Karl Popper

Sir Karl Raimund Popper CH, M.A., Ph.D., D.Litt., FBA, FRS (July 28 1902 – September 17 1994), was one of the most influential philosophers of science of the 20th century. He rejected the classical observationalist-inductivist account of scientific method by advancing empirical falsifiability as the criterion for distinguishing science from non-science (i.e., pseudoscience and metaphysics); he is also well known for his defense of liberal democracy and the principles of social criticism which he considered to be important for the "open society" to flourish.

Popper wrote his political philosophy opus The Open Society and Its Enemies at the University of Canterbury (shown) in New Zealand, far from the strife of war-torn Europe

Life

Popper was born in Vienna (then in Austria-Hungary) in 1902 to middle-class parents of Jewish origins who had converted to Christianity. His father was a bibliophile, said to have 10,000 volumes in his library at home. Popper was brought up as a Lutheran, and studied at the University of Vienna. He took a PhD in Philosophy in 1928, and taught in secondary school from 1930 to 1936.

In 1934 he published his first book, Logik der Forschung (The Logic of Scientific Discovery), in which he proposed his theory of potential falsifiability as the criterion for what should be considered 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 (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 in 1965, and was elected a Fellow of the Royal Society in 1976. He retired from academic life in 1969, but remained intellectually active until his death in 1994. 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, 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, and Darwin College Cambridge. Austria awarded him the Grand Decoration of Honour in Gold.

Popper's philosophy

Philosophy of science

Popper described his philosophy as critical rationalism, indicating his rejection of classical empiricism, and the observationalist-inductivist account of science that had grown from it. Popper held that scientific theories are universal, and can be tested only by reference to their implications. He also held that scientific theory (and human knowledge generally) is irreducibly conjectural, generated by creative imagination to solve problems that arise in specific historico-cultural settings. Logically, no number of positive outcomes at the level of experimental testing can prove the truth of a scientific theory, but a single counterexample is logically decisive in showing the theory to be false. Popper's account of the logical asymmetry between verification and falsification is at the heart of his philosophy of science. It also led him to take falsifiability as his criterion of demarcation between what is and is not scientific: a theory should be considered scientific if and only if it is falsifiable. He thus attacked the foundations of psychoanalysis and Marxism on the grounds that their explanations are not falsifiable. Popper also argued against the Copenhagen interpretation of quantum mechanics. He disagreed with Niels Bohr's instrumentalism and supported Albert Einstein's realist approach to scientific theories about the universe. Popper's falsificationism resembles Charles Peirce's fallibilism. In Of Clocks and Clouds (1966), Popper said he wished he had known of Peirce's work earlier.

In All Life is Problem Solving, Popper tried to explain why our understanding of the universe seems to improve over time. If the truth of our theories cannot be proved scientifically, how is it that the growth of science results in a growth in knowledge? In Popper's view, the advance of scientific knowledge is an evolutionary process characterised by:

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

In response to a given problem ($PS_{1}$), several competing conjectures, or tentative theories ($TT$), are subjected to rigorous attempts at falsification. This process, error elimination ($EE$), performs a similar function for science that natural selection performs in evolution. Theories that better survive the process are not more true, but rather, more "fit"—' 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, just as biological evolution has produced, over time, adaptive traits equipped to deal with more and more complex problems of survival, similarly, the evolution of theories through the scientific method may, in Popper's view, reflect a type of progress toward 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 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 (Its first published form was 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 to Popper 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. 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 examples such as the one described above which 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 between:

1. "John called" is true.

and

1. "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."

On 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 notion of verisimilitude.

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

The simplest mathematical formulation that Popper gives of this concept is in the tenth chapter of Conjectures and Refutations, where he defines it as:

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

where $Vs(a)$ is the verisimilitude (or truthlikeness) 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:

1. World One, the phenomenal world, the world of direct experience;
2. World Two, the world of mind, or mental states, ideas, and perceptions; and
3. World Three, 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 mind). World Three, he argued, was the product of individual human beings in the 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 an individual mind owes at least as much to the 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' and liberal democracy. Historicism, as Popper was using the term, is the theory that history develops according to general laws towards a determinate end, what historians would call teleological determinism. Popper argued that this view is the principal theoretical presupposition underpinning most forms of authoritarianism and totalitarianism. He argued that form of historicism is based upon mistaken assumptions regarding the nature of scientific law and prediction. As the growth of human knowledge is a causal factor in the evolution of human history, and because "no society can predict, scientifically, its own future states of knowledge", he argued, that there can be no predictive science of human history.

Problem of induction

Among his contributions to philosophy is his answer to David Hume's Problem of Induction. Hume stated that just because the sun has risen every day for as long as anyone can remember, doesn't mean that there is any rational reason to believe it will come up tomorrow. There is no rational way to prove that a pattern will continue on just because it has before. Popper's reply is that although we cannot prove that the sun will come up, we can theorize that it will. If it does not come up, then it will be disproven, but until the theory is disproven we can accept it. Thus, Popper's demarcation between science and non-science serves as an answer to an old logical problem as well. This approach was criticised by Peter Singer for masking the role induction plays in empirical discovery.

Influence

Popper played a vital role in establishing the philosophy of science as an autonomous discipline within analytic philosophy, through his own works, and also through his influence on his contemporaries. Popper founded in 1946 the Department of Philosophy, Logic and Scientific Method at the London School of Economics and there influenced both Imre Lakatos and Paul Feyerabend, two important philosophers of science in the next generation of analytic philosophy. (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.)

Popper had a long and close friendship with economist Friedrich Hayek, who was also brought to the London School of Economics from Vienna. 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 arguing that children and adults should try to resolve their differences without coercion.

Political philosopher Ayaan Hirsi Ali stated that her ideas of liberalism had been influenced by Popper's The Open Society and its Enemies.

Critics

The Quine-Duhem thesis argues that it's impossible to test a single hypothesis on its own, as each one comes as part of an environment of theories. Thus we can only say that the 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 The Logic of Scientific Discovery. For Popper, theories are accepted or rejected via a sort of 'natural selection'. 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 Conjectures and Refutations: The Growth of Scientific Knowledge, Popper writes, "[S]cience 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 proffering instructions that merely need to be followed diligently to achieve science, Popper makes clear in The Logic of Scientific Discovery his belief that the resolution of conflicts between hypotheses and observations can only be a matter of the collective judgement of scientists.

Other critics seek to vindicate the claims of historicism 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 baseless, but are received with an attention and respect that their "intrinsic worth hardly merits".

In 2004 philosopher and psychologist Michel ter Hark (Groningen, The Netherlands) published a book, called Popper, Otto Selz and the rise of evolutionary epistemology, in which he claims that Popper got some of his ideas from his tutor, the German-Jewish psychologist Otto Selz. Selz never published his ideas, partly because of the rise of Nazism which forced him to quit his work in 1933, and the prohibition of referencing to Selz' work.