.1038/366105a0.
• Magee, Bryan. Popper. London: Fontana, 1977. An elegant introductory text. Very readable, albeit rather uncritical of its subject, by a former Member of Parliament.
• Magee, Bryan. Confessions of a Philosopher, Weidenfeld and Nicolson, 1997. Magee's philosophical autobiography, with a chapter on his relations with Popper. More critical of Popper than in the previous reference.
• Munz, Peter. Beyond Wittgenstein's Poker: New Light on Popper and Wittgenstein Aldershot, Hampshire, UK: Ashgate, 2004. ISBN 0-7546-4016-7. Written by the only living student of both Wittgenstein and Popper, an eyewitness to the famous "poker" incident described above (Edmunds & Eidinow). Attempts to synthesize and reconcile the differences between these two philosophers.
• Niemann, Hans-Joachim. Lexikon des Kritischen Rationalismus, (Encyclopaedia of Critical Raionalism), Tübingen (Mohr Siebeck) 2004, ISBN 3-16-148395-2. More than a thousand headwords about critical rationalism, the most important arguments of K.R. Popper and H. Albert, quotations of the original wording. Edition for students in 2006, ISBN 3-16-149158-0.
• Notturno, Mark Amadeus. "Objectivity, Rationality, and the Third Realm: Justification and the Grounds of Psychologism". Boston: Martinus Nijhoff, 1985.
• Notturno, Mark Amadeus. On Popper. Wadsworth Philosophers Series. 2003. A very comprehensive book on Popper’s philosophy by an accomplished Popperian.
• Notturno, Mark Amadeus. "Science and the Open Society". New York: CEU Press, 2000.
• O'Hear, Anthony. Karl Popper. London: Routledge, 1980. A critical account of Popper's thought, viewed from the perspective of contemporary analytic philosophy.
• Radnitzky, Gerard, Bartley, W. W., III eds. Evolutionary Epistemology, Rationality, and the Sociology of Knowledge. La Salle, IL: Open Court Press 1987. ISBN 0-8126-9039-7. A strong collection of essays by Popper, Campbell, Munz, Flew, et al., on Popper's epistemology and critical rationalism. Includes a particularly vigorous answer to Rorty's criticisms.
• Richmond, Sheldon. Aesthetic Criteria: Gombrich and the Philosophies of Science of Popper and Polanyi. Rodopi, Amsterdam/Atlanta, 1994, 152 pp. ISBN 90-5183-618-X.
• Rowbottom, Darrell P. Popper's Critical Rationalism: A Philosophical Investigation. London: Routledge, 2010. A research monograph on Popper's philosophy of science and epistemology. It critiques and develops critical rationalism in light of more recent advances in mainstream philosophy.
• Schilpp, Paul A., ed. The Philosophy of Karl Popper, 2 vols. La Salle, IL: Open Court Press, 1974. One of the better contributions to the Library of Living Philosophers series. Contains Popper's intellectual autobiography, a comprehensive range of critical essays, and Popper's responses to them. ISBN 0-87548-141-8 (vol.I). ISBN 0-87548-142-6 (Vol II)
• Schroeder-Heister, P. "Popper, Karl Raimund (1902–94)," International Encyclopedia of the Social & Behavioral Sciences, 2001, pp. 11727–11733.Abstract.
• Shearmur, Jeremy. The Political Thought of Karl Popper. London and New York: Routledge, 1996. Study of Popper's political thought by a former assistant of Popper's. Makes use of archive sources and studies the development of Popper's political thought and its inter-connections with his epistemology.
• Stokes, G. Popper: Philosophy, Politics and Scientific Method. Cambridge: Polity Press, 1998. A very comprehensive, balanced study, which focuses largely on the social and political side of Popper's thought.
• Stove, D.C., Popper and After: Four Modern Irrationalists. Oxford: Pergamon. 1982. A vigorous attack, especially on Popper's restricting himself to deductive logic.
• Thornton, Stephen. "Karl Popper," Stanford Encyclopedia of Philosophy, 2006.
• Weimer, W., Palermo, D., eds. Cognition and the Symbolic Processes. Hillsdale, NJ: Lawrence Erlbaum Associates. 1982. See Hayek's essay, "The Sensory Order after 25 Years", and "Discussion".

External links

• Discussion of Popper's Life and Work from Philosophy Talk Radio Program
• Stephen Thornton, "Karl Popper", in The Stanford Encyclopedia of Philosophy (Summer 2009 Edition), Edward N. Zalta (ed.).
• Karl Popper from Stanford Encyclopedia of Philosophy
• Popper, K. R. ‘‘“Natural Selection and the Emergence of Mind”’’, 1977.
• The Karl Popper Web
• Sir Karl Popper Society International Association for the Promotion of Science and Research, in German
• University of Canterbury (NZ) brief biography of Popper
• Audio recordings of Karl Popper speaking
• Influence on Friesian Philosophy
• Open Society Institute George Soros foundations network
• Sir Karl R. Popper in Prague, May 1994
• Synopsis and background of The poverty of historicism
• "A Skeptical Look at Karl Popper" by Martin Gardner
• "A Sceptical Look at 'A Skeptical Look at Karl Popper'" by J C Lester.
• Sir Karl Popper: Science: Conjectures and Refutations
• Information on Lakatos/Popper Site maintained by John Kadvany, PhD.
• Discovering Karl Popper by Peter Singer The New York Review of Books, vol. 21, no. 7 (2 May 1974)
• An interview with Karl Popper. Persian translation by Khosro Naghed
• Karl Popper on Information Philosopher
• Karl Popper (Il Diogene) (it)

Popper on In Our Time at the BBC, 8 February 2007. Discussion with John Worrall, Professor of Philosophy of Science at the London School of Economics, Anthony O'Hear, Weston Professor of Philosophy at Buckingham University, Nancy Cartwright, Professor of Philosophy at the LSE and the University of California, hosted by Melvyn Bragg.

• History of Twentieth-Century Philosophy of Science, BOOK V: Karl Popper Site offers free downloads by chapter available for public use.
• Karl Popper Archive at LSE British Library This is a microfilm copy of the Stanford University Popper Archive of Popper's papers to whose catalogue a weblink is provided.
• Karl Popper Archive at University Library Klagenfurt, consists of Popper's Library and paper copies of the Popper Papers at The Hoover Institution Archive at Stanford, California
• Austrian Karl R. Popper Research Association, University of Graz, Austria
• Sound recordings from the Sir Karl R. Popper papers at the Hoover Institution Archives.

See also: Popper