Popper formulates and explains his non-justificationist theory of knowledge. Science--empirical science--aims at true explanatory theories, yet it can never prove, finally establish, or justify any of its theories as true, not even if it is in fact a true theory. Science must continue to question and criticize all its theories, even those which happen to be true.

A sampling of the philosophical writings of Karl Popper includes discussions of rationalism, knowledge, human freedom, and the scientific method.

The way in which knowledge progresses, and especially our scientific knowledge, is by unjustified (and unjustifiable) anticipations, by guesses, by tentative solutions to our problems, by conjectures. These conjectures are controlled by criticism: that is, by attempted refutations, which include severely critical tests. They may survive these tests; but they can never be positively justified: they can neither be established as certainly true nor even as 'probable' (in the sense of the probability calculus). Criticism of our conjectures is of decisive (...) importance: by bringing out our mistakes it makes us understand the difficulties of the problems which we try to solve. This is how we become better acquainted with our problem, and able to propose more mature solutions: the very refutation of a theory - that is, of a tentative solution to our problem - is always a step forward that takes us nearer the truth. And this is how we can learn from our mistakes. As we learn from our mistakes our knowledge grows, even though we may never know - that is, know for certain. Since our knowledge can grow, there can be no reason here for despair of reason. And since we can never know for certain, the can be no authority here for any claim to authority, for conceit over our knowledge, or for smugness. The essays and lectures of which this book is composed apply this thesis to many topics, ranging from problems of the philosophy and history of the physical and social sciences to historical and political problems. (shrink)

We express here the statement » The probability of a given b equals r « symbolically by » p = r «. A formal axiomatic calculus can be constructed comprising all the well‐known laws of probability theory. This calculus can be interpreted in various ways. The present paper is a criticism of the subjective interpretation; that is to say, of any interpretation which assumes that probability expresses degrees of incomplete knowledge: a is the statement incompletely known, b is our total (...) knowledge, and p is the degree to which a is entailed by b. The subjective interpretation has often been proposed as an explanation and even a sharpening of the various objective theories . It is shown in the paper that this proposal cannot be realised because the subjective theory cannot lead to results which are compatible with the objective theory. This is due to various reasons, the most important of which is that the objective theory interprets » b « in » p « as a statement of the objective conditions of an experiment and » a « as one of its possible results. The subjective theory on the other hand interprets » b « as our total relevant knowledge which will in general include some knowledge of previous results of the experiment. It is shown that this must lead to incompatibility owing to the fact that this knowledge of previous results must influence the value of the probability.It is shown, in this way, that any probabilistic theory of the process of learning from experience—that is to say, any probabilistic theory of induction—must lead to contradictions.RésuméL'énoncé: » La probabilité de a, si b est donné, est égale à r « est ici exprimé symboliquement par » p = r «. On peut construire un système axiomatique formel qui contient toutes les règles bien connues du calcul des probabilités. Ce calcul formel peut ětre interprété de manières très différentes. L'article contient une critique des interprétations subjectives, c'est‐à‐dire des interprétations qui admettent que la probabilité exprime des degrés de connaissance incomplète: a est un énoncé qu'on ne connaǐt que partiellement, b est notre connaissance totale, et p exprime le degré auquel a est implicitement contenu dans b. L'interprétation subjective a souvent été proposée comme une explication et un renforcement des différentes théories objectives . Dans cet article, l'auteur montre que ce projet n'est pas réalisable, car la théorie subjective mène à des résultats qui contredisent la théorie objective. Plusieurs circonstances sont responsables de cette situation; la plus importante, c'est que la théorie interprète le » b « dans » p « comme une description des conditions objectives d'une expérience . D'autre part, la théorie subjective interprète » b « comme notre savoir total , et ce savoir inclura en général des informations sur les résultats obtenus antérieurement pour cette expérience. L'auteur montre que ce fait conduit à une contradiction entre les deux interprétations, car cette connaissance doit avoir une influence sur la valeur subjective de la probabilité.A l'aide de ce raisonnement, on peut montrer que la théorie des probabilités appliquée au processus inductif tirant une expérience du domaine expérimental conduit à des contradictions.ZusammenfassungDie Aussage » Die Wahrscheinlichkeit von a, wenn b gegeben ist, ist gleich r « wird hier symbolisch durch » p = r « ausgedrückt. Ein formales Axiomensystem kann konstruiert werden, das alle die wohlbekannten Regeln der Wahrscheinlichkeitsrechnung enthält. Dieser formale Kalkül kann in sehr verschiedener Weise interpretiert werden. Der Artikel enthält eine Kritik der subjektiven Interpretationen; das heisst, jener Interpretationen die annehmen, dass die Wahrscheinlichkeit Grade von unvollständigem Wissen ausdrückt: a ist ein Satz der unvollständig gewusst wird, b ist unser Gesamtwissen, und p drückt den Grad aus zu dem a in b implizit enthalten ist. Die subjektive Interpretation wurde oft als eine Erklärung und Verschärfung der verschiedenen objektiven Theorien vorgeschlagen. In dem Artikel wird gezeigt, dass der Vorschlag undurchführbar ist, da die subjektive Theorie zu Resultaten führt, die der objektiven Theorie widersprechen. Verschiedene Umstände tragen zu dieser Situation bei. Der wichtigste dieser Umstände ist, dass die objektive Theorie das » b « in » p « als eine Beschreibung der objektiven Bedingungen eines Experimentes interpretiert . Andererseits interpretiert die subjektive Theorie » b « als unser Gesamtwissen , und dieses wird im allgemeinen Informationen bezüglich früherer Resultate dieses Experiments einschliessen. Es wird gezeigt, dass das zu einem Widerspruch zwischen den Interpretationen führt, da dieses Wissen Einfluss auf den subjektiven Wahrscheinlichkeitswert haben muss.Mit Hilfe dieses Gedankenganges wird gezeigt, dass die Wahrscheinlichkeitstheorie des induktiven Lernens aus der Erfahrung zu Widersprüchen führt. (shrink)

One of the most important books of the twentieth century, Karl Popper's The Open Society and Its Enemies is an uncompromising defense of liberal democracy and a powerful attack on the intellectual origins of totalitarianism. Popper was born in 1902 to a Viennese family of Jewish origin. He taught in Austria until 1937, when he emigrated to New Zealand in anticipation of the Nazi annexation of Austria the following year, and he settled in England in 1949. Before the annexation, (...) Popper had written mainly about the philosophy of science, but from 1938 until the end of the Second World War he focused his energies on political philosophy, seeking to diagnose the intellectual origins of German and Soviet totalitarianism. The Open Society and Its Enemies was the result. An immediate sensation when it was first published in two volumes in 1945, Popper's monumental achievement has attained legendary status on both the Left and Right and is credited with inspiring anticommunist dissidents during the Cold War. Arguing that the spirit of free, critical inquiry that governs scientific investigation should also apply to politics, Popper traces the roots of an opposite, authoritarian tendency to a tradition represented by Plato, Marx, and Hegel. In a substantial new introduction written for this edition, acclaimed political philosopher Alan Ryan puts Popper's landmark work in biographical, intellectual, and historical context. Also included is a personal essay by eminent art historian E.H. Gombrich, in which he recounts the story of the book's eventual publication despite numerous rejections and wartime deprivations. (shrink)

Fragen der Naturerkenntnis und Gedanken zu Geschichte und Politik.

‘If in this book harsh words are spoken about some of the greatest among the intellectual leaders of mankind, my motive is not, I hope, to belittle them. It springs rather from my conviction that, if our civilization is to survive, we must break with the habit of deference to great men.’ - Karl Popper, from the Preface Written in political exile during the Second World War and first published in two volumes in 1945, Karl Popper’s _The Open (...) Society and Its Enemies _is one of the most influential books of all time. Hailed by Bertrand Russell as a ‘vigorous and profound defence of democracy’, its now legendary attack on the philosophies of Plato, Hegel and Marx exposed the dangers inherent in centrally planned political systems and through underground editions become an inspiration to lovers of freedom living under communism in Eastern Europe. Popper’s highly accessible style, his erudite and lucid explanations of the thoughts of great philosophers and the recent resurgence of totalitarian regimes around the world are just three of the reasons for the enduring popularity of _The Open Society and Its Enemies_ and why it demands to be read today and in years to come. (shrink)

v. 1. The spell of Plato.--v. 2. The high tide of prophecy: Hegel, Marx, and the aftermath.

Many writers, both scientists and philosophers, when discussing the mind‐body problem, adopt what might be called the physicalist principle of the closedness of the physical world. They reject the possibility that the physical world is causally open to a realm of conscious experience that is not part of it.Among the upholders of such a view are those who may be called radical materialists or radical physicalists, who deny that there exists a realm of conscious experience. Also, there are the proponents (...) of various identity theories, who admit that there is such a realm, but claim that it may be in some sense identified with parts of the physical world.There are, however, other writers who accept the physicalist principle, but who nevertheless also accept that there exists a genuinely autonomous realm of conscious experience. Such writers often hold some form of panpsychism or epiphenomenalism, and in what follows these two views are briefly explained and critically discussed. (shrink)

Karl R. Popper; I.—Back to the Pre-Socratics: The Presidential Address, Proceedings of the Aristotelian Society, Volume 59, Issue 1, 1 June 1959, Pages 1–24, ht.

This article is a modern socratic dialogue between socrates and theaetetus presented in the "ordinary language." the discussion centers on self-Referring statements and their meaning. (staff).

Mi teoría de la democracia es muy simple y fácil de comprender para todos. Pero su problema fundamental es tan diferente del de la antigua teoría de la democracia, que todos dan por supuesta, que parece que esta diferencia no ha sido aprehendida, sólo por su simplicidad. Ella evita rimbombantes palabras abstractas como "regla" (rule), "libertad" y "razón". Creo en la libertad y la razón, pero no creo que uno pueda construir una teoría simple, práctica y provechosa en estos términos. (...) Ellos son demasiado abstractos y bastante aptos para ser usados mal, y, ciertamente, no se gana absolutamente nada definiéndolos. (shrink)