The demarcation problem in the philosophy of science is about how and where to draw the lines around science. The boundaries are commonly drawn between science and non-science, between science and pseudoscience, between science and philosophy and between science and religion.^[1] A form of this problem, known as the generalized problem of demarcation subsumes all four cases.

After over a century of dialogue among philosophers of science and scientists in varied fields, and despite broad agreement on the basics of scientific method,^[2] the boundaries between science and non-science continue to be debated.^[3]

History[link]

Demarcation in Greek science[link]

An early attempt at demarcation can be seen in the efforts of Greek natural philosophers and medical practitioners to distinguish their methods and their accounts of nature from the mythological or mystical accounts of their predecessors and contemporaries.^[4] G. E. R. Lloyd notes that there was a sense in which the groups engaged in various forms of inquiry into nature set out to "legitimate their own positions,"^[5] laying "claim to a new kind of wisdom ... that purported to yield superior enlightenment, even superior practical effectiveness."^[6] Medical writers in the Hippocratic tradition maintained that their discussions were based on necessary demonstrations, a theme developed by Aristotle in his Posterior Analytics.^[7] One element of this polemic for science was an insistence on a clear and unequivocal presentation of arguments, rejecting the imagery, analogy, and myth of the old wisdom.^[8] Some of their claims to provide valid naturalistic explanations of phenomena do not stand up to close scrutiny.^[9]

Science and religion part ways[link]

Historically speaking, the relationship between science and religion has been complicated. Some scientists were very religious, and religion was often a chief motivator and sponsor of scientific investigation. However, towards the end of the 19th century, science and religion came to be seen by the public as being increasingly at odds, a gradual phenomenon which came to a head around the debates over the work on evolution produced by Charles Darwin. Precursors and preconditions for the apparent split did exist before Darwin's publication of The Origin of Species, but it was this work which brought the debate into the popular British press and became a figurehead for the tensions between science and religion among certain groups (a position it still holds for some today). In 1874, the influential science historian John William Draper published his History of the Conflict between Religion and Science. In it he portrayed the entire history of scientific development as a war against religion. This view was propagated further by such prestigious followers as Andrew Dickson White in his essay A History of the Warfare of Science with Theology in Christendom (1896).

The work by Draper and White must be seen as directly coming out of this social climate, and their model of science and religion as being eternally opposed, if not historically accurate, became a dominant social trope.^[10] Sociologists of science have studied the attempts to erect hard distinctions between science and non-science as a form of boundary-work, emphasizing the high stakes for all involved in such activities.

Logical Positivism[link]

This new conception of science as something not only independent from religion, but actually opposed to it raised the inevitable question of what separates the two. Among the first to develop an answer were the members of the Vienna Circle. Their philosophical position, known as Logical positivism, espoused a theory of meaning which held that only statements about empirical observations and formal logical propositions are meaningful, effectively asserting that statements which are not derived in this manner (including religious and metaphysical statements) are by nature meaningless (see the verifiability theory of meaning also known as verificationism).

Falsificationism[link]

The philosopher Karl Popper noticed that the philosophers of the Vienna Circle had mixed two different problems and had accordingly given them a single solution: verificationism. In opposition to this view, Popper emphasized that a theory might well be meaningful without being scientific, and that, accordingly, a criterion of meaningfulness may not necessarily coincide with a criterion of demarcation. His own falsificationism, thus, is not only an alternative to verificationism; it is also an acknowledgment of the conceptual distinction that previous theories had ignored.

Popper saw demarcation as a central problem in the philosophy of science. In place of verificationism he proposed falsification as a way of determining if a theory is scientific or not. If a theory is falsifiable, then it is scientific; if it is not falsifiable, then it is not science. Falsifiability was one of the criteria used by Judge William Overton to determine that 'creation science' was not scientific and should not be taught in Arkansas public schools (see McLean v. Arkansas).

Falsifiability is a property of statements and theories, and is itself neutral. As a demarcation criterion, it seeks to take this property and make it a base for affirming the superiority of falsifiable theories over non-falsifiable ones as a part of science, in effect setting up a political position that might be called falsificationism. However, much that would be considered meaningful and useful is not falsifiable(reference). Certainly non-falsifiable statements have a role in scientific theories themselves. What the Popperian criterion allows to be called scientific is open to interpretation. A strict interpretation would concede too little since there are no scientific theories of interest that are completely free of anomalies. Conversely, if we do not consider the falsifiability of an assumption or theory and the willingness of an individual or group to obtain or accept falsifying instances, we would then permit almost any assumption or theory.

It is nevertheless very useful to know if a statement or theory is falsifiable, if for no other reason than it provides us with an understanding of the ways in which one might assess the theory.

Kuhn and paradigm shifts[link]

Thomas Kuhn, an American historian of science, has proven very influential in the philosophy of science, and is often connected with what has been called postpositivism or postempiricism. In his 1962 book The Structure of Scientific Revolutions, Kuhn divided the process of doing science into two different endeavors, which he called normal science and extraordinary science (which he sometimes also called revolutionary science). The process of "normal" science is what most scientists do while working within what he calls the current accepted paradigm of the scientific community, and within this context Karl Popper's ideas on falsification as well as the idea of a scientific method still have some currency. This sort of work is what Kuhn calls "problem solving": working within the bounds of the current theory and its implications for what sorts of experiments should or should not be fruitful. However, during the process of doing "normal" science, Kuhn claimed, anomalies are generated, some of which lead to an extension of the dominant "paradigm" in order to explain them, and others for which no satisfactory explanation can be found within the current model. When enough of these anomalies have accumulated, and scientists within the field find them significant (often a very subjective judgment), a "crisis period" is begun, Kuhn argues, and some scientists begin to participate in the activity of "extraordinary" science. In this phase, it is recognized that the old model is fundamentally flawed and cannot be adapted to further use, and totally new (or often old and abandoned) ideas are looked at, most of which will be failures. But during this time, a new "paradigm" is created, and after a protracted period of "paradigm shift," the new paradigm is accepted as the norm by the scientific community and integrated into their previous work, and the old paradigm is banished to the history books. The classic example of this is the shift from Maxwellian/Newtonian physics to Einsteinian/Quantum physics in the early 20th century. If the acceptance or failure of scientific theories relied only on simple falsification, according to Kuhn, then no theory would ever survive long enough to be fruitful, as all theories contain anomalies.

The process by which Kuhn said a new paradigm is accepted by the scientific community at large does indicate one possible demarcation between science and pseudoscience. Rejecting Popper's simple model of falsification, Kuhn argued instead that a new paradigm is accepted mainly because it has a superior ability to solve problems that arise in the process of doing normal science. That is, the value of a scientific paradigm is its predictive power and its ability to suggest solutions to new problems while continuing to satisfy all of the problems solved by the paradigm that it replaces. Pseudoscience can then be defined by a failure to provide explanations within such a paradigm.

Demarcation is problematic when standard scientific ways (experiments, logic, etc.) of assessing a theory or a hypothesis cannot be applied for some reason. An example would be trying to identify what is currently science in the domains of meteorology or medicine. The argument goes that these domains are not unlike early astrology in several ways, which was once considered a science. Astrology did not conflict with other known facts at the time, it occasionally failed to make accurate predictions, and certain gaps in knowledge of the causal mechanisms were tolerated.^{[11] [12]}

Feyerabend and the problem of autonomy in science[link]

There has been a post-Kuhn trend to downplay the difference between science and non-science, as Kuhn's work largely called to question the Popperian ideal of simple demarcation, and emphasized the human, subjective quality of scientific change. The radical philosopher of science Paul Feyerabend took these arguments to their limit, arguing that science does not occupy a special place in terms of either its logic or method, so that any claim to special authority made by scientists cannot be upheld. This leads to a particularly democratic and anarchist approach to knowledge formation. He claimed that there can be found no method within the history of scientific practice which has not been violated at some point in the advancing of scientific knowledge. Both Lakatos and Feyerabend suggest that science is not an autonomous form of reasoning, but is inseparable from the larger body of human thought and inquiry. If so, then the questions of truth and falsity, and correct or incorrect understanding are not uniquely empirical.^{[citation needed]} Many meaningful questions can not be settled empirically — not only in practice, but in principle.^{[citation needed]}

According to this way of thinking, the difficulty string theorists have had in applying experimental science would not bring in to question their status as scientists, but rather as metaphysicians.

Thagard's method[link]

Paul R. Thagard has proposed another set of principles to try to overcome these difficulties, and believes it is important for society to find a way of doing so. According to Thagard's method, a theory is not scientific if it satisfies two conditions:

1. It is unpromising: The theory has been less progressive than alternative theories over a long period of time, and faces many unsolved problems; and...
2. The Scientific Method is not being adhered to: The community of practitioners makes little attempt to develop the theory towards solutions of the problems, shows no concern for attempts to evaluate the theory in relation to others, and is selective in considering confirmations and disconfirmations.^[13][14]

Thagard specifies that sometimes theories will spend some time as merely "unpromising" before they truly deserve the title of pseudoscience. He cites astrology as an example: it was stagnant compared to advances in physics during the 17th century, and only later became "pseudoscience" in the advent of alternative explanations provided by psychology during the 19th century.

Thagard also rejects that his criteria should be interpreted so narrowly as to allow ostrichism (willful ignorance of alternative explanations) or so broadly as to discount our modern science compared to science of the future. His definition is a practical one, which generally seeks to distinguish pseudoscience as theories that are stagnant and are not actively being scientifically investigated.

Laudan's rejection of the demarcation problem[link]

Larry Laudan concluded, after examining various historical attempts to establish a demarcation criterion, that "philosophy has failed to deliver the goods" in its attempts to distinguish science from non-science, to distinguish science from pseudoscience. None of the past attempts would be accepted by a majority of philosophers nor, in his view, should they be accepted by them or by anyone else. He noted that many well-founded beliefs are not scientific and, conversely, many scientific conjectures are not well-founded. He also found that demarcation criteria were historically used as "machines de guerre" in polemical disputes between "scientists" and "pseudo-scientists." Advancing a number of examples from everyday practice of football and carpentry and non-scientific scholarship such as literary criticism and philosophy, he saw the question of whether a belief is well-founded or not to be more practically and philosophically significant than whether it is scientific or not. In his judgment, the demarcation between science and non-science was a pseudo-problem that would best be replaced by focusing on the distinction between reliable and unreliable knowledge, without bothering to ask whether that knowledge is scientific or not. He would consign hollow phrases like "pseudo-science" or "unscientific" to the rhetoric of politicians or sociologists.^[15]

Demarcation in contemporary scientific method[link]

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The criteria for a system of assumptions, methods, and theories to qualify as science today vary in their details from application to application, and vary significantly among the natural sciences, social sciences and formal science. The criteria typically include (1) the formulation of hypotheses that meet the logical criterion of contingency, defeasibility, or falsifiability and the closely related empirical and practical criterion of testability, (2) a grounding in empirical evidence, and (3) the use of scientific method. The procedures of science typically include a number of heuristic guidelines, such as the principles of conceptual economy or theoretical parsimony that fall under the rubric of Ockham's razor. A conceptual system that fails to meet a significant number of these criteria is likely to be considered non-scientific.

Summary of salient characteristics of a scientific theory:^{[citation needed]}

• Reproducible. Makes predictions that can be tested by any observer, with trials extending indefinitely into the future.
• Falsifiable and testable. See Falsifiability and Testability.
• Consistent. Generates no obvious logical contradictions, and 'saves the phenomena', being consistent with observation.
• Pertinent. Describes and explains observed phenomena.
• Correctable and dynamic. Subject to modification as new observations are made.
• Integrative, robust, and corrigible. Subsumes previous theories as approximations, and allows possible subsumption by future theories. ("Robust", here, refers to stability in the statistical sense, i.e., not very sensitive to occasional outlying data points.) See Correspondence principle
• Parsimonious. Economical in the number of assumptions and hypothetical entities.
• Provisional or tentative. Does not assert the absolute certainty of the theory.

See also[link]

• Boundary-work

References[link]

Massimo Pigliucci.

Massimo Pigliucci (born January 16, 1964) is the chair of the Department of Philosophy at CUNY-Lehman College.^[1] He is also the editor in chief for the journal Philosophy & Theory in Biology.^[2] He is an outspoken critic of creationism and advocate of science education.

Biography[link]

Pigliucci was born in Monrovia, Liberia, although he was raised in Rome, Italy.^[3] He has a doctorate in genetics from the University of Ferrara, Italy, a Ph.D. in botany from the University of Connecticut, and a Ph.D. in philosophy of science from the University of Tennessee.^[4] He is a fellow of the American Association for the Advancement of Science and of the Committee for Skeptical Inquiry.^[5]

Pigliucci was formerly a professor of ecology and evolution at Stony Brook University. He explored phenotypic plasticity, genotype-environment interactions, natural selection, and the constraints imposed on natural selection by the genetic and developmental makeup of organisms.^[6] Early in his career, he received the prestigious Theodosius Dobzhansky Prize^[7] from the Society for the Study of Evolution.^[8] As a philosopher, Pigliucci is interested in the structure and foundations of evolutionary theory, the relationship between science and philosophy, and the relationship between science and religion.^[9]

Pigliucci writes regularly for Skeptical Inquirer on topics such as climate change denial. He has also written for Philosophy Now and maintains a blog called "Rationally Speaking.^[10]" He has debated "deniers of evolution" (young-earth creationists and intelligent design proponents), including young earth creationists Duane Gish and Kent Hovind and intelligent design proponents William Dembski and Jonathan Wells, on many occasions.^{[11][12][13][14]}

Pigliucci is an atheist,^[15] and while he considers atheism a perfectly respectable metaphysical position, he believes that science does not necessarily demand atheism, because of the distinction between methodological and philosophical naturalism and the distinction between matters of fact and value judgments. He believes that many scientists and science educators fail to appreciate these differences.^[16]

Pigliucci serves on the board of NYC Skeptics and on the advisory board of the Secular Coalition for America.^[17] He also co-hosts its official podcast, Rationally Speaking, with Julia Galef.

Books[link]

• Nonsense on Stilts: How to Tell Science from Bunk (University of Chicago Press, 2010, ISBN 978-0-226-66786-7): This book presents a number of case studies on controversial topics in order to examine how science is conducted, how it is disseminated, how it is interpreted, and what it means to our society.
• Making Sense of Evolution (with Jonathan Kaplan, University of Chicago Press, 2006, ISBN 978-0-226-66837-6): A philosophical examination of the fundamental concepts of evolutionary theory and practice.
• Phenotypic Integration (Oxford University Press, 2003): A collection of technical essays on the evolution of complex biological organs.
• Denying Evolution: Creationism, Scientism, and the Nature of Science. (Sinauer, 2002): This book covers the evolution-creation controversy, better science teaching, and why people have difficulties with critical thinking. ISBN 0-87893-659-9
• Phenotypic Plasticity (Johns Hopkins University Press, 2001): A technical volume on research concerning nature-nurture questions.
• Tales of the Rational (Freethought Press, 2000): A series of essays on atheism, straw-man arguments, creationism and the like.
• Phenotypic Evolution (with Carl Schlichting, Sinauer, 1998): A technical volume on the current status and future prospects of evolutionary theory.

Articles[link]

The following are a few of his numerous articles. Some may be found at the Internet Infidels' Secular Web. Additional articles can be found on his web sites (see "External Links" below).

• Pigliucci, M. (2006). Is evolutionary psychology a pseudoscience? Skeptical Inquirer 30 (2):23-24.
• Pigliucci, M. (2005). Science and fundamentalism. EMBO reports 6: 1106-1109.[1]
• Pigliucci, M. (2005). The power and perils of metaphors in science. Skeptical Inquirer 29 (5):20-21.
• Pigliucci, M., J. Banta, et al. (2004). The alleged fallacies of evolutionary theory. Philosophy Now (46):36-39.
• Pigliucci, M. (2004). What is philosophy of science good for? Philosophy Now (44):45.

References[link]

External links[link]

• Plato's Footnote – Pigliucci's Webpage
• Rationally Speaking – blog by Pigliucci about skepticism and humanism.
• Dr. Pigliucci's Podcast
• Massimo Pigliucci on Secular Web
• Audio Interview with Dr. Massimo Pigliucci

Karl Popper
CH FRS FBA

Sir Karl Popper c. 1980s
Born	Karl Raimund Popper (1902-07-28)28 July 1902 Vienna, Austria-Hungary
Died	17 September 1994(1994-09-17) (aged 92) London, England
Era	20th century philosophy
Region	Western philosophy
School	Critical rationalism Liberalism
Main interests	Epistemology Rationality Philosophy of science Logic Social and political philosophy Philosophy of mind Philosophy of art Origin of life Interpretation of Quantum mechanics
Notable ideas	Critical rationalism Falsificationism Universal evolutionary trial and error model of life and knowledge Propensity interpretation Open society Cosmological pluralism Modified essentialism Axiomatic formalization of probability Active Darwinism Spearhead model Truthlikeness Objective Hermeneutics
Influenced by Socrates · Lycophron · Aristotle · Kant · Schopenhauer · Hegel  · Einstein · Kierkegaard · Wittgenstein · Vienna Circle · Hayek · Tarski · Selz · Russell · Campbell · Burke · Mill  · Hume  · Wächtershäuser
Influenced Virtually all philosophy of science since 1930s · Hayek · Friedman · Lakatos · Feyerabend · Soros · Miller · Agassi · Bartley · Gombrich · Jarvie · Dahrendorf · Levinson · Schmidt · Munz · Magee · Lorenz · Shearmur · Medawar · Dimitrakos · Albert · Gellner · Soroush · Taleb · Deutsch

Sir Karl Raimund Popper, CH FRS^[1] FBA (28 July 1902 – 17 September 1994) was an Austro-British^[2] philosopher and professor at the London School of Economics.^[3] He is generally regarded as one of the greatest philosophers of science of the 20th century;^[4][5] he also wrote extensively on social and political philosophy.

Popper is known for his attempt to repudiate the classical observationalist/inductivist form of scientific method in favour of empirical falsification. He is also known 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".^[6] In political discourse, he is known for his vigorous defence of liberal democracy and the principles of social criticism that he came to believe made a flourishing "open society" possible.

Personal life[link]

Karl Popper was born in Vienna (then in Austria-Hungary) in 1902, to upper middle-class parents. All of Karl Popper's grandparents were Jewish, but the Popper family converted to Lutheranism before Karl was born.^[7] 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^{[clarification needed]} 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).^[7]

Popper received a Lutheran upbringing and was educated at the University of Vienna.^[8] 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.^[9] Popper inherited both the library and the disposition from him.^[10]

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.^[11] After the June 15, 1919 street battle in the Hörlgasse, when police shot eight of his unarmed party comrades, he became disillusioned by what he saw to be the pseudo-scientific historical materialism of Marx, abandoned the ideology, and remained a supporter of social liberalism throughout his life.

In 1928, he earned a doctorate in psychology, under the supervision of Karl Bühler. His dissertation was entitled "Die Methodenfrage der Denkpsychologie" (The question of method in cognitive psychology).^[12] Then, from 1930 to 1936, he 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.

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). It was here that he wrote his influential work The Open Society and its Enemies. 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.^[1] 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,^[1] 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.^[13]

Philosophy[link]

Philosophy of science[link]

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Falsifiability[link]

Popper coined the term "critical rationalism" to describe his philosophy. The term indicates his rejection of classical empiricism, and 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 made false, but rather that, if it is false, it 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 — that is, 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:

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In response to a given problem situation (Failed to parse (Missing texvc executable; please see math/README to configure.): PS_1 ), a number of competing conjectures, or tentative theories (Failed to parse (Missing texvc executable; please see math/README to configure.): TT ), are systematically subjected to the most rigorous attempts at falsification possible. This process, error elimination (Failed to parse (Missing texvc executable; please see math/README to configure.): 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 (Failed to parse (Missing texvc executable; please see math/README to configure.): 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 (Failed to parse (Missing texvc executable; please see math/README to configure.): 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.

Truth[link]

As early as 1934, Popper wrote of the search for truth as "one of the strongest motives for scientific discovery."^{[citation needed]} 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:

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where Failed to parse (Missing texvc executable; please see math/README to configure.): Vs(a)

is the verisimilitude of a, Failed to parse (Missing texvc executable; please see math/README to configure.): CT_v(a)
is a measure of the content of truth of a, and Failed to parse (Missing texvc executable; please see math/README to configure.): 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.

Philosophy of arithmetic[link]

Popper's principle of falsifiability runs into prima facie difficulties when the epistemological status of mathematics is considered. It is difficult to conceive how simple statements of arithmetic, such as "2 + 2 = 4", could ever be shown to be false. If they are not open to falsification they can not be scientific. If they are not scientific, it needs to be explained how they can be informative about real world objects and events.

Popper's solution ^[14] was an original contribution in the philosophy of mathematics. His idea was that a number statement such as "2 apples + 2 apples = 4 apples" can be taken in two senses. In one sense it is irrefutable and logically true, in the second sense it is factually true and falsifiable. Concisely, the pure mathematics "2 + 2 = 4" is always true, but, when the formula is applied to real world apples, it is open to falsification.^[15]

Political philosophy[link]

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Liberalism
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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",^{[citation needed]} 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 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[link]

Although Popper was an advocate of toleration, he said that intolerance should not be tolerated, for if tolerance allowed intolerance to succeed completely, tolerance itself would be threatened. In The Open Society and Its Enemies, he argued:

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.^{[citation needed]}

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."^{[citation needed]} 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.^{[citation needed]}

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.^[16]

Problem of induction[link]

Among his contributions to philosophy is his attempt to answer the philosophical problem of induction. Popper claims to have found a solution to the problem of induction. 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 identified as all 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; it is more important that their falsity can be detected as easily as possible.

Popper and David 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. He writes, "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[link]

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.^[17]

When he gave the second Arthur Holly Compton Memorial Lecture in 1965, 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.^[18]

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.^[19]

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, saying, "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."^[20]

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.^[21]

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

Influence[link]

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."^[22] 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."^[23]

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. One of Popper's students at the London School of Economics was the billionaire investor George Soros,^{[citation needed]} among whose philanthropic foundations is the Open Society Institute, a think-tank named in honor of Popper's The Open Society and Its Enemies.^{[citation needed]}

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.

Darwinism[link]

The creation–evolution controversy in the United States raises the issue of whether creationistic ideas may be legitimately called science and whether evolution itself may be legitimately called science. In the debate, both sides and even courts in their decisions have frequently invoked Popper's criterion of falsifiability. In this context, passages written by Popper are frequently quoted in which he speaks about such issues himself. For example, he famously stated "Darwinism is not a testable scientific theory, but a metaphysical research program — a possible framework for testable scientific theories." 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.^[24]

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."^[25]

Popper 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.^[25]

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:

My 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.^[25]

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.^[26]

These frequently quoted passages are only a very small part of what Popper wrote on the issue of evolution, however, and give the wrong impression that he mainly discussed questions of its falsifiability. Popper never invented this criterion to give justifiable use of words like science. In fact, Popper says at the beginning of Logic of Scientific Discovery that it is not his plan to define science, and that science can in fact be defined quite arbitrarily.

Popper had his own sophisticated views on evolution that go much beyond what the frequently-quoted passages say.^[27] In effect, Popper agreed with some of the points of both creationists and naturalists, but also disagreed with both views on crucial aspects. Popper understood the universe as a creative entity that invents new things, including life, but without the necessity of something like a god, especially not one who is pulling strings from behind the curtain. He said that evolution must, as the creationists say, work in a goal-directed way^[28] but disagreed with their view that it must necessarily be the hand of god that imposes these goals onto the stage of life.

Instead, he formulated the spearhead model of evolution, a version of genetic pluralism. According to this model, living organisms themselves have goals, and act according to these goals, each guided by a central control (in its most sophisticated form, this is the brain of humans, but controls also exist in much less sophisticated ways for species of lower complexity, such as the amoeba). These goals bring the purpose into the world. Mutations in the genes that determine the structure of the control may then cause drastic changes in behaviour, preferences and goals, without having an impact on the organism's phenotype. Popper postulates that such purely behavioral changes are less likely to be lethal for the organism compared to drastic changes of the phenotype.^{[citation needed]}

Popper contrasts his views with the notion of the "hopeful monster" that has large phenotype mutations and calls it the "hopeful behavioral monster". After behavior has changed radically, small but quick changes of the phenotype follow to make the organism fitter to its changed goals. This way it looks as if the phenotype were changing guided by some invisible hand, while it is merely natural selection working in combination with the new behaviour. For example, according to this hypothesis, the eating habits of the giraffe must have changed before its elongated neck evolved. Popper contrasted this view as evolution from within (the organism actively trying to discover new ways of life and being on a quest for conquering new ecological niches), with the naturalistic evolution from without (which has the picture of a hostile environment only trying to kill the mostly passive organism, or perhaps segregate some of its groups).

Popper's view is somewhat compatible with the central tenets of Intelligent Design, claiming that the intelligent cause seen as necessary by ID is simply natural (the intelligence of living beings themselves), not supernatural.

Popper was a key figure encouraging patent lawyer Günter Wächtershäuser to publish his iron–sulfur world theory on abiogenesis and his criticism of "soup" theory.

Criticism[link]

Philosophy of science[link]

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.^[29]

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”.^{[dubious – discuss]}

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]^[30]

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'.^[31] (But Popper criticised what he saw as Kuhn's relativism.^[32]) 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.^[33]

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.^[34]

Other criticism[link]

It has been argued that Popper's student Imre Lakatos transformed Popper's philosophy using historicism and updated Hegelian historiographic ideas.^[35][36]

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.^[37][38]

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".^[39] 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."^[40]

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.^[41]

According to John N. Gray, Popper held that "a theory is scientific only in so far as it is falsifiable, and should be given up as soon as it is falsified." ^[42] By applying Popper's account of scientific method, Gray's Straw Dogs states that this would have "killed the theories of Darwin and Einstein at birth." When they were first advanced, Gray claims, each of them was "at odds with some available evidence; only later did evidence become available that gave them crucial support."^[43] Against this, Gray seeks to establish the irrationalist thesis that "the progress of science comes from acting against reason." ^[44]

Gray does not, however, give any indication of what available evidence these theories were at odds with, and his appeal to "crucial support" illustrates the very inductivist approach to science that Popper sought to show was logically illegitimate. For, according to Popper, Einstein's theory was at least equally as well corroborated as Newton's upon its initial conception; they both equally well accounted for all the hitherto available evidence. Moreover, since Einstein also explained the empirical refutations of Newton's theory, general relativity was immediately deemed suitable for tentative acceptance on the Popperian account.^[45] Indeed, Popper wrote, several decades before Gray's criticism, in reply to a critical essay by Imre Lakatos:

"It is true that I have used the terms "elimination", and even "rejection" when discussing "refutation". But it is clear from my main discussion that these terms mean, when applied to a scientific theory, that it is eliminated as a contender for the truth- that is, refuted, but not necessarily abandoned. Moreover, I have often pointed out that any such refutation is fallible. It is a typical matter of conjecture and of risk-taking whether or not we accept a refutation and, furthermore, of whether we "abandon" a theory or, say, only modify it, or even stick to it, and try to find some alternative, and methodologically acceptable, way round the problem involved. That I do not conflate even admitted falsity with the need to abandon a theory may be seen from the fact that I have frequently pointed out, that Einstein regarded general relativity as false, yet as a better approximation to the truth than Newton's gravitational theory. He certainly did not "abandon" it. But he worked to the end of his life in an attempt to improve upon it by way of a further generalization."^[46]

Gravesite on the Wiener Küniglberg

See also[link]

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

References[link]

Bibliography[link]

Further reading[link]

External links[link]

Wikiquote has a collection of quotations related to: Karl Popper

Wikimedia Commons has media related to: Karl Popper

• 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
• 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. (listen now), 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.