2. The Vienna Circle

Popper's intellectual and social connections to the Vienna Circle were complicated and this makes interpreting his early thought notoriously difficult. This section demonstrates that Popper's early thought incorporated Kantian elements from the Vienna Circle as well as some non-Kantian positions that Popper received through intellectuals of the Lvov-Warsaw School. Nonetheless, Popper disagreed on many of the central premises held by the Vienna School ‘neo-positivists’.Footnote ¹ Possibly as a result he was never privileged with a personal invitation to attend Schlick's seminar, thus was never officially a member.Footnote ² Popper was not, as Leszek Kołakowski (1927–2009) described, one of the most prominent members of the Vienna Circle,Footnote ³ nor was he a logical positivist as Feyerabend stated.Footnote ⁴ Despite this, his writings and actions were seen to directly contribute to the reputation of the Circle. It is out of this complex social and intellectual environment that much of the confusion concerning Popper's positivism arises.

It was largely through the work of Otto Neurath (1882–1945) that the group of Viennese analytical philosophers known as the Vienna Circle achieved fame, especially through Neurath's journal Erkenntnis.Footnote ⁵ The Vienna Circle has tended to be seen as a homogenous group devoted to an oversimplified and naïve focus upon Russellian and Wittgesteinian logical positivistic doctrines, and Popper's public writings did not help the problem of this misconception surrounding the Vienna Circle. He perceived that his reputation abroad during the years in New Zealand (1937–1945), in which he wrote The Open Society (1945), and after would hinge upon his association with the Circle. Subsequently, Popper relied heavily upon the endorsements and testimonies of the members of the Circle in the years before taking the post at the London School of Economics in 1946 and did much to sustain his seminal influence in the Circle. This can be seen in Unended Quest (1974) in which Popper claimed responsibility for killing logical positivism and sealing the Circle's fate.Footnote ⁶

However, through Popper's private correspondence we get a remarkably different picture of his relationship to the members of the Circle. As the Vienna Circle constituted the pre-eminent philosophical school in Austria, Popper was invariably drawn towards them. He formed life-long intellectual relationships as well as close friendships with members of this group. If he were to build an international reputation, Popper knew it could be done through this group. In Unended Quest Popper gave as one of his reasons for writing Logik der Forschung (1934) a desire to travel abroad due to a feeling that central Europe would once again be plunged into another catastrophe.Footnote ⁷ Thus, Popper built his career around the Vienna Circle and relied heavily on the recommendations of its members in building his international reputation and securing employment abroad. The letters of correspondence between Popper and Rudolf Carnap (1891–1970) from 1940 to 1950 help to break down certain naïve myths of the Vienna Circle intended for public consumption that Neurath, the ideologue of the Circle, for political reasons and Popper for professional reasons helped to create.Footnote ⁸ Despite their technical philosophical differences, Popper and Carnap continued to work on similar scientific problems such as probability as well as concerning themselves with similar ethical and political debates. The letters between Popper and Carnap reveal a congenial and collaborative friendship of two remarkably similar scholars both imbued with the thought of Kant. Carnap stated in one of his letters that he believed that his views in questions of semantics largely agreed with Popper's.Footnote ⁹

Politically the two held similar positions in relation to the problematic reception and understanding of Hayek's thought in the U.S.A. Both felt that aspects of his thought opposing unrestricted capitalism had been neglected.Footnote ¹⁰ Carnap also felt the need to criticise Marx carefully in order: ‘not to furnish arguments to those who not only differ with his views but also reject his goal’.Footnote ¹¹ From these letters we get a sense of the common concerns over political and social problems that united Popper with Carnap. We can also see that Carnap was ready to provide advice and criticism of Popper's political arguments. Within the breadth of intellectual concerns that characterised the thought of members of the Vienna Circle it is clear that Popper's thought has its rightful place, however defining such a place has been a matter of considerable scholarly debate.Footnote ¹²

David Frisby also locates Popper's thought within the positivist camp of the Vienna Circle however, he also hints at an alternative locating of Popper's thought within a neo-Kantian camp. Frisby stated that the analytical theory of science associated with logical positivism moved beyond its radical phase into two separate yet sometimes overlapping directions. The first direction concerned the logical reconstruction of scientific languages and the second with the logico-methodological reconstruction of the research process itself.Footnote ¹³ The former tradition Frisby associates with Carnap's work which led to what became known as ordinary language philosophy. The latter, Frisby associates with Popper's concept of falsificationism. Frisby then states that Popper broadened his theory of scientific method to incorporate the social and political world.Footnote ¹⁴

At this point it is important not to oppose the Vienna Circle to the neo-Kantians. Rather it is the case that Popper's thought reflects the complexity of the Viennese intellectual environment in which the two trajectories along which logical positivism developed were themselves due to a broader neo-Kantian inheritance. Frisby makes indications towards this complex inheritance by stating that the neo-Kantian conception of science ‘reduces science to methodology in such a way that what characterizes science is its methodology in the abstract’.Footnote ¹⁵ This is stated to be the position of both the South West School and the Marburg School, both of which isolated methodology from its object in the development of their approaches to science.Footnote ¹⁶ Thus we see two neo-Kantian positions underpinning an aspect of neo-positivism that Popper's thought was seen to characterise. This separation of a central feature of the Vienna Circle from the logical-empiricism of Wittgenstein raises problems for our understanding of the ‘neo-positive’ nature of the Circle in general. In this regard it is safer to understand Popper's thought as resulting from a neo-Kantian tradition to a greater extent than a neo-positivist one.

Popper's understanding of science is remarkably neo-Kantian and reflects aspects of both the South-West School and the Marburg School. Windelband (1848–1915) of the South-West School made the distinction between a science generating laws from a science of individual events: the former are considered to be nomothetic and the later to be idiographic.Footnote ¹⁷ Popper's understanding of science is a modification of the nomothetic understanding which holds laws as existing in nature and it is our task to discover them through the generation of hypotheses which aim at a high degree of ‘verisimilitude’ or likeness to the truth. However, it is to the Marburg School of Hermann Cohen (1842–1918) and Paul Natorp (1854–1924) to which we must turn to appreciate the greatest debt that Popper owed to neo-Kantian science. The Marburg School was primarily interested in scientific knowledge and took scientific cognition to be the prototype of all cognition. For them, epistemology was the analysis of the logical foundations (or in Popper's case lack thereof) of the exact sciences. Frisby suggests that in some respect modern positivism has its roots in this tradition.Footnote ¹⁸ If this is the case, then Popper had a unique advantage over the other members of the Vienna Circle as his early education was directly influenced by Marburg School cognitive theory through the cognitive psychology being conducted by the Würzburg School of which Popper's supervisor Karl Bühler was a member.

A different picture is drawn by Friedrich Stadler who argued that viewed from a greater distance Popper's work can be seen to be closer to that of the Vienna Circle than Popper himself cared to admit, and that the Vienna Circle members themselves would not have perceived such a great separation between themselves and Popper.Footnote ¹⁹ Stadler has shown that Popper, despite his intellectual disagreements, was on good terms with its members many of whom he met with regularly.Footnote ²⁰ The similarity of Popper's thought with that emanating from the Vienna Circle can be supported from a number of different standpoints. However, the most important theoretical similarities between the two do not pertain to the unique features of the Vienna Circle's logical positivism and language philosophy, but are the result of the shared Kantian epistemological mindset found in both Popper and the early works of the members of the Circle such as Schlick and Carnap. However, recent work on the Vienna Circle supports the need to appreciate the fundamentally Kantian mindset that underpinned the way its members approached the philosophy of science and which influenced the broader conceptual distinctions that they formed.Footnote ²¹ According to Friedman in Foundations of Space-Time Theories (1983), the Vienna Circle itself started as a neo-Kantian movement whose observational-theoretical distinction was actually a continuation of the Kantian form-content distinction; as a result much of the Circle's philosophy of science remained ‘indirectly Kantian’.Footnote ²²

Despite the similar problem situations and neo-Kantian undercurrents that united Popper with the Vienna Circle, his work nonetheless contains many different technical features to that of the Circle's other members. To appreciate the scientific methodological and epistemological points of divergence between Popper and the Vienna Circle, it is fruitful to compare Popper's work with that of another central European school of analytical philosophy, namely the Lvov-Warsaw School. Through the use of Alfred Tarski's (1901–1983) work as well as that of other members of the Lvov-Warsaw School, Popper used one tradition of analytical philosophy to counter the arguments of the Viennese analytical philosophers such as, Carnap, Schlick and Reichenbach, as well as Wittgenstein in Cambridge. However, as Burdman-Feferman and Feferman have shown the members of the Vienna Circle themselves, particularly Carnap, were directly influenced by Tarski and through him were influenced by the other prominent figures of the Lvov-Warsaw School.Footnote ²³

However, Popper was also familiar with the writings of other members of this school and his personal library contained books both in English and in Polish by the figures of this school.Footnote ²⁴ Popper's understanding of rationality has closer affinities with the anti-irrationalism of one of the school's leading thinkers Kazimierz Ajdukiewicz (1890–1963) than with any of the Viennese ‘positivists’. For Ajdukiewicz, every rationally accepted proposition ought to be inter-subjectively communicable and testable. This emphasis upon the link between standards of rationality, testability and inter-subjective requirements for objectivity reflect the central pillars of Popper's critical rationalist methodology.Footnote ²⁵

More broadly, Popper's methodological approach to analytical philosophy can also be seen to be closer to the Lvov-Warsaw School than to the Vienna Circle. In opposition to Wittgenstein and his influence upon the Vienna Circle, Popper much like the Lvov-Warsaw School, saw the task of analytical philosophy as not primarily concerned with linguistic analysis. Popper (at least after the Logik) in accordance with Kazimierz Twardowski (1866–1938), the School's founder, saw that philosophy should concern itself with problems rather than distinguishing between different modes of ‘good’ (scientific) and ‘bad’ (metaphysical) knowledge.Footnote ²⁶ Although Popper made such a distinction in his falsificationist methodology, reflecting the concerns that he shared with the Vienna Circle (a methodological formalism which to Popper's detriment he could never overcome and which Feyerabend strongly criticised),Footnote ²⁷ he nonetheless saw the need to solve concrete problems as being a more fundamental concern.Footnote ²⁸ As metaphysics was believed to play a part in problem solving then it could not be abandoned by Popper; however, it must be regulated by reason and guided by our background store of conjectural knowledge. In this way Popper's dissent from the anti-metaphysical insistence of Wittgenstein's linguistified Kantianism and finitism, that was shared in variable measure by the logical positivists of the Vienna Circle, reflected the standpoint of another leading member of the Lvov-Warsaw school, namely Tadeusz Kotarbiński (1886–1981). Kotarbiński saw the metaphysical discipline of ontology, as being indispensable for philosophical inquiry.Footnote ²⁹ For Popper, metaphysics was intrinsic to science, insofar as explanatory theories transcend experience. Metaphysics is unavoidable as every ‘fact’ for Popper contains ‘universals’ which entail ‘law-like’ behaviour.Footnote ³⁰ However, accepting that metaphysics is intrinsic to science and not something in opposition to it then Popper in his mature post-Logik thought, from a broad philosophical perspective can be seen to accept what Victor Kraft (1880–1975) believed to be the common tenet of the Vienna Circle: ‘that philosophy ought to be scientific’.Footnote ³¹ It is only in regards to this broad tenet that Popper can be regarded as being philosophically akin to the Vienna Circle, as his acceptance of metaphysics and rejection of logical positivism meant that he did not conform whole-heartedly to the Circle's epistemological or methodological views.

Popper's anti-positivist analytical approach to philosophy took time to develop, although metaphysical speculation was a characteristic of his earliest philosophising.Footnote ³² The elements for Popper's later realist and objectivist interpretations of scientific theories can be seen from his earliest works. Popper would not develop his realist and objectivist theories to their full and mature extent until after the Logik when he was able to change his opinions on the rational arguability of non-falsifiable theories which coincided with a practical appreciation of the benefits of transcendental criticism.Footnote ³³ Popper's early thesis ‘Gewohnheit’ und ‘Gesetzerlebnis’ in der Erziehung (1927) written for the Pedagogic Institute, reveals that although he was studying under Karl Bühler in a markedly Kantian and anti-positivistic environment, the lure of neo-positivism was great and he was not yet in a position to theoretically combat it.Footnote ³⁴

In this 1927 thesis it is stated: ‘Although this work is highly theoretical in its main parts, it is nevertheless the result of practical experience and shall in the end come to be used in practice. Its method is therefore largely inductive.’Footnote ³⁵ This work as a whole is a rather unusual piece, in which inductivism is quite naturally given as the obvious choice of method. As his thesis progresses the types of evidence used to support his psychological arguments concerning the fear of the known and angst for the unknown include Kierkegaard,Footnote ³⁶ Nietzsche,Footnote ³⁷ Dostoyevski,Footnote ³⁸ and Shakespeare,Footnote ³⁹ alongside the expected Würzburg School psychologists and Kant. It is a remarkably un-Popperian work indeed, if we were to misunderstand Popper as one of Kołakowski's positivists. It is apparent that this thesis reflects his early and broad philosophical interests and his early attempt to bring his thought into line with the restrictive inductivist methodology of the Vienna Circle and the scientific concerns of the Würzburg School.

Only a year later, however, we can begin to see the beginnings of a Popperian philosophy and a system of thought, based upon arguments which would be developed throughout his life. This is first clearly evident with his 1928 dissertation Zur Methodenfrage der Denkpsychologie. In this work, Popper develops Bühler's attempt in Die Krise der Psychologie (1927) to reform psychology through the ‘die Axiome der Sprachtheorie zu finden’.Footnote ⁴⁰ As Bühler's book was only published in 1927, it indicates that the shift from Popper's unusual 1927 inductive thesis to the first real Popperian work in 1928 may be owing to a greater familiarisation with Bühler's work. Thus, one can speculate that Bühler's Die Krise der Psychologie, may have been a significant, but by no means only, source of Popper's opposition to the Vienna Circle's inductivism and neo-positivism. It was through this book that Popper's earlier leanings towards Kant in his 1927 thesis could be systematically validated for a methodological program. Bühler's 1927 book reflects Popper's similar concerns with a biological (biologischer) factor underpinning methodology.Footnote ⁴¹ Further, as a result of the impact of a biologically oriented theory of communication, a methodology that is built upon this for Popper would have to be deductive and have a transcendental component.Footnote ⁴² Popper would later extend these features that were originally developed by Bühler from what was then the cutting edge science of Denkspsychologie or cognitive psychology to scientific work as a whole. An attempt was made by Popper to explain this argument for the deductive and metaphysical basis behind all of our knowledge in a letter to Victor Kraft (1880–1975) of the Vienna Circle in 1967.Footnote ⁴³ From this letter it can be seen how Bühler's work in finding a linguistic solution to the problem of method in psychology remained the feature at the centre of Popper's philosophy throughout his later years. Arne Petersen has suggested that the real breakthrough came in 1929 with Axiome, Definitionen and Postulate der Geometrie where Popper realised that logic rather than psychology, was of fundamental concern for scientific discovery.Footnote ⁴⁴ This early development from psychological to biological then to logical concerns in Popper's approach to methodological problems is an important feature of his early thought.

Ultimately, Popper's movement away from the positivist influences of the Vienna Circle can be seen to be part of a broader trajectory away from logical positivism within the Circle itself, partly resulting from an increasing interaction with the ideas of the Lvov-Warsaw School. In Unended Quest Popper famously responded to the question of who killed logical positivism with a feigned confession: ‘I fear that I must admit responsibility.’Footnote ⁴⁵ The logical positivists themselves never accepted Popper's infamous assertion. Artur Rojszczak cites a letter from Tarski to Neurath from 1936 in which Tarski stated: ‘And now Carnap was of the opinion, that just the liberation from this hindering influence of W.[ittgenstein] is due to the Varsovians…’.Footnote ⁴⁶ Among the various reasons for the abandonment of the early Wittgenstein and failure of logical positivism in Vienna it seems that Tarski's lectures in Vienna and the discussion which they provoked bear a measure of responsibility.Footnote ⁴⁷ However, further on in Unended Quest, Popper made another assessment of the demise of the Vienna Circle that is often overshadowed by his more ostentatious confession cited above. In opposition to Popper's claim to have killed logical positivism he stated:

This criticism of the ‘scholasticism’ into which the Vienna Circle degenerated would become a reoccurring criticism that Popper would level against academic philosophers later in life. Such a fear of ‘scholasticism’ or the abstraction of the concerns of philosophers from the real problems facing humanity would become a characteristic ideal of Popper's critical rationalism. Popper perceived Russell's vision of the philosophy of science as ‘providing a possible cure for the diseases of the modern world’, as losing its focus in the twentieth century, which was in no small part due to the cult-like influence of Wittgenstein.Footnote ⁴⁹

3. Julius Kraft: an Extraordinary Friendship

I contend that Popper's most important philosophical influence was his close friend Julius Kraft (1898–1960). According to David Miller, Popper had many informal conversations with Kraft during 1924–1925.Footnote ⁵⁰ Popper wrote that at the time in which he met Kraft he had been studying philosophy for some years without actually having contact with a teacher of philosophy or anybody with knowledge of the subject in any depth.Footnote ⁵¹ Popper stated that Kraft was a ‘wonderful teacher’ and that they discussed problems for hours, for days and nights.Footnote ⁵² Kraft was clearly the more proficient philosopher of the two during the years following the First World War in Vienna, at least in terms of qualifications and publications. The extent to which Popper not only shared philosophical positions and problems with him, but also deeper philosophical attitudes and interests, indicates the centrality of Kraft for Popper's intellectual development. It was Kraft who Popper stated ‘never ceased to study, and to ponder about, Kant's three Critiques, especially the first. Kant's resolution of the antinomies – his “transcendental idealism”’.Footnote ⁵³ As Popper understood it, for Kraft, Kantian critical rationalism meant that all reasoning is discursive rather than intuitive as Kant stipulated that there is no such thing as an ‘intellectual intuition’ which is an ‘authentic source of knowledge’, in the sense that what is intellectually intuited is true. For Kraft, ‘the intuitionist philosopher is an authoritarian philosopher’.Footnote ⁵⁴ Kraft's arguments against intuitionism in Von Husserl zu Heidegger (1932 [1957]) would become a central feature of Popper's philosophy and would significantly influence Popper's negative attitude towards Heidegger.Footnote ⁵⁵ This belief in the discursive character of human reason would become one of Popper's fundamental beliefs and is the basis for his philosophical concern of the particular needs of rational argumentation in relation to the complexity of intellectual and social problems that we face.

Hacohen stated that Kraft's Von Husserl zu Heidegger in which he attacked phenomenology, existentialism and Hegelianism, as well as Kraft's Die Unmöglichkeit der Geisteswissenschaft (1934) almost read as sequels to The Open Society.Footnote ⁵⁶ Kraft's works significantly predate the publication of Popper's major social and political works and reflect Kraft's pivotal role within the Fries-Nelson critical rationalist tradition. As such, Kraft's works ought not to be seen as sequels but more appropriately, as having a greater significance in foreshadowing The Open Society than Popper himself acknowledged. A reassessment of Popper's positions in relation to the works of his ‘teacher’ and ‘friend’ Kraft would be a valuable exercise in order to better understand Popper's originality. Such an exercise would also bring to the fore an often neglected aspect of the Popper story in the public imagination, that is the deep friendship, collaboration and admiration that characterised this relationship. We can see from the correspondence between Popper and Kraft that at the time when Popper was in the process of publishing his work on the problems of induction and demarcation in what would later be titled Logik der Forschung (1935), that Popper was constantly seeking Kraft's advice and feedback in relation to his work. For instance, the letters of 1933 show that Popper was particularly concerned with Kraft's opinion on his chapter on Fries which included Kraft's criticism of Kant. Chapter Five on Fries and Kant was perhaps the most important chapter in the original manuscript for Die beiden Grundprobleme as it contained the discussions on the dilemmas of truth and Kant's transcendental method necessary for Popper to propose a solution to the problem of induction.Footnote ⁵⁷

For example, Kraft's criticism of Popper's positions on questions concerning the ‘existence’ and ‘possible modes of validation’ of Kant's a priori synthetic proposition, and Fries's psychological deduction and whether or not it was an improvement upon Kant had a lasting effect on the trajectory of Popper's theoretical concerns.Footnote ⁵⁸ Kraft's main concern was that Popper's attitude implied that we should give up the idea of objective truth, a position which Popper believed that he could not satisfactorily answer until he came across Tarski's ‘clarification of the correspondence theory of truth’.Footnote ⁵⁹ The problems concerning Popper's theorising on truth and the relativist and sceptical leanings are evident in an early discussion in Die beiden Grundprobleme just before Popper begins a discussion on Fries which relies heavily on Kraft's Von Husserl zu Heidegger. The importance of resolving this criticism from his friend may be responsible for the immediate and emphatic manner in which Popper accepted Tarski's thought. The trajectory in which Popper later developed his theorising on truth and objectivity ought to also be seen as part of a life-long response to Kraft. Without this friendship it is doubtful whether Popper would have written anything like The Open Society. Much of the lack of attention that Kraft receives in regards to discussions of Popper may be due to the fact that despite Popper's indebtedness to Kraft for his understanding of Fries and perhaps Kant as well, it is difficult to find evidence of this. Popper did not mention Kraft once in the text of his discussion of Fries and Kant in Chapter Five of Die beiden Grundprobleme despite extensively citing Kraft in the footnotes. Later in The Open Society Popper would treat Tarski in much the same way, reflecting a pattern of referencing that would have a lasting impact on our appreciation of the influences on Popper's thought.

4. The Renewal of Kant's Enlightenment

It is pertinent that I make a short digression into Popper's Kantian understanding of Enlightenment thought. The philosophy of Karl Popper can be seen as a continuation of the German Aufklärung tradition. This point has previously been raised by Kurt Salamun who argued that the ethos of Popper's critical rationalism was fundamentally that of the Aufklärung.Footnote ⁶⁰ Popper's credo: ‘I may be wrong and you may be right, and by an effort, we may get nearer to the truth’,Footnote ⁶¹ ought to be taken as a reaffirmation of this Kantian late-Enlightenment ethos in the twentieth century. Locating Popper's thought within the German Enlightenment ought not to prevent us from perceiving similarities with other Enlightenment figures, particularly those of France and Britain. Direct reference to French Enlightenment figures and their thought is sparse in Popper's work. Despite the ease with which Popper discussed Kant, his discomfort with lengthy discussions on other Enlightenment figures was clearly evident. This was particularly evident when he declined Hayek's recommendation to write a middle part for The Open Society dealing with figures such as Bacon, Hobbes, Descartes and Rousseau.Footnote ⁶² Hayek even suggested to him in a letter that Popper was uncomfortable in systematically treating the figures of the English, Scottish and French Enlightenments.Footnote ⁶³ A familiarity with the works of J. S. Mill (which he inherited from his father), as well as the central arguments in Locke and Hume's philosophies of science remain notable exceptions. The clarity, systemacity and depth with which he treated such arguments as Locke's ‘Bucket Theory’Footnote ⁶⁴ and ‘Hume's problem’, reveal an attitude towards the practice of philosophy as one of dealing seriously with ‘real’ problems,Footnote ⁶⁵ rather than the more historical method of creating discussions which refer to each and every thinker who held a position on a problem even if only in passing.Footnote ⁶⁶

Popper clearly saw himself as heir to a tradition epitomised by Voltaire. Rather than looking at his better known political works for evidence of this we must turn to Woran glaubt der Westen? Footnote ⁶⁷ A lecture give in Zürich in 1958, which reveals much about Popper's philosophical attitude, yet remains unknown to political theorists outside a small contingent of Popper scholars. This lecture emphasised the role of Voltaire for the Enlightenment which was characteristic of the type of rationalism which Popper sought to revitalise for a post-war Europe:

The connection that Popper refers to here is an understanding of rationalism associated with the ‘great prophets’ espoused by the likes of Fichte, Schelling and Hegel. This latter type of rationalism is well known to readers of The Open Society as being a central point of opposition to the ‘critical rational’ or empirical-deductivist philosophy that Popper espoused. This however, does not mean that Popper was not a rationalist. He was both in the sense of being anti-irrationalist and an apriorist. Popper's later ontology, evident in Objective Knowledge: An Evolutionary Approach (1972), is a testament to the apriorism, albeit hypothetical, that existed alongside his empiricism. The opposition between empiricism and rationalism for Popper was not as pressing as the opposition between one mode of ‘prophetic’ rationalism and another Voltairean ‘sober’ rationalism of a ‘give and take’ attitude.

Popper's critical rationalism has best been summarised by David Miller in Out of Error (2006):

If rationality is wholly a matter of method, as Miller describes it, then exploring the changes in Popper's methodological thought is a necessary step in order to scrutinise his understanding of rationality.