From: Philosophy Research Archives X, (1984) pp. 501-511


The Hans Reichenbach Correspondence(1)
An Overview
Saul Traiger
Department of Philosophy
Occidental College
Los Angeles, CA 90041

The Hans Reichenbach Collection is part of the Archives of Twentieth Century Philosophy of Science, which also houses the Rudolf Carnap and Frank Ramsey Collections. The Archives of Twentieth Century Philosophy of Science is located in the Special Collections Department of the University of Pittsburgh's Hillman Library. In the past few years work on the recently acquired Hans Reichenbach Collection has resulted in a useful research source. Although the collection contains many notes, manuscripts, and recordings, efforts at organizing the collection have centered on the wealth of correspondence contained in the collection. A great deal of this organizational work has now been completed, and this part of the collection is open to study by interested scholars.

What follows is an overview of the correspondence catalogued in the collection. All of the information recorded here has been found in the many thousand letters to and from Reichenbach which make up only a portion of the collection. The purpose of this essay is both to acquaint the philosophical public with the wealth of material in this research source and to argue for the importance of this material for the history of recent philosophy.

The Nature and Scope of the Correspondence

The correspondence spans the period from 1919 to 1970. Although Hans Reichenbach died in the Spring of l953, there are many letters which postdate his death, the letters of his widow, Maria Reichenbach. Maria Reichenbach played a major role in the posthumous publication of many of her husband's works and her correspondence largely concerns such issues. The correspondence of Hans Reichenbach begins with the year 1919. At that time, Reichenbach was an Assistent in Philosophy at the University of Stuttgart. The correspondence follows his career to Berlin, Istanbul, and Los Angeles. In addition to the letters, postcards, notes, and announcements which

Reichenbach received, there are carbon copies of the letters and postcards Reichenbach sent. Except for the earliest correspondence, Reichenbach's own letters are exclusively type-written.

There are approximately 9,000 items of correspondence. Reichenbach meticulously saved and maintained his mail, telegrams, and memos. For example, located in the collection are such personal items as announcements from an Alpine hiking club and a motorcycle club; Reichenbach was a member of both. These non-philosophical items provide evidence of Reichenbach the man and would be invaluable to a biographer. Reichenbach also saved announcements of philosophical and scientific meetings, as well as journal announcements and advertisements for new scholarly works.

On the whole, the correspondence is professional. Its content reflects Reichenbach's activities as a philosopher, academician, and popular author. Since Reichenbach was often closer ideologically to scientists than to philosophers, particularly in the early years, much of his correspondence is with scientists, including frequent exchanges with such prominent physicists as Albert Einstein and Max Planck. Once settled in the United States, Reichenbach corresponded principally with philosophers. This is an important difference between the early and late correspondence. Reichenbach's correspondents fall into four major categories. First, Reichenbach had many students over the course of his career; among them were Carl G. Hempel, Kurt Grelling, Martin Strauss, Hilary Putnam, and Wesley Salmon. Many of Reichenbach's students are active and influential philosophers and a great deal about their philosophical development can learned from their correspondence with their teacher. The correspondence with scientists comprises a second category. The bulk of correspondence belongs in a third category, the correspondence between Reichenbach and his peers in philosophy. A few figures will give the reader some idea of the scope of this category of correspondence. There are approximately 200 letters between Reichenbach and Rudolf Carnap, 138 between Reichenbach and Herbert Feigl, 80 between Reichenbach and Sidney Hook, 27 between Reichenbach and C. I. Lewis, and 43 between Reichenbach and Otto Neurath.

The fourth category comprises letters to and from various publishers. In this group of letters we find the day to day progress and roadblocks to Reichenbach's publications. As I will point out shortly, Felix Meiner, the German publisher, played a crucial role in the development of Erkenntnis, the journal which Reichenbach founded. In the United States, California University Press was Reichenbach's main publisher. The correspondence shows that Reichenbach had difficulty in finding a publisher for some of his books. For example, Reichenbach sent the manuscript of The Rise of Scientific Philosophy to more than ten publishers before it was finally accepted for publication by California University Press.

The Reichenbach correspondence, then, is not composed merely of Reichenbach's own letters, but also those of many important philosophers as well. For a significant number of philosophers, we have, on a smaller scale, the same kind of access to a portion of their unpublished writings which we have to Reichenbach's own. We cannot assume that each of Reichenbach's correspondents preserved their own letters as Reichenbach did. Thus the Reichenbach correspondence likely houses significant unpublished material of many philosophers which may not be available elsewhere.

While Reichenbach was a maverick philosopher in pre-war Germany, often at odds with the established powers in academia, the correspondence shows that he did communicate with many of those solidly outside his methodological and doctrinal camp. There is correspondence, for example, with H. Dingler, K. Jaspers, and H. Vaihinger, to name only the most prominent philosophers far a field from Reichenbach's brand of logical empiricism.

A great deal can be learned about the views of a philosopher by noticing with whom that philosopher did not correspond. While Reichenbach was in touch with very many of the important philosophers of his day, a detailed search through the correspondence reveals that he had virtually no contact with Ludwig Wittgenstein. This is quite noteworthy, since the influence of Wittgenstein on the Vienna Circle, of which Reichenbach is often mistakenly believed to have been a member, was enormous. Yet there are no letters between Reichenbach and Wittgenstein, and there are almost no references to Wittgenstein in Reichenbach's letters. This is even more surprising when it is noticed that Reichenbach corresponded regularly with Moritz Schlick and other members of the Vienna Circle who were in regular contact with Wittgenstein.

The fact that Wittgenstein's name almost never appears in the correspondence supports the claim, which will be elaborated below, that the work of Reichenbach and his Berlin Circle must not be confused with that of the Vienna Circle.

Academic Insecurity

A great deal of information concerning Reichenbach's academic movement from university to university, country to country, is contained in the pages of his correspondence. Reichenbach's academic insecurity was the result of many pressures; academic, political, and social. Reichenbach could not have begun his philosophical career at a more unfavorable time. Efforts to promote his views and to secure an academic post were constantly thwarted by the conditions of prewar Germany. Numerous letters show that like many others, Reichenbach was too caught up in his own field to realize that his difficulties were symptomatic of larger problems in German society. However, Reichenbach was able to remain remarkably productive, even under the most trying of circumstances.

In 1919 Reichenbach was a Privat-Dozent in philosophy in Stuttgart. Already well known in philosophical and scientific circles, Reichenbach was hoping for an appointment to a "Lehrstuhl", a chair in philosophy. As the correspondence through 1933 reveals, despite his own strenuous efforts, as well as the efforts of prominent scientists and philosophers on his behalf, Reichenbach never had that hope fulfilled. Reichenbach was considered radical in his interests in the philosophy of science, a field which at that time had no established name. (The contemporary German term for the field is "Wissenschaftstheorie." This term does not appear in the early correspondence.) Reichenbach's philosophical writing was highly technical and closely tied to the work of physicists. The general philosophical climate was unsympathetic and Reichenbach's difficulties in securing a suitable academic position were largely a consequence of this.

In l925 Reichenbach was appointed not to a full professorship in philosophy, but instead to a special assistant professorship in the physics department of the University of Berlin. That this position turned out to be hardly a promotion is clear from the fact that Reichenbach's acceptance of it involved a cut in salary from his position in Stuttgart. Einstein, Planck, and von Laue were instrumental in securing the Berlin position, although they had tried, without success, to secure Reichenbach a full professorship.

Although the physicists were generally supportive, Reichenbach encountered difficulties with Max Planck, for example, as a result of Reichenbach's history of political activism. When Reichenbach was being considered for the Berlin post it was brought to the attention of Max Planck that Reichenbach had, as a student, published a political tract in a student newspaper. In that piece Reichenbach had advocated, among other things, socialist revolution in the university. The revelation of this to Planck almost resulted in Planck's withdrawal of support for Reichenbach's attempts at academic advancement in Berlin. Apparently Planck had asked Reichenbach whether he had been politically active and Reichenbach had denied any political activity. After the publication was revealed, Planck's support of Reichenbach was put in jeopardy. Reichenbach claimed to have forgotten publishing the piece, and denied that it was a genuine publication once it was revealed. After much maneuvering, Reichenbach succeeded in regaining Planck's support, and in assuring the Berlin administration that he harbored no plans to bring about a revolution in the university.

This incident, which significantly delayed Reichenbach's assumption of the Berlin post, is important for many reasons. First, it is likely that the incident arose because someone unsympathetic to Reichenbach's candidacy brought the matter to Planck's attention, in the hopes of ruining Reichenbach's prospects. Whatever the origin of the incident, it is clear that promotion in German universities was a highly political matter and academic freedom was much restricted. Planck's involvement, which is evidenced in numerous letters, shows that even the greatest scientific minds in prewar Germany were often preoccupied with such matters.

Reichenbach taught at the University of Berlin until the Fall of l933 when he was suddenly dismissed from the university under the government's so-called "Race Laws". Reichenbach's academic career in his native Germany was brought to an abrupt close in the Fall of 1933; he was notified of his immediate dismissal from the University of Berlin. Reichenbach had Jewish grandparents on his father's side, and so failed to meet the conditions of Aryan purity stipulated by the government. Evidence of anti-Semitism appears in the correspondence of earlier years. For example, Reichenbach received a letter from a scientific journal to which he regularly contributed, requesting that he certify his Aryan ancestry. The journal explained that it was no longer accepting submissions from non-Aryan authors. It appears that Reichenbach did not answer this request, but there is an exclamation point in the margin of the journal's letter in Reichenbach's pen.

In spite of such evidence, Reichenbach did not suspect that his position and his life were in jeopardy until mass dismissals took place. The correspondence shows that Reichenbach did not plan to leave Germany until he was dismissed from his position in Berlin.

Shortly after his dismissal, Reichenbach went to Istanbul along with a score of other German scholars. Capitalizing on the brain-drain from Germany, Turkey created a new university, recruiting a faculty staffed almost exclusively with displaced German professors. Many of those who found asylum in Turkey were, like Reichenbach, established scholars in Germany. Included among them were the astronomer Ernest Freudlich and the mathematician Richard von Mises. Turkey lacked the academic facilities for a university, but the Turkish government promised to bring the library, classrooms, and laboratories up to the standards of those who were to make use of them. Reichenbach and the others signed five year contracts with the Turkish government. One condition of the contract was that professors had to learn Turkish within five years and thereafter teach all classes in Turkish.

In a letter to Walter Dubislav, a member of Reichenbach's philosophical circle in Berlin, Reichenbach provides a detailed account of his situation in Istanbul. Reichenbach describes the university, the caliber of his students, his teaching methods, and the language problem. Although the position in Istanbul provided Reichenbach with a measure of security, the adjustment was not an easy one and certain problems were never resolved. Reichenbach had been promised a free hand and a large budget for books. However, he complained in letters that most of the books ordered never arrived, even after a number of years. Reichenbach eventually learned that the money for the books had been "lost" in the chain of government officials through which book orders passed.

Lecturing in German with a Turkish student translating into Turkish for the students proved to make teaching difficult, but what frustrated Reichenbach the most was the general lack of intellectual preparedness of his students. After teaching students such as Hempel and Grelling, Reichenbach found himself trying to teach students who had no background in the history of science and philosophy. As a result, he rarely taught his specialty in Turkey; instead he concentrated on the history of philosophy. As he came to express in many letters, Reichenbach felt that the Turkish government's plan for a university had been misconceived. He believed that a university could only flourish where basic human needs had been met, and that they had not yet been adequately met in Turkey.

Reichenbach had other fundamental problems with the University of Istanbul. Through correspondence with Sidney Hook and others, a one year visiting professorship at New York University had been arranged. The appointment conflicted, however, with Reichenbach's contractual obligations at the University of Istanbul. The administrators refused Reichenbach's request for a leave of absence. More than the loss of an important academic opportunity,

Reichenbach deeply resented the way the his superiors handled the matter. Upon learning of NYU's offer, the Istanbul administration wrote to NYU refusing the offer for Reichenbach, without ever consulting him! Together with the other problems, this last matter solidified Reichenbach's resolve to leave Turkey at the end of his five year contract and find a permanent position elsewhere.

Reichenbach had chosen Istanbul over a one year position at Oxford. In letters in which he refuses the Oxford job, Reichenbach gives as reasons the fact that the Istanbul job was for an "Ordinariat" (a full professorship). Years later, Reichenbach was to regret making the decision against Oxford and for Istanbul.

Although isolated from the philosophical world and deeply aware of the lack of his old Berlin circle, Reichenbach was extremely productive during the Istanbul years. In fact, it appears that he turned the isolation and adversity to a positive advantage. The correspondence during this period is extremely large. Reichenbach nurtured his correspondence with philosophers all over the world, but the correspondence to American philosophers is perhaps the largest. Without textbooks for his students, Reichenbach prepared his own texts. The original manuscript of his Elements of Symbolic Logic was written for this purpose. Reichenbach's first philosophical book published in English was accomplished while he was in Turkey. Experience and Prediction, which counts among the most important of Reichenbach's works, was published by Chicago University Press. Charles Morris played a major role in helping Reichenbach to bring the manuscript of Experience and Prediction to press in English and later in helping Reichenbach to find a suitable academic position in the United States. From Istanbul Reichenbach went to UCLA, where he remained for the rest of his life.

Spokesman for Science

Throughout his professional life, Hans Reichenbach wrote popular accounts of scientific developments, and of modern physics in particular. A student of Albert Einstein, Reichenbach combined his ability to make abstract ideas seem concrete with his knowledge of contemporary science to serve as the interface between the cutting edge of science and the culture at large. The correspondence reveals the enormous scope of Reichenbach's efforts to bring science to the layperson, and thus of the great interest in science which fueled his efforts.

One motive for Reichenbach to engage in popular writing was admittedly financial. Only by earning money as a popular author and radio lecturer was Reichenbach able to manage.

Writing popularizations of scientific results and theories became a lifelong occupation, long after it ceased to be a financial concern, and it is clear from letters that Reichenbach was very concerned with the layperson's understanding of both science and philosophy. There are letters from laypersons throughout the correspondence which Reichenbach answered consistently with patience and concern.

In the correspondence one finds evidence of the vastness of Reichenbach's popular writings. From 1920 on, he published popular pieces on the theory of relativity, on radio, on the impact of radio technology on culture, as well as monographs on the history of astronomy and physics. These writings appeared in popular German periodicals such as Die Neue Rundschau and Die Umschau. In the early thirties Reichenbach became the science editor for Die Deutsche Welle, the national radio station for Germany. In this position Reichenbach nurtured the public thirst for news of science.

Of all his books, the one most widely read in Reichenbach's lifetime was The Rise of Scientific Philosophy. While he continued to write for general audience periodicals in the United States, most of Reichenbach's efforts in popular writing were focused on this book. It turned out to be the most difficult book for which to secure a publisher, but also the most financially successful of his publications.


Once installed in Berlin, the activity most prominently reflected in the correspondence is Reichenbach's editorship of the journal Erkenntnis, which he founded. Starting a journal was an intellectual necessity for Reichenbach. Organizing methodologically like-minded philosophers was the only way Reichenbach could influence the philosophical public, since without a professorship in philosophy the usual academic routes were barred. As elsewhere, Reichenbach reveals himself as a masterful organizer.

Several hundred letters concern Erkenntnis which was jointly edited by Reichenbach and Carnap. There are both letters in which Reichenbach solicits manuscripts for his journal from well known philosophers such as Cassirer, and letters in which Reichenbach considers for publication papers from lesser known philosophers. In many letters Reichenbach attempts to clarify the position of the Berlin and Vienna groups to those who inquire about it.

In numerous letters between Reichenbach and Felix Meiner, the famous German publisher, the birth of Erkenntnis unfolds. The publication was delayed for years. Meiner was an active participant and had a genuine interest in the philosophical success of the journal. When Meiner continued to publish Erkenntnis after Reichenbach had left Germany, he did so not without political risk.

The project of Erkenntnis, if not completely Reichenbach's own, is clearly mostly Reichenbach's. In the evolution of Erkenntnis we find Reichenbach in close association with the Vienna Circle. But here the differences surface as well. In a remarkable letter, Schlick tells Reichenbach that he cannot serve as a co-editor of Erkenntnis with Reichenbach and Carnap, as originally planned, because he was not sure that the journal was headed philosophically in a direction he could endorse.

When, in 1933 Reichenbach was forced to leave Germany for Turkey, he retained editorship of the journal. From Istanbul, Reichenbach continued to publish Erkenntnis until, as a letter from Reichenbach to Cambridge University Press reveals, Felix Meiner was forced by the German government to give up publication.

A set of letters between Otto Neurath and Reichenbach provides important information about the transition from Erkenntnis to the Encyclopedia of Unified Science. After publication of Erkenntnis ceased, those who had been involved with it immediately looked for another vehicle of publication. At the time the plans for the Encyclopedia began to emerge, Reichenbach was still in Turkey and unable to be directly involved in the formulation of these plans. Once it was decided that monographs on various subjects would be published, the matter of who would write which monograph arose. When Reichenbach was not offered the monograph on probability theory, he became quite upset. The matter was never completely resolved to Reichenbach's satisfaction, and it became clear that whatever authority Reichenbach enjoyed as editor of Erkenntnis was lost in the transition to the Encyclopedia.

It is striking to find that the correspondence in the later years, when Reichenbach was already firmly established in the United States often deals with plans to establish a new journal, or to resume publication of the original Erkenntnis. Apparently, even with his improved status in the academic world, Reichenbach felt a strong need to head his own journal. This felt need was never fulfilled.

Relation to the Vienna Circle

One of the most important philosophical issues which comes to light in the correspondence concerns the difference between Reichenbach and the Vienna Circle. In many letters he takes great pains to distinguish his position from that of the Vienna circle. One way in which the difference comes out is through letters between Reichenbach and Carnap and letters between Reichenbach and Schlick. Reichenbach wrote a piece for the preface of the very first issue of Erkenntnis. It was supposed to be signed jointly by Reichenbach, Carnap, and Schlick.

However, neither Carnap nor Schlick would agree to sign it, since they found it philosophically repugnant. It was in part a result of their differences concerning the initial statement of the purpose of the journal that Schlick declined as editor.

There are many striking and important letters concerning Reichenbach's relation to the Vienna Circle; I will mention just two. As Reichenbach's dissertation student, Carl Hempel spent most of his time studying with Reichenbach in Berlin. Hempel did, however, spend a semester in Vienna studying with Schlick, Carnap, Waismann, and others in 1929. In a five page letter to Reichenbach, Hempel reports on philosophy in Vienna, describing in detail the syllabus for each course, the works read, and those works ignored. Hempel was surprised to hear so much talk about Wittgenstein, and the extent to which Wittgenstein's works were being discussed in Vienna. The letter describes the teaching techniques of Schlick and Carnap, and the general social life of the Vienna Circle.

Another letter which addresses the question of Reichenbach's relation to the Vienna Circle was written by F.S.C. Northrop. Northrop expresses his concern about the positivist's zeal in disposing of metaphysics, and he claims that Reichenbach's own position should not be confused with that of Carnap and the Vienna Circle. Northrop tells Reichenbach that as he understands him, Reichenbach holds an inductive attitude toward metaphysics, which is something completely different from positivism. Reichenbach accepted this characterization of his views.

Life in the United States

Reichenbach quickly adjusted to the United States and to UCLA. The only time he contemplated leaving UCLA was during the early forties, when his classification as an "enemy alien" put his academic position in question. As an enemy alien, Reichenbach could not leave his house in the evening, and could only leave town with special police permission. Reichenbach endured this status for a time during the Second World War.

Already possessing a good knowledge of English, Reichenbach did not find it difficult to lecture or write in English, and he made a conscious decision to do philosophy only in English; even his letters to Carnap from this period are in English. The correspondence of this period reveals

few problems, and Reichenbach was largely able to resume the activity that characterized his Berlin circle: working closely with students, lecturing in public forums, and writing a great deal. Numerous letters between Reichenbach and his students at UCLA attest to the fact that Reichenbach was extremely popular as a teacher and dissertation director, and that he took a personal interest in the well-being of his students.

While Reichenbach was now on the same side of the ocean as many of his former German colleagues, his duties at UCLA kept him from extensive travel, particularly in the early years.  Consequently, the volume of correspondence between Reichenbach and such philosophers as Carnap, Feigl, and Hempel, is no less voluminous than in the prewar years. Feigl's letters are witty and polemical. Carnap and Reichenbach devoted most of their letters to issues in the interpretation of probability. An exception to this is a series of letters which concern an invitation to Carnap to teach at UCLA. Carnap refused the offer because the state of California required employees to sign a loyalty oath.

Reichenbach accepted the invitation to deliver the William James Lectures at Harvard University, an invitation extended in a letter from W.V.O. Quine. That Reichenbach regarded this as a great honor is apparent from his acceptance letter to Quine. After a lifetime strewn with obstacles to his intellectual pursuit, Reichenbach found at the end of his life that his path was much easier. Reichenbach died suddenly in his study in the Spring of 1953 of a heart attack and thus did not deliver the William James Lectures.

Philosophical Significance

Until recently, Reichenbach's philosophy could only be judged by those works which Reichenbach published. While those works are extensive, they comprise only a fraction of the writings of Hans Reichenbach. It should be obvious, in light of what has already been said, that the correspondence contains a wealth of information about the history of recent philosophy. It contains a great deal of original philosophy as well. To learn that there is fundamental disagreement between Reichenbach and Carnap on the interpretation of probability we need only compare their published works, or read some piece which makes reference to them both; but if we are interested in finding out how each of these philosophers defended and modified his views in light of the criticisms of the other, we need to look at the volume of correspondence between them.

Contemporary philosophy owes much to what is generally called "Logical Positivism". Many of today's philosophical concerns can be seen as attempts to deal with inadequacies in the views of philosophers such as Reichenbach, Carnap, Schlick and their contemporaries. However glaring the inadequacies of the views they espoused, understanding the works of these philosophers is crucial to understanding much of contemporary philosophy. Thus it is important that we correctly understand the views of those to whom we owe part of our philosophical roots. There is the risk that we will oversimplify our past, conceiving it to be one view, rather than a set of related views.

Reichenbach stressed his differences with the Logical Positivists to the point of denying that he was one himself. He was not a member of the Vienna Circle, and his own Berlin Circle was philosophically as well as geographically distinct from it. Perhaps the philosophically most significant theme of the correspondence is the contrast between the two circles which comes through in letter after letter. Important contrasts between Reichenbach and other philosophers can be found as specifically on matters such as the interpretation of probability, the problem of induction, ontological commitment, the interpretation of counterfactuals, the nature of time, and the cognitive significance of moral claims. An examination of these matters based on material found in the correspondence will lead to a revision of the received views about this era in the history of philosophy.

1. I'd like to thank Wesley C. Salmon and Robert Turnbull for helpful suggestions on earlier versions of this paper.