‘[I]t is more interesting to go on trying to solve problems than to look back on one’s failures’: these words we find in an incomplete one-page typescript, possibly intended to introduce Karl Popper’s own intellectual autobiography. Popper subsequently deleted these words and opted to introduce the history of his intellectual development with a section on his working experience under Adalbert Pösch–an old master cabinetmaker, the only master mentioned in the book–whose claims of omniscience taught him how little he knew, and that all he could ever aspire to was to realize the infinity of his ignorance. More than anyone else, Pösch made him realize his fallibility, and turned Popper into a disciple of Socrates, the first philosopher to embody the scientific attitude that emphasized criticism and self-criticism.
However, the very fact that Popper eventually deleted these words, as well as others, indicates that he was actually facing several problems. Indeed, Popper’s published work seems to obscure, rather than illuminate, the intellectual transformation that he underwent as a young intellectual. He helped the confusion both by omitting historical signposts from his works in the first place, and then reconstructing his intellectual autobiography in a manner that concealed most turns and dead ends. As an intellectual autobiography, his should be and is the history of his ideas, of how he worked his way from one philosophical problem to another. Little room is left for personal elements or the context in which ideas develop. Imposing his mature philosophy upon his memories, he transformed his intellectual development into a linear progress–from youth politics to psychology in the Twenties, to the logic of science in the Thirties, to his work on the open society in the years of World War II. Viewing science as an adventurous revolutionary project, an uneneded quest for ever growing but never certain knowledge, he undertook an autobiography in which a sort of rationality of scientific revolutions dominates the narrative, concealing the plurality of directions in which his thought developed, the diverse options, the intellectual impasses, and the decisive turning points.
Hacohen’s declared intention is to rectify the life that Popper himself distorted, calling on contexts that Popper ignored–above all, the ethos of the assimilated Jewish intelligentsia of Vienna of the time. His aim is not only to provide a fuller and more accurate account and to recover a rich culture that vanished (partly into exile, partly up Auschwitz’s chimneys), but also to rescue the young Popper for the present, to see how the adventurous progressive socialist who revolutionized the philosophy of science and formed a compelling vision of the open society can help us rethink our problems today, in the post-Cold War era.
Combining extensive study of the historical and cultural context, detailed archival research and engagement of Popper’s politics and philosophy, Hacohen’s book is a major contribution to the understanding of a central figure of twentieth century philosophy, both as a man and as a thinker. It traces the formation of Popper’s philosophy, providing a splendid account of the fin-de-siècle and interwar Viennese milieus. Most notably, he shows how the political and philosophical dilemmas of Vienna 1900 are still with us, and offers Popper’s solutions as an alternative to poststructuralists’ ones.
The book is not directed primarily to Popper’s followers. Nor does Hacohen want to redress the current political imbalance in the reception of Popper’s work. He openly takes exception to the uses to which the political right–in Austria, no less–has put Popper. In the late Sixties and early Seventies Popper actually became, on account of his critique of Marx and the confrontation with LSE students (secluded in Penn, Buckinghamshire, he never fully understood the events) the establishment philosopher par excellence–as his most recalcitrant pupil, Paul Feyerabend, described him: ‘the established Sir Karl of later years’. The purpose of the book is to reverse Popper’s absorption into right-wing discourse in the postwar years, and claim him for new progressive politics. Recovering the historical Popper, whether the committed young socialist or the old, more conservative Popper, who remained supportive of the welfare state, is certainly the best antidote to the political misappropriation of his work. Therefore, Hacohen intends primarily to address the academic left, that has been, in his view, ‘on the wrong track since it took the postructuralist turn in the late 1970s. I hope to convince them that Popper saw more clearly than they have through the philosophical and political problems preoccupying them and that he provides a more promising direction in the search for answers. In short, I hope that Popper can help the academic left set a new progressive liberal agenda that will seek to recoup the social losses of the last two decades’ (p. 2).
Popper would probably have objected to much of Hacohen’s work: he always did his best to control his public image and shape his reputation, fighting others’ efforts to reconstruct his intellectual history that did not fit his own reconstruction. Moreover, he always insisted–and rightly so, of course–that the origins of ideas have nothing to do with their validity: what counts is intersubjective criticism, not freedom from prejudices. Hacohen rightly claims to be extending his method, not challenging it: questions of genesis are not theoretically trivial, and are especially welcome when they encourage and facilitate criticism.
But for an ‘Epilogue’, briefly describing the postwar years, Hacohen stops his reconstruction in early 1946, when Popper and his wife arrived in Britain, with the Gombrichs waiting for them at the docks, presenting him with one of the first printed copies of The Open Society and Its Enemies. From Hacohen’s point of view, in his later years Popper certainly advanced new ideas, like the propensity interpretation of probability, evolutionary epistemology and World 3; also, his philosophy of science became more thoroughly nonfoundationist and antideterminist. But, whereas the young Popper was open to new influences, willing to adapt and change, the old Popper focused on developing an already established philosophy, the sources of innovation almost all internal.
This is questionable. Popper’s arguments on the topics of realism, indeterminism, propensities, World 3, mind and self, constitute a distinctive metaphysical phase in his thought–beginning in the Fifities, about twenty years after the ‘philosophical breakthrough’ described by Hacohen, and developed in close co-operation with Joseph Agassi (and John Watkins). Epistemological and methodological matters, together with political and ethical concerns, are now considered within the context of the problem of cosmology, which Popper draws from the Presocratics: ‘the problem of understanding the world–including ourselves, and our knowledge, as part of the world’.
Hacohen suggests that it is the politics and intellectual engagement of the young Popper that is most relevant today, and it alone can shed light upon the formation of the philosophy that flourished in postwar years. As he did in his PhD dissertation (The Making of the Open Society, 1993), Hacohen primarily focuses on Popper’s two basic texts of his political philosophy, The Open Society and Its Enemies and The Poverty of Historicism, showing how they make little sense when read in the cold war context, due to the disjunction between the German-Austrian milieu, in which they were formed, and the Anglo-Saxon world, where they became popular after World War II. It was Red Vienna, not Soviet communism, that provided the grounds for his critique of Marx. When writing The Open Society and Its Enemies, he thought fascism reflected a primeval urge to return to the closed ‘tribal’ society, and Marxist mistakes prevented the working class from resisting effectively the fascist assault on democracy.
Let me focus here on what I take to be the crucial years for Popper’s intellectual development: 1929-1934. In his 1929 thesis on axiomatics in geometry (Axiome, Definitionen und Postulate der Geometrie), he first formulated the problem of scientific rationality and turned from cognitive psychology to methodology. These were his first steps into the Vienna Circle’s orbit: he read avidly the Circle’s works as they were coming out, and soon realized that his deductivism provided a corrective to the Circle’s views. Therefore, he sought to develop it into an alternative. He formulated the problem of induction and made it the centre of his critique of logical positivism. The Circle, he argued, failed to solve the problem; his deductivism succeeded. In 1930-1932, working on Die beiden Grundprobleme der Erkenntnistheorie, he discovered demarcation: induction dissolved into demarcation, thus shifting the focus of Popper’s revolution. As falsifiability moved from margins to the centre, the hypothetical character of science became evident. Returning to the foundation debate in the Fries-Nelson tradition, he extensively rewrote his earlier critique of Kant and Fries, formulating a new vision of science as ‘a deductive science that was empirical but not inductive, testable and confirmable but not certain, demarcated from metaphysics by falsifiability but not deeming metaphysics meaningless. Science left space for epistemology, methodology, and “non-scientific” philosophy’ (p. 199).
Critical dialogue with logical positivism propelled Popper’s revolution from the beginning. He used to work in virtual isolation, withdrawing into seclusion for lengthy periods, then reappeared to confront the Circle with new ideas. Circle members were, at intervals, a source of critical feedback that led him to crucial developments. He did not accept their challenges but, rather, worked out innovative responses. Though they were a crucial context for his philosophy, Popper’s differences with the Circle were significant. Hacohen takes exception to those historians who have tended to accept the Circle’s contention that Popper exaggerated his disagreements with positivism. Popper’s critique sprang from a marginal Kantian perspective foreign to logical positivism. The movement regarded it as a contribution to their own scientific philosophy. He vainly protested, insisting that his critique was deadly. The movement failed to grasp the fundamental difference between decision and justification, thus never recognizing the significance of Popper’s critique–as the persisting ‘official’ history of the demise of the movement still testifies. According to this stereotypical history, Popper was a minor logical positivist who introduced falsifiability as a criterion of meaning and exaggerated his difference from Carnap and from Neurath. As Hacohen clearly shows, this is a convenient history, which rests on an emphasis on certain aspects and criticisms of logical positivism at the expense of an oversight of other aspects. The demise of logical positivism never took place; but a deadly criticism of it was offered already in the early Thirties by Popper.
Surely, his relationship to the movement was problematic: he developed his philosophy in dialogue with theirs, but he refused to take the linguistic turn: ‘he understood it perfectly, but, rather than take the turn, he found a way to cross the junction, forging his way straight ahead’ (p. 209). He admired the early work of Schlick, and took courses under him; he studied Wittgenstein, Hahn and Carnap, also visiting the latter’s seminars, but he was no logical positivist. Therefore, he can not be placed within the spectrum of opinions on various issues in the Circle–since that would amount to an oversight of the different problem situations underlying the disagreements. Popper upheld Kant against Wittgenstein and the Vienna Circle: even though Kant did not have the right answers, he was on the right track to discover better ones, whereas the attack on Western metaphysics manifested old philosophical absolutism and would lead to a dead-end. He pursued a reform of metaphysics, not its overthrow. He regarded himself as an heterodox Kantian, and the positivists as precritical. He was developing an alternative to positivism, seeking to redirect the philosophy of science away from language to problems.
Nonetheless, collaboration between Popper and the Circle did take place. Most Circle members proved remarkably receptive to their critic: practicing the intellectual openness that Popper only preached, the Circle gave him the chance to develop and articulate the most compelling philosophy emerging from the interwar Viennese milieu. In this sense, Popper was the true heir of the Vienna Circle’s legacy. Both he and they reformulated and reinforced their positions in response to mutual criticism. Two philosophies were in dialogue. The Circle denied that there were two, and some of its official heirs still do. Popper, they claimed, belonged to their movement. Not so. Mutual misunderstandings, Popper’s exile to New Zealand and the delay with which his books were eventually published (The Logic of Scientific Discovery, the English translation of Logik der Forschung, saw the light in 1959, while Die beiden Grundprobleme appeared only twenty years later, and it has not yet been translated into English) created a distortion of Popper’s philosophy for the next generation. The ‘legend’ of a positivist Popper had emerged.
The philosophical breakthrough of 1930-1932 was completed in the following two years with Logik der Forschung (which got published in November 1934): after drawing a new vision of science and philosophy, Popper developed an innovative methodology to support his vision, applying it to probability and quantum physics. Die beiden Grundprobleme analyzed the correspondence between epistemology and scientific practice. Logik completed the shift: setting the rules of science, methodology is prescriptive, not descriptive; induction, whether used in practice or not, is invalid. Popper’s demarcation was better than that advanced by the Circle’s members not just because it corresponded to scientific practice, but also because it clarified and resolved its problems.
Taking Fries’s and Nelson’s demonstration of endless regress in epistemology as a point of departure, Popper nonetheless defended epistemology, though without attempts at grounding knowledge: epistemology’s task was not to justify statements, but to investigate methods and criticize procedures, pointing out contradictions and misappropriations. It sought to clarify, criticize and improve practice, not to ground it.
Faced with Fries’s trilemma–dogmatism, infinite regress, or psychologism–he gave up the idea that justification is a necessary condition for scientific knowledge: our scientific knowledge can not and need not be justified. His was a revolutionary solution. Testing had no natural end point; a decision to stop and accept a statement was conventional, and such an acceptance was dogmatic, in a sense, but it was an undangerous dogmatism: when doubts emerged, scientists renewed testing. Subjective convictions contributed to the consensus that ended testing–but, again, this was harmless: scientists did not ground statements, and though they accepted them in accordance with an objective methodological rule, stipulating admission of confirmed test statements into science, these rules were not so strict as to impose unique moves in all situations, and allowed for moves that led to the upholding of errors. ‘Dogmatism, endless regress, and psychologism all played roles in scientific work, but they were rendered innocuous by science’s hypothetical, falsifiable character’ (p. 230). Science progressed not by discovering unshakable truths, but by eliminating errors: change was its hallmark, and intersubjectivity (that is, Kant’s surrogate for objectivity) was the sole basic rule. And though it was no guarantor of progress, it was what kept the scientific enterprise continue to progress thus far. As long as science progresses, research may continue. Convention and experience modified, rather than determined, each other. Corroboration was an assessment of how well a theory stood up to tests: it represented a rough estimate that had no truth value or probability value. Theory informed all action and decision, and decision can not be justified. Tarski enabled Popper to speak about correspondence of a statement and a ‘fact’ in one language, thus relegitimizing ‘commonsense’ truth. Experience and access to reality remained problematic, but it was possible to learn from it all the same. There was no way of knowing for sure what the facts were, and whether a statement actually corresponded to them. Truth (i.e. correspondence) was an ideal, a regulative idea, always sought and never sure to have obtained: indeed, we may well obtain truth, but not justified certainty that we have obtained it. The linguistic turn no longer threatened realist metaphysics and objective science. Rationality required no foundation, only critical dialogue: it was the end of foundationist philosophy.
While Popper was accomplishing his methodological revolution, prolonged tensions within the Circle broke into the open with the ‘protocol sentences debate’ in the pages of Erkenntnis (1934, summer and fall issues). Popper was initially oblivious to the debate. Neurath eventually directed him to the exchange, which provided him with new ammunition for his attack on positivist psychologism and subjectivism. Taking issue with the literature re-evaluating Otto Neurath and his legacy, Hacohen sheds new light on the relationship between Popper and Neurath, and also expresses his discontent with the current state of the debate on interwar Viennese philosophy of science. In his discussion of the Popper-Neurath exchange Hacohen illustrates his views on the role and task of the historian’s work, as well as on the lesson to be learned from his account: ‘if the past is to inform rather then vindicate the present, its alterity must be preserved’ (p. 262).
Neurath’s review of Logik brought out the sharp contrast between protocols and falsification, the positivist-physicalist and critical Kantian programmes for philosophical reform. Though Carnap and Schlick were convinced that Popper was of their own persuasion (and Popper feared that Carnap’s ‘official’ favourable review of Logik, once again assimilating him into positivism, would have diminished his revolutionary contribution), Neurath disagreed. To him, alone among the Circle, Popper was positivism’s nemesis, the Circle’s ‘official opposition’. He clashed with Popper in the Paris and Copenhagen congresses, in 1935 and 1936. Then Popper went to his New Zealand exile, and virtually disappeared, out of touch and influence. Neurath, however, did not relent, fighting the legend of a ‘positivist Popper’ till his premature death in London, in 1945, left the legend contrasted by Popper alone in the postwar years.
Neurath shared with Popper a wide range of assumptions: with him, Neurath was epistemologically closer than any other Circle member. Both insisted that language could not be compared with reality and sought a way to bridge the gap between experience and language, so that experience informed scientific theory; both believed that observations are theory-laden and regarded them as provisional. Popper kept science and reality separate, yet allowing experience to arbitrate theoretical questions through a decision, logically and methodologically informed, to accept a falsifying statement. By contrast, Neurath’s linguistic protocols proved ineffective: hostage of the prison house of language, his attempt to translate psychological behaviour into physicalist language (as Carnap did) reached nowhere. Metaphysical disagreement underlaid the Neurath-Popper exchange.
Missing the nonfoundationism of his philosophy, scholars accord Popper a rough treatment. Those sharing his views have been unsuccessful in defending him because they are unwilling to engage poststructuralism (and some of those who do, like Noretta Koertge, end up defending scientific rationality in a manner that Popper could have found objectionable). In a new way, focusing on the foundation and protocol sentences debates of the mid-Thirties, Hacohen shows how ‘Popper provided the most viable response to “poststructuralist” dilemmas among the disputants: a modified conventionalist, nonfoundationist philosophy that safeguarded rationalism, but skirted the dangers of absolutism’ (p. 263).
In his later years, Popper spoke nostalgically of Habsburg (and classical Athenian) multiculturalism, praising culture clash as productive of great intellectual advances. In his view, culture clash allowed for critical dialogue, that transformed identities, transgressed boundaries and changed communities. But, Hacohen argues, ‘Popper underestimated the difficulty of creating a situation that would make such a dialogue possible. Culture clash under conditions of unequal power does not always create dialogue, or advance cosmopolitanism. It may result in oppression’ (p. 541). To him, Popper’s irrational commitment to rationalism, which constitutes his precondition to dialogue, is insufficient, since for an ideal speech situation power must be neutralized, so that it has minimal influence on dialogue: ‘socially disadvantaged groups do not have a fair chance of being heard, let alone prevail, in the so-called democratic political process’ (p. 543). It is difficult to reason over differences, he continues, especially ethnic and religious ones. The culture of debate, promoted by Popper in his seminars and writings, is ill suited to intercultural and political dialogue. ‘Participants in debate must recognize others as equal, make a genuine effort to listen, understand, and learn, and attempt to reach agreement and compromise. […] Only in a deliberative democracy (or the Open Society) are intersubjective criticism and politics proximate. We do not yet live in such a democracy, and if we ever come close, there will be communities that do not accept intersubjective criticism’ (p. 545). In other words, though liberal communicative ideals and Popper’s rationality criterion tell us where we should head, they provide no guidelines for evaluating political proposals. ‘If critical rationalism is to remain politically vital, not merely a regulative ideal for a utopian cosmopolitan age, Popperians need to develop guidelines for political evaluation’ (p. 546).
Hacohen makes a point here, challenging all Popperians to a rejoinder (and I take myself to be one). He is right: Popper did not suggest how we might proceed in situations that do not allow for an open dialogue and admit of intersubjective criticism. But did Popper promise to solve a problem here that he did not? As a matter of fact, it is precisely looking back to Popper’s youth years, through the very new spectacles Hacohen’s impressive reconstruction provides us with now, that we understand the true conditio sine qua non of his lifelong intellectual quest.
A radical choice is the origin of the whole of Popper’s philosophy–a decision exemplified best in an early encounter with a Nazi youth, who refused to argue and said Popper: ‘What, you want to argue? I don’t argue: I shoot!’. He was confronted with an alternative, and built the entire edifice of his philosophy on the decision to choose for dialogue, to fight with words instead of swords, to let our theories die in our stead. Of course, this marks a difference between the rules obtaining in the ideal scientific and political communities: philosophers and scientists can (and actually must) experiment with ideas, while politics should not likewise experiment with human lives. Still, critical rationalism identifies with Popper’s humanism, since rationality is not so much a property of knowledge as a task for humans. According to Popper, rationality is inscribed within the framework of a more basic and general rationality, the rationality of the world and of the human person. Popper sees the rational attitude as a moral obligation against scientific dogmatism and irrationalism, and as a clear option against violence. It is an attitude of dialogue, accepted with the full awareness of the difficulty of such a task.
It is, of course, an expression of faith–a faith in peace, humanity, freedom and intellectual modesty, and in the possibilities of critical discussion: it is an appeal to reason, and ‘reason also is choice’, as John Milton put it. William Bartley tried to show that such an irrational commitment was unnecessary, an unnecessary concession to irrationalism: if someone does not want to engage in a dialogue and shoot, then there is anyway nothing, of course, Popper (or others) can do about it. And, as Bartley added, Popper was still not ready to propose a fully non-justificationist agenda, as he should. Popper did acknowledge that Bartley alerted him to the extent of his non-justificationism and to the fact that this was the aspect of his philosophy that made his logical-positivist peers so hard to take his ideas as seriously as they deserve. However, it is precisely such an irrational commitment that gave rise to Popper’s philosophy. To him, dialogue was a value. All life is problem solving: problems arise together with life, and there are problems only when there are values. When violence wins over peaceful debate, reason must give in. As Popper said in his later years, ‘we should not shrink from waging war for peace’: we have to fight to establish the minimal conditions for critical exchange. Toleration allows differences to exist; respect means willingness to learn from them. Toleration and respect are obligatory, not criticism. We do not have to try to make people critically minded: we have no right to force them to offer or accept criticism, nor to learn to participate effectively in the game of critical discussion. It is in their right to refuse to do so. All we can (and have to) do is to try to help them become critically minded if and when they request that. Following the road of reasonableness and taking other people seriously, i.e. respecting their freedom, is far more important than persuading them. Popper’s methodological proposals reflect both hope that rational debate will lead to improvement, and the conviction that criticism entails responsibility. Such responsibility can be encouraged, but not forced.
The problem of rationality is the most important of philosophical problems and, in a sense, the core of philosophy itself. It concerns the choice of one’s principles and values, says Popper. As Joseph Agassi put it, it concerns the choice of one’s lifestyle. The solution to the problem of rationality is the very starting point of every philosophical approach, the very choice of one’s lifestyle. Popper’s approach to philosophy is his solution to the problem of rationality. His life is the very embodiment of his understanding of rationality and his solution to its fundamental problem.
In Popper’s view there are two natural coalitions: between determinism and inductivism, on the one hand, and between indeterminism and fallibilism, on the other. He clearly chooses the latter. As John Watkins noticed, in the closing lines of his contribution to the two volumes on The Philosophy of Karl Popper, ‘learning about the world means, on the first view, being conditioned by it; on the second view, it means adventuring within it’. It is not simply an intellectual affair or a matter of taste: without the possibility of self-governing, life and the quest for knowledge would be nothing but farces. Popper believed in an ‘open universe’ and theorized that, in science as well as in politics, free and responsible choice is a moral decision. This makes the balance achieved by Popper’s thought unsteady–but unsteadiness is the condition for life. Firmly committed to hard work, he spent his whole life struggling with problems, failing as often as succeeding. His was the intellectual quest of a twentieth century Sysiphus–a Sysiphus who, unlike that described by Albert Camus, in the unending struggle with problems and not condemned to repetition, managed to be happy, achieving progress till the end.
 Fragments of the Autobiography, Karl Popper Archives (134,34).
 Paul K. Feyerabend, Science in a Free Society, London: New Left Books, 1978, p. 115.
 All page references are to Hacohen (2000).
 Karl R. Popper, ‘Preface to the English Edition, 1958’ to The Logic of Scientific Discovery (London: Hutchinson, 1959), p. 15; see also the three volumes of the Postscript, in particular The Open Universe. An Argument for Indeterminism (London: Hutchinson, 1982), chapter IV and ‘Addendum 1’; and Quantum Theory and the Schism in Physics (London: Hutchinson, 1982), p. 1 and chapter IV.
 Denying all that amounts to a distortion of history for political purposes, not to a rational reconstruction offered for intellectual ones: see my review of Michael Friedman, Reconsidering Logical Positivism (Cambridge: Cambridge University Press, 1999), Newsletter of The History of Philosophy of Science (HOPOS) Working Group, vol. 5, no. 2, spring-summer 2000, pp. 18-19. It is not simply a matter of priority. It is a matter of intellectual honesty. We might like or dislike Popper’s philosophy but, as scholars, philosophers or historians, we would better confront his ideas: the best way to express disagreement is not ignoring ideas, but criticizing them–as most of Popper’s closer pupils and disciples did.
 Neurath’s interpreters believe that the charge of psychologism is a distortion by Popper. I find their arguments unconvincing, and Hacohen himself thinks they are problematic.
 Karl R. Popper, The Myth of the Framework. In Defence of Science and Rationality, London and New York: Routledge, 1994, p. XIII.
 John Milton, Paradise Lost, 1674, Book III, 108.
 As Hacohen remarks, ‘Bartley wisely disposed of the justificationist ladder once he had seen the world aright’ (p. 519). See also my ‘The Ethical Nature of Karl Popper’s Solution to the Problem of Rationality’, Philosophy of the Social Sciences, 2001, in press.
 Karl R. Popper, All Life is Problem Solving, London and New York: Routledge, 1999, p. 119.
 John W. N. Watkins, ‘The Unity of Popper’s Thought’, in Paul A. Schilpp (ed.), The Philosophy of Karl Popper, La Salle, Illinois: Open Court, 1974, pp. 371-412; the quotation is from p. 407.