Jørgen Jørgensen’s Relation to Logical Positivism

In: Danish Yearbook of Philosophy
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Between the two World Wars, Jørgen Jørgensen was a central figure in Danish philosophy and internationally recognized, as his teacher Harald Høffding had been before World War 1. When in the late 1920s Jørgensen established contact with the movement that would later be called logical positivism, he found a group of philosophers of his own age who advocated empiricism, the tools of formal logic and the Unity of Science, and who shared his anti-metaphysical approach to philosophy. He became one of the movement’s organizers and wrote its history, but he was only for a short period influenced by especially Rudolf Carnap’s philosophy of logic. Although Jørgensen was never an uncritical member of the movement, he is often considered as a central representative of logical positivism in Scandinavia.


Between the two World Wars, Jørgen Jørgensen was a central figure in Danish philosophy and internationally recognized, as his teacher Harald Høffding had been before World War 1. When in the late 1920s Jørgensen established contact with the movement that would later be called logical positivism, he found a group of philosophers of his own age who advocated empiricism, the tools of formal logic and the Unity of Science, and who shared his anti-metaphysical approach to philosophy. He became one of the movement’s organizers and wrote its history, but he was only for a short period influenced by especially Rudolf Carnap’s philosophy of logic. Although Jørgensen was never an uncritical member of the movement, he is often considered as a central representative of logical positivism in Scandinavia.


At the Seventh International Congress of Philosophy in Oxford in 1930,1 the Danish philosopher Jørgen Jørgensen (1894–1969), professor of philosophy at the University of Copenhagen from 1926 to 1964, met a number of members of the Vienna Circle, among them Rudolf Carnap, Otto Neurath and Moritz Schlick. He attended Schlick’s lecture on “The Future of Philosophy”,2 and he himself delivered a talk on the metaphysical implications of modern physical theories.3 He made a very favourable impression, which led to his appointment as a member of the permanent International Committee for Congresses of Philosophy, a membership that would last until 1950, and to an invitation from Schlick, Léon Brunschwicg and Federigo Enriques to contribute to their respective journals.

In 1931, Carnap sent his Abriss der Logistik (1929) to Jørgensen, who mentioned in his letter of thanks that he had already read Carnap’s Der logische Aufbau der Welt from 1928.4 In March of 1932, Jørgensen was invited to Berlin by Hans Reichenbach to give a guest lecture on logistics, i.e. the logical system developed by Russell and Whitehead.5 Later that year, Jørgensen arranged for both Carnap and Neurath to lecture in Copenhagen. Prior to Jørgensen’s visit to Berlin, Carnap had sent him parts of the manuscript for Logische Syntax der Sprache, which would be the subject of discussions between the two of them in Berlin and later on in Copenhagen. Jørgensen has informed the author of this article that it was he who suggested the book’s title. Upon its publication, Jørgensen wrote an enthusiastic review of it in Erkenntnis.6 It is thus clear that Jørgensen had been accepted as a member of the circle surrounding Schlick and of the movement that its followers called “our circle” or “our movement”. He quickly got involved both in publication projects and organizational work.7At the Congress of Scientific Philosophy in Paris 1935, it was decided that future congresses would promote the preparation of an International Encyclopedia of Unified Science, and a committee was set up to organize the work, consisting of Jørgensen, Neurath, Carnap, Philipp Frank, Charles William Morris and Louis Rougier. At the Congress of Logical Positivism in Cambridge in 1938, Jørgensen, along with Carnap, Frank and Morris, became involved in the publication of the Library of Unified Science, which would be edited by Neurath. The year before – on February 4th, 1937 – Neurath had proposed that Jørgensen should write the history of logical positivism, to which Jørgensen had agreed, at the same time making it clear that he would not be able to complete the work until the end of 1938. On May 6th, Neurath had accepted this deadline, but the outbreak of World War ii delayed the realization of the project, and it was not until 1951 that Jørgensen’s short book on the history of the movement was published in English.8


At the time Jørgensen established contact with the logical positivists, his philosophical views were already largely settled. His espousal of the movement’s program, as it was expressed, for example, in its 1929 manifesto Wissenschaftliche Weltauffassung. Der Wiener Kreis, thus did not involve the abandonment of earlier positions on his part, but merely indicates that he had found a group of philosophers from his own generation who largely agreed with him on all essential points. His concern that philosophy should be scientific, which entailed rejection of metaphysical speculation and Lebensphilosophie, was echoed in the logical positivists, just as the latter’s empiricism and the resulting doctrine of the unity of science were already firmly established in Jørgensen’s own thinking. The movement’s interest in modern logic and the foundations of mathematics was also shared by Jørgensen, who, under the influence of Carnap’s works from the late 1920s and early 1930s in particular, changed his previous views on the nature of logic and its relation to psychology; the only point on which his encounter with logical positivism would modify his views. However, the change would only be short-lived. Already in the late 1930s, Jørgensen reverted to the views he had formed about logic before his encounter with logical positivism.

Empiricism made its entry into Danish philosophy with Jørgensen’s teacher Harald Høffding (1843–1931), who was the leading Danish philosopher from 1885 to 1925, a position Jørgensen would assume from 1925 to 1950. The empiricism advocated by Høffding throughout his long career was not Comte’s antimetaphysical version, however, but was rather inspired by Herbert Spencer. Like Spencer, Høffding held that empiricism suffered from inherent metaphysical problems, such as the problem of the nature and origin of consciousness; but contrary to Spencer, Høffding considered these metaphysical problems to be philosophically insoluble, because they are beyond the reach of experience. There would thus be no room for metaphysical speculation on his philosophical agenda, and in this sense, his thinking may be termed antimetaphysical. Since experience will never deliver definitive answers, scientific exploration of reality will take the form of a constant approximation to the truth; but this truth itself is merely an ideal, or rather a regulative idea in Kant’s sense, providing constant guidance for the progress of science. Høffding’s empiricism was modified by his theory, inspired by Kant, of the active role of consciousness in cognition, mainly consisting of processes that secure the unity of consciousness. In contrast to Kant, however, Høffding interpreted his transcendental philosophy as a psychology of cognition.

During his student years from 1912 to 1918, the young Jørgensen became an adherent of the anti-metaphysical neo-Kantianism of the Marburg School, which meant that he had to reject Høffding’s empiricism. At the age of 22, he wrote somewhat ironically about “hyper-empirical little Denmark”, which had quite overlooked that once “in a small German university town there lived a man named Kant, who demonstrated a certain genius for articulating and addressing philosophical problems”.9

In the manifesto of the Marburg School, Hermann Cohen and Paul Natorp had stated that “Philosophie ist uns in allen ihren Fragen mit dem Faktum der Wissenschaft, wie dieses sich fortbilden, logisch verbunden. Philosophie ist uns daher die Prinzipienlehre der Wissenschaften […].”10 To the Marburger School, philosophy was coextensive with the philosophy of science, and hence also with scientific and antimetaphysical philosophy. We encounter the same stance in Jørgensen. In his later years, however, he would no longer link his rejection of metaphysical speculation with the neo-Kantianism of his youth, but rather with the anti-religious stance which he – the son of a minister – had expressed already during his school days.11 He pointed to the same origins of the empiricism that characterized his thinking from 1918 and the rest of his life.

One of the reasons why Jørgensen left his neo-Kantian position in 1918 and moved in the direction of phenomenalism was his reading of the young socialist Herbert Iversen’s voluminous work, Two Essays on Our Cognition, which was published in 1918.12 At its publication, Jørgensen wrote a very favourable review.13 In this book, Iversen advocated an extreme empiricism that would radicalize classical British empiricism as articulated by Berkeley and Hume. The work contains a critique of any theory of knowledge that attempts to set forth criteria for the objectivity and validity of human cognition, and one of its main aims is to show that all traditional philosophical problems are pseudo-problems arising from a conflation of two different ways of using language.

Language consists of words to which a sense or meaning is assigned, i.e. they are symbols. When writing about words and their meaning, or simply about symbols in general, Iversen considers both natural languages ​​and the empirical and formal sciences to be symbolic systems, and hence languages. An attempt to clarify the terms “meaning” and “sense” is not to be found in Iversen.

Symbols can be used in two different ways, according to Iversen, depending on which type of psychological situation the symbol user is in. In some situations, use is inhibited, in others it is stimulated. Iversen distinguishes between what he calls “suspicious situations”, i.e. psychological situations in which the symbol user progresses slowly, stopping “at each symbol image and asking for its true meaning and its mental history” and “relaxed situations” where no question is raised as to the “real” meaning of the symbol.14 In relaxed situations we assume that the symbols denote objects, properties and relations between objects in a world existing independenty of us; but when we are suspicious, we realize that we are really only talking about the contents of our own consciousness. And with respect to these, we can only be certain of what we experience at any given moment, i.e. in an instantaneous mental state, which Iversen called “the direct datum”.

When we talk about “validity” or “truth” in “relaxed” situations, we mainly ask whether a certain assumption corresponds to conditions in an independently existing world, and in the vast majority of cases, answering this question will pose no problems. But when we start asking what “validity” really means while still holding on to the distinctions of “subjective / objective” and “certainty /truth”, we confuse the “relaxed” use of the word “validity” with the “suspicious” use in which, with respect to the direct datum, there is no difference between “certainty” and “truth”, and where the mentioned distinctions are hence meaningless. The problem of knowledge, as philosophers conceive it, is therefore a pseudo-problem that arises from the conflation of different languages, ​​or different uses of language. When Jørgensen spoke at the International Congress of Scientific Philosophy in Paris in 1935 about the evolution of empiricism in Scandinavia and spent much of his time expounding Iversen’s view, this was not least because he considered Iversen to be an original precursor of logical positivism.15

The encounter with Iversen’s extreme empiricism seems to have prompted Jørgensen to develop a phenomenalist theory of cognition that evolved into a neutral monism that was probably inspired by Ernst Mach. For example, in the mid-1920s, Jørgensen wrote that

As a matter of fact, we no more experience material bodies or physical forces than we experience souls or spiritual forces. What we experience is a ‘stream’ of so-called conscious phenomena, some of which we gradually learn to interpret as signs of material things and their properties, while learning to interpret the rest as subjective, mental items.16

The “so-called conscious phenomena” were also named “neutral experiences” by Jørgensen.

Thus, in construing “neutral” consciousness phenomena as signs of either material objects or mental items, as the case may be, Jørgensen must presuppose that material objects exist independently of our awareness of them, i.e. Jørgensen tries to combine a (critical) realism with a phenomenalist theory of cognition. On this point he differs from Mach, for whom material objects and mental items are specific connections between intrinsically neutral elements.

The difference between material objects and mental items, Jørgensen further writes, is

that we regard those features of our ‘neutral’ experiences as mental which we have reason to consider to be dependent on the functions of our body and, in particular, the functions of our nervous system, while we consider the features we have reason to consider to be independent of the existence of our body, as material.17

The reasons Jørgensen has in mind for taking some consciousness phenomena to be evidence of material objects, and others to be indicative of something mental, must ultimately be based on conscious phenomena, given his phenomenalist line of thought. Hence, his fusion of realism and phenomenalism seems hardly tenable.

In full agreement with Mach and his English student Karl Pearson, Jørgensen wrote a few years later that the physical conception of the world “is a construction formed by inference from our direct experiences […].”18 It follows that the empirical sciences constitute a uniform class in the sense of being all based on empirical observation and, to a greater or lesser extent, subjecting their claims to empirical testing. This uniformity does not mean that all empirical sciences can be deduced from a basic science, for example from physics, but that all sciences use empirical methods. A major reason why Jørgensen felt at home among the logical positivists was probably that they all, and Neurath in particular, advocated the idea of ​​such a unity. The movement’s 1929 manifesto emphasized that

„Die wissenschaftliche Weltauffassung ist nicht so sehr durch eigene Thesen charakterisiert, als vielmehr durch die grundsätzliche Einstellung, die Geschichtpunkte, die Forschungsrichtung. Als Ziel schwebt die Einheitswissenschaft vor.“19

Jørgensen’s large book from 1927 entitled Philosophical Lectures, planned to serve as a textbook for first-year students at the University of Copenhagen as a propaedeutic to their scientific training, was precisely an attempt to outline the unity of the empirical sciences. It was also recognized as such by Neurath. In a 1938 article on Jørgensen’s book, he wrote that “Joergensen gives in his lectures not only a program of the Unity of Science but he also shows this Unity as an actuality.”20


During his student years, Jørgensen had moved within the philosophical domain staked out by his teacher Høffding, but he had departed from Høffding in embracing neo-kantianism and interpreting Kant’s transcendental philosophy as an epistemology, not as a psychology of cognition. His encounter with Iversen’s empiricism had made him change his mind, however. In addition, Bertrand Russell’s writings on logic and philosophy of mathematics had been brought to Jørgensen’s attention by the young Edgar Rubin, who, like Jørgensen, held a magister’s degree in philosophy but chose a psychological topic for his thesis, and would later become a professor of experimental psychology. This had induced Jørgensen to embark, in the late 1910s and early 1920s, on a comprehensive study of the development of formal logic from George Boole, Ernst Schroeder, Gottlob Frege and Giuseppe Peano to Bertrand Russell and Alfred North Whitehead. This naturally led him to reflect on the relationship between mathematics and logic, and on the nature of logic. Russell became Jørgensens “great role model”, as he wrote in his autobiography.21

At the request of Høffding, among others, and with Jørgensen in mind, the Royal Danish Society of Science and Letters in 1924 announced a prize essay competition with the following topic: “[t]o study the principal forms of general logical theories according to Boole and his successors, to determine their historical development and their relation to classical logic, and to state the position of logic in relation to philosophy and mathematics according to these theories.”22 Jørgensen quickly set to work to answer the assignment, and in a year and a half wrote an essay the printed version of which would run to 1034 pages, while simultanously holding a full-time position in an employers’ association. The large volume reflects the fact that Jørgensen had not restricted himself to delivering what was required to answer the assignment, as he also wanted to write a handbook on modern symbolic logic and the philosophy of logic. His essay was awarded the gold medal, securing Jørgensen a professorship, and was published in English in three major volumes in 1931, entitled A Treatise of Formal Logic, its Evolution and Main Branches, with its Relation to Mathematics and Philosophy.23 In his book, Jørgensen had embraced Russell and Whitehead’s program of deducing mathematics from logic, believing that the problems that had emerged in the implementation of the program could be solved. The very year that Jørgensen’s Treatise was published, however, the program was dealt a death blow by Kurt Gödel; still, in his later years, Jørgensen would not accept Gödel’s demonstration that the program could not be carried out. In accordance with the theory of meaning presented by Wittgenstein in the Tractatus, Jørgensen dismissed the possibility of self-referring sentences, which was presupposed by Gödel’s proof.24

The first volume of Jørgensen’s Treatise contained an account of the evolution of logic from Greek antiquity to the 1920s, while the second volume presented a systematic account of the individual phases of this evolution, concluding with a similarly systematic presentation of the attempts to derive mathematics from logic. The third volume contains Jørgensen’s own contributions to the philosophy of logic and mathematics, including a discussion of Russell and Whitehead’s program. Here, only two problems will be mentioned out of the many discussed by Jørgensen in his Treatise, namely the extent to which the meanings standardly attributed to the logical symbols are relevant to the attempt to establish criteria for logical entailment, and the problem of the relationship between logic and psychology. Jørgensen’s views on these questions were modified quite strongly, if only briefly, through his encounter with logical positivism and especially under the impact of Carnap’s views.


With respect to the first cluster of problems, which would later develop into the issue of the relationship between intensional and extensional logic, it is important to note that Jørgensen’s contribution to the discussion predated the formulation of proper meaning theories by a decade. Hence, when Jørgensen speaks of the “meaning” or “sense of symbols, he uses these terms as they are used in ordinary, everyday language. In an implicit confrontation with David Hilbert’s formalist views, Jørgensen dismissed a nominalist understanding of logic in his Treatise, i.e. one that considers its symbols to be mere signs, the meaning of which is provided by the rules determining in which combinations they may occur: “Logicians cannot […] be nominalists, but must consider throughout the significance of their symbols, and each symbol must have its own quite definite meaning.”25 It is not the rules of their combination that determine their meaning, but their meaning determines the way they are to be used:

[L]ogistic symbols and group of symbols (definitions and propositions) [must] always have a meaning, and it is this meaning which determines the rules for manipulating the symbols.26

In order for the axioms of formal systems to be intelligible, the undefined basic concepts must possess a meaning, and a meaning must be assigned to the defined concepts that can be related to their everyday use.

Therefore, a formalization of e.g. the relation of logical entailment must presuppose that the statements between which the relation is claimed to hold possess a meaning, and the very formalization of the term “if-then” must presuppose that the meaning of the consequent is contained in the meaning of the antecedent. When “if-then” is understood in this way, it is not a truth function, and therefore other criteria must be devised for the existence of a relation of logical entailment than in extensional logic. After the publication of the Treatise, Jørgensen contributed to this discussion and gradually became critical of the possibility of establishing an adequate extensional logic.

Jørgensen’s first contribution to the discussion of extensional versus intensional logics dates from 1932. Here, he writes that if an extensional logic is defined as a logic dealing only with truth functions, and an intensional logic as a logic dealing with the logical relations between the meanings of statements, then it seems that extensional logic, which precisely ignores the meaning of statements, constitutes merely a part of logic and hence needs supplementation. He therefore believes that it might be argued that

eine jede extensionale [Logik eine intensionale]27 voraussetz, denn die Konstruktion der Wahrheitsfunktionen setz voraus, dass die atomare Sätze nicht völlig sinnlos sind, sondern wenigsten so viel Sinn haben, dass man sie voneinander und von ihren Negationen unterscheiden kann. Dagegen scheint das umgekehrte nicht der Fall zu sein, denn man kann sehr wohl erkennen, ob ein Satz einen anderen Satz „entails“, ohne dass man etwas von den Wahrheitswerten der beiden Sätze zu wissen braucht. In diesem Sinn ist also die intensionale Logik fundamentaler als die extensionale, und es scheint verfehlt, die Logik rein extensional aufbauen zu wollen, wie es in “Principia Mathematica” versucht ist.28

If the meaning of statements is a prerequisite for establishing their truth value, which is hard to deny, then logic cannot disregard that meaning. Jørgensen therefore held that the most urgent task of logic was to design an intensional logic.

In 1934, Carnap’s Logische Syntax der Sprache was published. Jørgensen had read the manuscript and discussed the book’s theses with the author prior to its publication. Carnap had argued that in going about its task, which is to formulate criteria for one statement’s following from one or more others, logic need not invoke the meanings of these statements, and had argued that a logic of meaning is unnecessary, as logic is merely syntax, i.e. a system for forming and transforming statements.

In 1936 Jørgensen delivered a series of lectures, published the following year, on the evolution of logic since the 1920s.29 Probably under the influence of Carnap, he had now abandoned the idea that an extensional logic presupposes an intensional logic, and that the rules for the logical connectives follow from the meanings of these terms. And although he would not a priori preclude the possibility of a “higher or deeper logic of ‘content’,”30 he holds, however, that the extant proposals for such logics all suffer from the defect “that they operate with the highly indeterminate and vague concept of meaning which, despite many efforts so far, has resisted clarification.”31 At this time, Jørgensen also seems to have accepted Carnap’s Principle of Tolerance from Logische Syntax der Sprache, which states, among other things, that anyone can build his own logic as he pleases , i.e. build his own language, as long as he spells out the syntax of that language.32 Similarly, Jørgensen wrote:

Different logical games are possible, and one is not bound to choose any particular one of them. But if you decide to play a particular game, then you also have to abide by its rules – if not, it is no longer that very game at all, even if the pieces may appear to be the same. It is not the pieces, but the rules of the game that define it – both that it is a game at all, and which game it is.33

A few years after this announcement, Jørgensen changed position once more. His reorientation – or rather his return to an earlier position – was expressed most clearly in a textbook he published in 1942, in which he wrote:

When you infer from p to q, you not only derive the truth of q from the truth of p, but first and foremost you derive q’s “content” from p’s “content”, and it is really just the possibility of this inference of “content” that guarantees that q is true when p is so. From a true assertion, one cannot infer just any arbitrary true assertion whatever, and in some cases you can infer from p to q even if p is not true. Truth values are thus not at all the primary aspect of inferences, what matters is the ‘content’ of the assertions.34

The relation of entailment is therefore a semantic relation and cannot be characterized purely syntactically.

When Jørgensen encountered logical positivism, he was already an accomplished formal logician who mastered the standard formal systems in which the entailment relation was formalized, and he had a deep knowledge of the philosophy of mathematics. This was also recognized by the other adherents of the movement, and in the period of 1936–42 Jørgensen was a member of the Council of the Association for Symbolic Logic. Over the years, however, his skepticism toward the usefulness of the formal logic on which he had spent so many of his most creative years, would grow. In his 1966 autobiography, he wrote of logic that it “only serves […] to bring system or order to materials discovered by empirical means, but otherwise idles in pure tautology.”35


In his Treatise, Jørgensen discussed the relationship between logic and psychology, but concluded that a definitive answer to the question was not possible because the study of the psychology of thinking was only in its infancy. However, like Høffding, he believed that logic must presuppose empirical knowledge of how human beings actually reason, and that it is the task of logic to investigate whether the extant forms of inference are valid. But since complete empirical knowledge of the workings of human thinking, now and in the future, will never be attained, Jørgensen is forced to conclude:

[L]ogic can never be regarded as having a definitive foundation, for since the forms of rules of operation can only be arrived at by analysis of material procured by induction, we never know whether this is exhausted, or whether new forms and rules yet remain to be found.36

Logic does not – as had been asserted by Russell, for example – relate to a timeless world, but is based on a knowledge of thought processes derived partly from introspection and partly from analyses of linguistic articulations of thought processes, which together form the empirical materials for logic.

After Jørgensen had come to embrace Carnap’s Principle of Tolerance, which entailed a relativistic view of logic, the problem of the relationship between logic and psychology seems to have lost his interest. Instead of emphasizing the empirical basis of logic, which is evident in the Treatise, Jørgensen would stress the existence of conventional elements in logic in his Træk af Deduktionsteoriens Udvikling from 1937:

However, the most important result of general significance brought forth by the recent logical studies, is presumably the demonstration that logic itself, the theoretical stronghold of absolutism, contains an extensive system of conventional elements that can be changed at will to a greater or lesser extent. The syntax of logic can always be adapted to serve present needs, and it depends on the latter which logical “language” is to be preferred in any given case.37

At this point in time, Jørgensen’s conception of the nature of logic coincided with the official position of logical positivism. The formal sciences can be developed independently of experience and say nothing about reality, whereas the material sciences are empirically grounded and have real content.

A few years later, however, Jørgensen would once again change his position. In his large textbook of psychology from the years 1942 to 45, he described logic as an empirical science. He wrote here that

although the sentences of logic [e.g., the theorems of propositional logic] are not about non-linguistic objects and phenomena, they do have an empirical content, however, as they specify how from a given sentence one can infer another sentence which is true if the former is true, i.e. which possesses representational meaning [i.e. has a reality content] if the former has representational meaning, which […] can only be established empirically, namely by documenting the designata of the sentences.38

Although Jørgensen does not explicitly deal with the relationship between logic and psychology in the textbook, it was a subject that constantly engaged him. Even in 1964, he impressed upon a younger colleague that:

Of course, the relationship between logic as a science and psychology as a science, is that psychology is subordinate to logic, i.e. it must be assessed according to the norms of logic – but logic itself is generated by psychological processes and must be “explained” in terms of the latter, which implies that both the existence and the nature of logic must in principle be examined by empirical means […] .39

After having been occupied with the problem of the relationship between logic and psychology for more than 40 years, Jørgensen had thus returned to his starting point, namely in Høffding.


In the members of the group of philosophers and scientists who, despite divergent positions in numerous areas, became part of the movement called “logical positivism” or “logical empiricism”, Jørgensen encountered the same empirical and anti-metaphysical views, the same desire to make philosophy scientific and the same view of the unity of the empirical sciences, that he himself embraced after his break with neo-Kantianism. Despite this break, Jørgensen still adhered to some of the views he had encountered in the Marburger group, for example that the search for truth is an ever-ongoing process, and that philosophy must be the philosophy of science. Only on a single point, viz. concerning the nature of logic, did his views change as a result of his encounter with logical positivism. But this change was only short-lived. There is no doubt that Jørgensen felt comfortable in the circle of logical positivists, but he was no more an orthodox loyalist than were the numerous other individuals who attended the meetings and congresses of the movement. The very notion of an orthodox logical positivist is indeed merely a figment of the imaginations of the movement’s critics.

Jørgensen had only a few students. His critical acuity and his lack of understanding and acceptance of the development of philosophy after 1945 made some philosophy students turn away from him, as the recognition from him that they hankered for – a fact he hardly realized – would not be forthcoming; others appear to have been downright paralyzed by his encyclopedic knowledge. The trend in Danish philosophy after World War ii would also work against him. Justus Hartnack, who served as a professor at the University of Aarhus from 1954 to 1972 and who influenced a generation of Danish philosophers, sought to eliminate the tie between science and philosophy that had been at the heart of logical positivism and of Jørgensen’s thought. Hartnack considered philosophy to be a separate science with its own problems and methods. In his philosophy, Hartnack was influenced by the later Wittgenstein, by Gilbert Ryle and by J.L. Austin.

Another distinctive figure in Danish philosophy was Peter Zinkernagel. He had been Jørgensen’s star pupil during his studies, and Jørgensen had introduced him to physicist and Nobel Laureate Niels Bohr, who would exert a lasting influence upon Zinkernagel’s thinking; but when Zinkernagel submitted his doctoral dissertation, Omverdensproblemet, which was published in 1957, Jørgensen backpedalled, as he could not accept the transcendental-style philosophy that was put forth in the dissertation. His opposition resulted in heated discussions between Jørgensen and Zinkernagel, who was seconded by a group of young philosophers. Their aim was to get Jørgensen to retire from his professorial chair in order for Zinkernagel to replace him. Despite the strain that these discussions put on Jørgensen’s health, he stood firm. Zinkernagel never got a university position, which was due inter alia to the fact that he never applied for one, but instead became some sort of cult figure for segments of the Copenhagen intelligentsia. When the Marxist wave swept across the Danish student population in the late 1960s, Jørgensen was labelled as an orthodox logical positivist. By then, he was too old to take issue with the allegation. Since the 1930s he had declared himself to be a communist, but he was never a Marxist, which would make him a target of criticizism from certain heads of the Danish Communist Party in the 1950s. But back in those days, he knew full well how to defend himself.40


An exposition of Jørgen Jørgensen’s philosophical thinking can be found in C.H. Koch: Dansk filosofi i positivismens tidsalder 1880–1950. Copenhagen: Gyldendal 2004, pp. 187–241. An account of his relation to logical positivism is presented in the same author’s “Jørgen Jørgensen and Logical Positivism” in The Vienna Circle in the Nordic Countries, Vienna Circle Institute Yearbook 14, ed. by J. Manninen and Fr. Stadler, Dordrecht / Heidelberg / London / New York: Springer cop. 2010, pp. 153–166. References to further literature on the subject may also be found here. Passages from the texts mentioned above recur in the present article.


Proceedings of the Seventh International Congress of Philosophy, held at Oxford, Great Britain, September 1–6, 1930. Oxford: Oxford University Press, 1931, pp. 112–116.


“Some Remarks Concerning the Principal Metaphysical Implications of Recent Physical Theories and Points of View”, ibid. pp. 1–8.


See draft of letter to Carnap of September 5th 1931 in Jørgen Jørgensens Papirer, I. Letters, capsule 2, The Royal Library, Copenhagen. Jørgensen’s written communication with the logical positivists consists mainly of letters from Otto Neurath on organizational matters, and Jørgensen’s drafts for answers. Much of the exchange with Neurath concerns the planning of the Second International Congress for the Unity of Science, held in Copenhagen in 1936, for which Jørgensen served as a secretary. Jørgensen’s address at the opening of the congress was published in Erkenntnis, vol. 6, 1936, pp. 278–285.


Jørgensen, J.: “Über die Ziele und Probleme der Logistik”, Erkenntnis, vol. 3, 1932, pp. 73–100.


Erkenntnis, vol. 4, 1934, pp. 419–422.


Details about Jørgensen’s relations with the logical positivists and his participation in their meetings can be found in his autobiography, which appears in Festskrift udgivet af Københavns Universitet i Anledning af Universitetets Årsfest November 1966, Copenhagen: Bianco Luno 1966, pp. 139–149. Jørgensen wrote this short autobiography on the occastion of his being awarded an honorary doctorate by the University of Copenhagen in 1966. His ties to the circle are also laid out in his The Development of Logical Empiricism, which constitutes vol. 2, No. 9 of the International Encyclopedia of Unified Science, Chicago: The University of Chicago Press 1951, especially pages 40–48. An extended Danish version of his account of the history of logical positivism had previously been published in Festskrift udgivet af Københavns ­Universitet i Anledning af Hans Majestæt Kongens Fødselsdag. 11. Marts 1948, Copenhagen: Bianco Luno 1948, pp. 1–97.


The letters from Neurath about the project and the drafts of Jørgensen’s answers can be found in “Jørgen Jørgensens Papirer”, see note 4.


Quoted in C.H. Koch: Dansk filosofi i positivismens tidsalder 1880–1950. Copenhagen: Gyldendal 2004, p. 167.


H. Cohen & P. ​​Natorp: “Zur Einführung”, E. Cassirer: Der kritische Idealismus und die Philosophie des ‘gesunden Menschenverstandes’”, H. Cohen & P. Natorp (eds.): Philosophische Arbeiten, bd. 1, hefte 1, Gieszen: Töpelmann 1906, p. i.


See J. Witt-Hansen’s obituary in Festskrift udgivet af Københavns Universitet i Anledning af Universitetets Årsfest November 1969, Copenhagen: Bianco Luno 1969, p. 243–244.


See C.H. Koch: Dansk filosofi i positivismens tidsalder 1880–1950, Copenhagen: Gyldendal 2004, p. 395–418. Further references are listed here.


”Filosofi og deskriptiv Psykologi” 1–2, Ugens Tilskuer, vol. 9, 1918–19, pp. 161–165, 179–183.


Iversen, H.: To Essays om vor Erkendelse, Copenhagen: Aschehoug 1918, p. 70.


Jørgensen, J.: “The Development of Empiricism in Scandinavia”, Actes du Congrès International de Philosophie Scientifique 8, Paris: Hermann & Cie 1936, pp. 62–67.


Jørgensen, J.: Filosofiske Forelæsninger som Indledning til Videnskabelige Studier, Copenhagen: Levin & Munksgaard 1926–27, p. 544f.


Jørgensen, J., op. cit., p. 545.


Jørgensen, J.: Filosofiens og Opdragelsens Grundproblemer, Copenhagen: Pio 1928, s. 36.

Cfr. K. Pearson: “[T]he universe is largely a construction of each individual mind.” The rammar of Science, 3. ed., London: Macmillan 1911, p. 15.


Wissenschaftliche Weltauffassung. Der Wiener Kreis, Wien: Artur Wolf 1929, p. 15.


Neurath, O.: “Encyclopaedism as a Pedagogical Aim: A Danish Approach”, Philosophy of Science, vol. 5, 1938, p. 492.


Festskrift udgivet af Københavns Universitet i Anledning af Universitetets Årsfest November 1966, Copenhagen: Bianco Luno 1966, p. 145.


Oversigt over Det Kongelige Danske Videnskabernes Selskabs Forhandlinger Juni 1923-Maj 1924, Copenhagen: Høst og Søn 1924, p. 136f.


Reprinted in 1962.


For Jørgensen’s rejection of self-referential sentences, see his article “Some Reflections on Reflexivity”, Mind, N.S. 62, 1953, pp. 289–300. Here, he did not distance himself from Gödel, but later did so in a conversation with the author of this article. In an earlier treatise, „Træk af Deduktionsteoriens Udvikling i den nyere Tid”, Festskrift udgivet af Københavns Universitet i Anledning af Universitetets Årsfest November 1937, Copenhagen: Bianco Luno 1937, p. 111–113, he acknowledged Gödel’s incompleteness proof.


Jørgensen, J.: A Treatise of Formal Logic vols. 1–3, Copenhagen & London: Levin & ­Munksgaard / Oxford University Press 1931, vol. 1, p. 25.


Jørgensen, J., op.cit., vol. 3, p. 145.


The addition in square brackets is Jørgensen’s own and occurs in a special offprint of the article.


Jørgensen, J.: „Über die Ziele und Probleme der Logistik”, Erkenntnis vol. 3, 1932, p. 93.


Jørgensen, J.:: „Træk af Deduktionsteoriens Udvikling i den nyere Tid”, Festskrift udgivet af Københavns Universitet i Anledning af Universitetets Aarsfest November 1937, Copenhagen: Bianco Luno 1937, pp. 3–117.


Jørgensen, J., op. cit., p. 117.


Jørgensen, J., op. cit., p. 102.


Carnap, R.: The Logical Syntax of Language, London: Routledge & Kegan Paul 1959, p. 52 (§17).


Jørgensen, J., op.cit. p. 117.


Jørgensen, J.: Indledning til Logikken og Metodelæren, Copenhagen: Munksgaard 1956 (1942), p. 86.

Festskrift udgivet af Københavns Universitet i Anledning af Universitetets Årsfest November 1966, Copenhagen: Bianco Luno 1966, p. 147.


Jørgensen, J.: Indledning til Logikken og Metodelæren, Copenhagen: Munksgaard 1956 (1942), p. 86.


Jørgensen, J.: A Treatise of Formal Logic, Copenhagen/London: Levin & Munksgaard/­Oxford University Press 1931, vol. 3, p. 207.


Jørgensen, J.: „Træk af Deduktionsteoriens Udvikling i den nyere Tid”, Festskrift udgivet af Københavns Universitet i Anledning af Universitetets Aarsfest November 1937, Copenhagen: Bianco Luno 1937, p. 116.


Jørgensen, J.: Psykologi paa biologisk Grundlag, København: Munksgaard 1957, p. 460.


Witt-Hansen, J: „Jørgen Jørgensen 1. april 1894—30. juli 1969”, Festskrift udgivet af Københavns Universitet i Anledning af Universitetets Årsfest November 1969: Copenhagen: Bianco Luno 1969, p. 246.


Koch, C.H: Dansk Filosofi i Positivismens Tidsalder, Copenhagen: Gyldendal 2004, p. 217f.

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