Karl Popper

Sir Karl Raimund Popper CH FRS FBA
Era	20th century philosophy
Region	Western Philosophy
School	Analytic Critical rationalism · Fallibilism Evolutionary epistemology
Main interests	Epistemology Philosophy of science Social and political philosophy
Notable ideas	Falsifiability Hypothetico-deductive method Open society

Sir Karl Raimund Popper CH, FRS,FBA(July 28 1902 – September 17 1994) was an Austrian and British philosopher and a professor at the London School of Economics. He is counted among the most influential philosophers of science of the 20th century, and also wrote extensively on social and political philosophy. Popper is known for repudiating 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 which he took to make the flourishing of the "open society" possible.

Life

Karl Popper was born in Vienna (then in Austria-Hungary) in 1902 to middle-class parents of Jewish origins, both of whom had converted to Christianity. Popper received a Lutheran upbringing and was educated at the University of Vienna.. His father was 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 he became attracted by Marxism and subsequently joined the Association of Socialist School Students and also became a member of the Social Democratic Party of Austria, which was at that time a party that fully adopted the marxist ideology. He soon became disillusioned by the philosophical restraints imposed by the historical materialism of Marx, abandoned the ideology and remained a passive supporter of social liberalism throughout his life.

In 1928 he earned a doctorate in Psychology and taught secondary school from 1930 to 1936. He 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.

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, where he was appointed professor in 1949. He 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.

Gravesite of Sir Karl Popper in Lainzer Friedhof, Vienna, Austria.

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 of Honour in Gold. He died in 1994. After cremation, Popper's ashes were taken to Vienna and buried at Lainz 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 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 historico-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. 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 the theories enshrined by them 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 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. 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 characterised 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 fit" does not predict 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-criticised 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'. Historicism is the theory that history develops inexorably and necessarily according to knowable general laws towards a determinate end. Popper 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 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 allow one to justifiably make 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.

Problem of Induction

Among his contributions to philosophy is his attempt to answer the philosophical problem of induction. 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's 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, we can formulate a theory that every day the sun will rise—if it does not rise on some particular day, our theory will be disproved, but at present it is confirmed. Since it is a very well-tested theory, we have every right to believe that it accurately represents reality, so far as we know.

This may be a true description of the pragmatic approach to knowledge adopted by the scientific method, but it does not in itself address the philosophical problem. As Stephen Hawking explains, "No matter how many times the results of experiments agree with some theory, you can never be sure that the next time the result will not contradict the theory." It may be pragmatically useful to accept a well-tested theory as true until it is falsified, but this does not solve the philosophical problem of induction. As Bertrand Russell put it, "the general principles of science . . . are believed because mankind have found innumerable instances of their truth and no instances of their falsehood. But this affords no evidence for their truth in the future, unless the inductive principle is assumed." In essence, Popper addressed justification for belief ("why do you believe") that the sun will rise tomorrow, not justification for the fact ("how do you know") that it will, which is the crux of the philosophical problem. Said another way, Popper addressed the psychological causes of our belief in the validity of induction without trying to provide logical reasons for it. In this way, he provided a psychological account of the use of induction, but left the philosophical ground of induction as a valid mode of knowledge unaccounted for.

Issue of Darwinism

Karl Popper famously stated "Darwinism is not a testable scientific theory, but a metaphysical research program." In the same paper, 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."

Influence

By all accounts, Popper has 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." (See Hacohen, 2000). 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." (See Weimer and Palermo, 1982).

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 multibillionaire investor George Soros, who says his investment strategies are modelled on Popper's understanding of the advancement of knowledge through 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 movement which noticed that Popper's general theory of knowledge creation does not differentiate between adults and children, and that all previous theories of learning contradict Popperian epistemology.

Critics

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 (Brian Magee 1973: Popper (Modern Masters series)).

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 found little evidence of scientists actually following a falsificationist methodology. 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 seems to have anticipated Kuhn's observations. 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 that 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, by asking about statements such as "There are black holes", which cannot be falsified by any possible observation, yet which seems to be a legitimately scientific claim. Similarly, it's not clear how Popper would deal with a statement like "for every metal, there is a temperature at which it will melt", which can neither be confirmed nor falsified by any possible observation, yet which 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.

Other criticisms

Other critics seek to vindicate the claims of historicism or holism to intellectual respectability, or psychoanalysis or Marxism to scientific status. It has been argued that Popper's student Imre Lakatos, for example, transformed Popper's philosophy using historicist and updated Hegelian historiographic ideas.

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 0521830745, in which he claimed that Popper took some of his ideas from his tutor, the German-Jewish 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.

See also

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

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 0415394317
• The Logic of Scientific Discovery, 1934 (as Logik der Forschung, English translation 1959), ISBN 0415278449
• 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 0415065690
• The Open Society and Its Enemies, 1945 Vol 1 ISBN 0415290635, Vol 2 ISBN 0415290635
• Quantum Theory and the Schism in Physics, 1956/57 (as privately circulated galley proofs; published as a book 1982), ISBN 0415091128
• The Open Universe: An Argument for Indeterminism, 1956/57 (as privately circulated galley proofs; published as a book 1982), ISBN 0415078652
• Realism and the Aim of Science, 1956/57 (as privately circulated galley proofs; published as a book 1983), ISBN 0091514509
• Conjectures and Refutations: The Growth of Scientific Knowledge, 1963, ISBN 0415043182
• Objective Knowledge: An Evolutionary Approach, 1972, Rev. ed., 1979, ISBN 0198750242
• Unended Quest; An Intellectual Autobiography, 1976, ISBN 0415285909
• The Self and Its Brain: An Argument for Interactionism (with Sir John C. Eccles), 1977, ISBN 0415058988
• Natural Selection and the Emergence of Mind article by Popper, Dialectica 1978
• In Search of a Better World, 1984, a collection of Popper’s essays and lectures covering a range of subjects from the beginning of scientific speculation in classical Greece to the need for a new professional ethic based on the ideas of tolerance and intellectual responsibility; "All things living are in search of a better world."; Karl Popper, from the Preface of the book. ISBN 0415135486
• Die Zukunft ist offen (The Future is Open) (with Konrad Lorenz), 1985 (in German), ISBN 349200640X
• A World of Propensities, 1990, ISBN 1855060000
• The Lesson of this Century, Interviewer: Giancarlo Bosetti, English translation: Patrick Camiller), 1992, ISBN 0415129583
• All life is Problem Solving, 1994, ISBN 0415249929
• The Myth of the Framework: In Defence of Science and Rationality, (Edited by Mark Amadeus Notturno) 1994, ISBN 0415135559
• Knowledge and the Mind-Body Problem: In Defence of Interactionism, (Edited by Mark Amadeus Notturno) 1994
• The World of Parmenides, Essays on the Presocratic Enlightenment, 1998, (Edited by Arne F. Petersen with the assistance of Jørgen Mejer), ISBN 0415173019
• 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)
• After 'The Open Society': Selected Social and Political Writings, 2008 (Edited by Jeremy Shearmur and Piers Norris Turner, it includes previously unpublished and uncollected essays), ISBN 0415309085

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.)
• David Miller. Critical Rationalism: A Restatement and Defence. 1994.
• David Miller (Ed.). Popper Selections.
• John W. N. Watkins. Science and Skepticism. 1984.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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

• Let theory pass on, not human. Documentary about Karl Popper on North German Broadcasting Cooperation Norddeutscher Rundfunk (in German)
• Discussion of Popper's Life and Work from Philosophy Talk Radio Program
• Karl Popper from Stanford Encyclopedia of Philosophy
• The Karl Popper Web
• Karl Popper Institute includes complete bibliography 1925-1999
• 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
• "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 (May 2, 1974)
• An interview with Karl Popper. Persian translation by Khosro Naghed
• Karl Popper (Il Diogene) (it)
• "Karl Popper", BBC Radio 4 programme, In Our Time, 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.
• http://www.uni-klu.ac.at/ub/sondersammlungen/karl-popper-sammlung/index.html (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, Cal.)
• http://www.karlpopper.info (Austrian Karl R. Popper Research Association - University of Graz, Austria)