# Vienna Circle

Moritz Schlick around 1930

The Vienna Circle (in German: der Wiener Kreis) was a group of philosophers who gathered around Moritz Schlick when he was called to a professorship at the University of Vienna in 1922, and organized themselves into a philosophical association named Verein Ernst Mach (Ernst Mach Society). Among its members, besides Schlick, the organizing figure and chairman of the Ernst Mach Society, were Gustav Bergmann, Rudolf Carnap, Herbert Feigl, Philipp Frank, Kurt Gödel, Hans Hahn, Victor Kraft, Karl Menger, Marcel Natkin, Otto Neurath, Olga Hahn-Neurath, Theodor Radakovic, and Friedrich Waismann.

Members of the Vienna Circle had a common attitude towards philosophy, characterized by two main features: first, experience is the only source of knowledge; second, logical analysis performed with the help of symbolic logic is the preferred method for solving philosophical problems. This dual commitment to empiricist positivism and to logic meant that they came to be known as logical positivists—distinguishing them from earlier positivists and empiricists who had not emphasized logic and its role—or logical empiricists, and their program as logical positivism or logical empiricism.

## History of the Vienna Circle

The prehistory of the Vienna Circle began with meetings on the philosophy of science and epistemology from 1907 on, promoted by Philipp Frank, Hans Hahn and Otto Neurath.

Hans Hahn, the older of the three (1879-1934), was a mathematician. He received his degree in mathematics in 1902. Afterwards he studied under the direction of Ludwig Boltzmann in Vienna, and under David Hilbert, Felix Klein and Hermann Minkowski in Göttingen. In 1905 he received the Habilitation in mathematics. He taught at Innsbruck (1905-1906) and Vienna (from 1909).

Otto Neurath (1882-1945) studied sociology, economics and philosophy in Vienna and Berlin. From 1907 to 1914 he taught in Vienna at the Neuen Wiener Handelsakademie (Viennese Commercial Academy). Neurath married Olga, Hahn’s sister, in 1911.

Philipp Frank, the younger of the group (1884-1966), studied physics at Göttingen and Vienna with Ludwig Boltzmann, David Hilbert and Felix Klein. From 1912, he held the chair of theoretical physics in the German University in Prague.

Their meetings were held in Viennese coffeehouses from 1907 onward. Frank remembered:

After 1910 there began in Vienna a movement which regarded Mach’s positivist philosophy of science as having great importance for general intellectual life […] An attempt was made by a group of young men to retain the most essential points of Mach's positivism, especially his stand against the misuse of metaphysics in science. […] To this group belonged the mathematician H. Hahn, the political economist Otto Neurath, and the author of this book [i.e. Frank], at the time an instructor in theoretical physics in Vienna. […] We tried to supplement Mach’s ideas by those of the French philosophy of science of Henri Poincaré and Pierre Duhem, and also to connect them with the investigations in logic of such authors as Couturat, Schröder, Hilbert, etc. (quoted in Uebel 2003, 70)

Presumably the meetings stopped in 1912, when Frank went to Prague, where he held the chair of theoretical physics left vacant by Albert Einstein. Hahn left Vienna during World War I and returned in 1921. The following year Hahn, with the collaboration of Frank, arranged to bring into the group Moritz Schlick, who held the chair of philosophy of the inductive sciences at the University of Vienna. Schlick had already published his two main works Raum und Zeit in die gegenwärtigen Physik (Space and Time in contemporary Physics) in 1917 and Allgemeine Erkenntnislehre (General Theory of Knowledge) in 1918. A central frame of reference for the newly founded discussion group was the Logisch-Philosophische Abhandlung (Tractatus Logico-Philosophicus), published by Ludwig Wittgenstein in 1918. In that book Wittgenstein began by declaring, "The world is all that is the case," and "The world is the totality of facts, not of things." Among its other accomplishments, Wittgenstein's work turned philosophy from an investigation of "the world" or "things" to a primary focus on language or linguistic entities. (Richard Rorty captured this change in philosophical method in his 1967 book, The Linguistic Turn. Chicago: University of Chicago Press.)

Under the direction of Schlick, a new regular series of meetings was begun, and this continued until Schlick's death in 1936. The group usually met on Thursday evenings at the Institute of Mathematics at the university. In 1926 Schlick and Hahn arranged to bring in Rudolf Carnap at the University of Vienna. In 1928 the Verein Ernst Mach (Ernst Mach Society) was founded, with Schlick as chairman. In 1929 the Vienna Circle manifesto Wissenschaftliche Weltauffassung. Der Wiener Kreis (The Scientific Conception of the World. The Vienna Circle) was published. The pamphlet is dedicated to Schlick, and its preface was signed by Hahn, Neurath and Carnap. In the appendix there is the list of the members of the Vienna Circle.

## The Vienna Circle manifesto

The manifesto of the Vienna Circle states the scientific world-conception of the Vienna Circle, which is characterized “essentially by two features. First it is empiricist and positivist: there is knowledge only from experience […] Second, the scientific world-conception is marked by the application of a certain method, namely logical analysis” (The Scientific Conception of the World. The Vienna Circle quoted in Sarkar 1996, 331 – hereinafter VC).

Logical analysis is the method of clarification of philosophical problems; it makes an extensive use of the symbolic logic and distinguishes the Vienna Circle empiricism from earlier versions. The task of philosophy lies in the clarification of problems and assertions through the method of logical analysis.

Logical analysis shows that there are two different kinds of statements—one kind includes statements reducible to simpler statements about the empirically given, the other kind includes statements which cannot be reduced to statements about experience and thus they are devoid of meaning. Metaphysical statements belong to this second kind and therefore they are meaningless. Hence many philosophical problems are rejected as pseudo-problems that arise from logical mistakes, while others are re-interpreted as empirical statements and thus become the subject of scientific inquiries.

One source of the logical mistakes that are at the origins of metaphysics is the ambiguity of natural language. “Ordinary language for instance uses the same part of speech, the substantive, for things (‘apple’) as well as for qualities (‘hardness’), relations (‘friendship’), and processes (‘sleep’); therefore it misleads one into a thing-like conception of functional concepts” (VC 329). Another source of mistakes is “the notion that thinking can either lead to knowledge out of its own resources without using any empirical material, or at least arrive at new contents by an inference from given states of affair” (VC 330). The latter notion is typical in Kantian philosophy, according to which there are synthetic statements a priori that expand knowledge without using experience. Synthetic knowledge a priori is rejected by the Vienna Circle. Mathematics, which at a first sight seems an example of necessarily valid synthetic knowledge derived from pure reason alone, has instead a tautological character, that is, its statements are analytical statements, thus very different from Kantian synthetic statements. The only two kinds of statements accepted by the Vienna Circle are synthetic statements a posteriori (i.e. scientific statements) and analytic statements a priori (i.e. logical and mathematical statements).

However, the persistence of metaphysics is connected not only with logical mistakes but also with “social and economical struggles” (VC 339). Metaphysics and theology are allied to traditional social forms, while the group of people who “faces modern times, rejects these views and takes its stand on the ground of empirical sciences” (VC 339). Thus the struggle between metaphysics and scientific world-conception is not only a struggle between different kinds of philosophies, but it is also—and perhaps primarily—a struggle between different political, social and economical attitudes. Of course, as the manifesto itself acknowledged, “not every adherent of the scientific world-conception will be a fighter” (VC 339). Many historians of the Vienna Circle see in the latter sentence an implicit reference to a contrast between the so-called ‘left wing’ of the Vienna Circle, mainly represented by Neurath and Carnap, and Schlick. The aim of the left wing was to facilitate the penetration of the scientific world-conception in “the forms of personal and public life, in education, upbringing, architecture, and the shaping of economic and social life” (VC 339-340). On the contrary, Schlick was primarily interested in the theoretical study of science and philosophy. Perhaps the sentence “Some, glad of solitude, will lead a withdrawn existence on the icy slopes of logic” (VC 339) is an ironic reference to Schlick.

## Unified Science

The final goal pursued by the Vienna Circle was Unified Science, that is the construction of a "constitutive system" in which every legitimate statement is reduced to the concepts of lower level that refer directly to the given experience. "The endeavour is to link and harmonise the achievements of individual investigators in their various fields of science" (VC 328). From this aim follows the search for clarity, neatness, intersubjectivity, and for a neutral symbolic language that eliminates the problems arising from the ambiguity of natural language. The Vienna Circle published a collection, called Einheitswissenschaft (Unified science), edited by Rudolf Carnap, Philipp Frank, Hans Hahn, Otto Neurath, Joergen Joergensen (after Hahn's death) and Charles Morris (from 1938), whose aim was to present an unified vision of science. After the publication in Europe of seven monographs from 1933 to 1939, the collection was dismissed because of the problems arising from World War II. In 1938 a new series of publications started in the United States. It was the International Encyclopedia of Unified Science, an ambitious, never completed project devoted to unified science. Only the first section,Foundations of the Unity of Sciences, as published; it contains two volumes for a total of 20 monographs published from 1938 to 1969. As remembered by Rudolf Carnap and Charles Morris in the Preface to the 1969 edition of the International Encyclopedia of Unified Science:

The Encyclopedia was in origin the idea of Otto Neurath. It was meant as a manifestation of the unity of science movement […] Original plans for the Encyclopedia were ambitious. In addition to the two introductory volumes, there was to be a section on the methodology of the sciences, one on the existing state of the unification of sciences, and possibly a section on the application of the sciences. It was planned that the work in its entirety would comprise about twenty-six volumes (260 monographs). (Foundations of the Unity of Sciences 1, 1969, vii)

The well known work by Thomas Kuhn, The Structure of Scientific Revolutions, was—ironically enough, given its anti-foundationalist, anti-verificationist, anti-logicist stance—published in this Encyclopedia in 1962, as the number two in the second volume.

## The elimination of metaphysics

The attitude of Vienna Circle towards metaphysics is well expressed by Carnap in the article 'Überwindung der Metaphysik durch Logische Analyse der Sprache' in Erkenntnis, vol. 2, 1932[1] A language, says Carnap, consists of a vocabulary, i.e. a set of meaningful words, and a syntax, i.e. a set of rules governing the formation of sentences from the words of the vocabulary. Pseudo-statements (sequences of words that at first sight resemble statements but in reality have no meaning) are formed in two ways: either meaningless words occur in them, or they are formed in an invalid syntactical way. According to Carnap, pseudo-statements of both kinds occur in metaphysics.

A word W has a meaning if two conditions are satisfied. First, the mode of the occurrence of W in its elementary sentence form (i.e. the simplest sentence form in which W is capable of occurring) must be fixed. Secondly, if W occurs is an elementary sentence S, it is necessary to give an answer to the following questions (that are, according to Carnap, equivalent formulation of the same question):

• (1.) What sentences is S deducible from, and what sentences are deducible from S?
• (2.) Under what conditions is S supposed to be true, and under what conditions false?
• (3.) How S is to verified?
• (4.) What is the meaning of S?

(Carnap, “The Elimination of Metaphysics Through Logical Analysis of Language” quoted in Sarkar, 12)

An example offered by Carnap concerns the word 'arthropode.' The sentence form "the thing x is an arthropode" is an elementary sentence form that is derivable from "x is an animal," "x has a segmented body" and "x has jointed legs." Conversely, these sentences are derivable from "the thing x is an arthropode." Thus, the meaning of the words 'arthropode' is determined.

According to Carnap, many words of metaphysics do not fulfill these requirements and thus they are meaningless. As an example, Carnap considers the word 'principle.' This word has a definite meaning, if the sentence "x is the principle of y" is supposed to be equivalent to the sentence "y exists by virtue of x" or "y arises out of x." The latter sentence is perfectly clear: y arises out of x when x is invariably followed by y, and the invariable association between x and y is empirically verifiable. But, says Carnap, metaphysicians are not satisfied with this interpretation of the meaning of 'principle.' They assert that no empirical relation between x and y can completely explain the meaning of "x is the principle of y," because there is something that cannot be grasped by means of the experience, something for which no empirical criterion can be specified. It is the lacking of any empirical criterion, Carnap believes, that deprives of meaning the word 'principle' when it occurs in metaphysics. Therefore, metaphysical pseudo-statements such as "water is the principle of the word" or "the spirit is the principle of the world" are void of meaning because a meaningless word occurs in them.

However, there are pseudo-statements in which occur only meaningful words; these pseudo-statements are formed in a counter-syntactical way. An example is the word sequence "Caesar is a prime number"; every word has a definite meaning, but the sequence has no meaning. The problem is that "prime number" is a predicate of numbers, not a predicate of human beings. In the example the nonsense is evident; however, in natural language the rules of grammar do not prohibited the formation of analogous meaningless word sequences that are not so easily detectable. In the grammar of natural languages, every sequence of the kind "x is y", where x is a noun and y is a predicate, is acceptable. In fact, in the grammar there is no distinction between predicate which can be affirmed of human beings and predicate which can be affirmed of numbers. So "Caesar is a general" and "Caesar is a prime number" are both well-formed, in contrast for example with "Caesar is and," which is ill-formed. In a logically constructed language, says Carnap, a distinction between the various kinds of predicate is specified, and pseudo-statements as "Caesar is a prime number" are ill-formed.

The main point of Carnap's argument is that metaphysical statements in which meaningless words do not occur are nevertheless meaningless because they are formed in a way which is admissible in natural languages, but not in logically constructed languages. Carnap attempts to indicate the most frequent sources of errors from which metaphysical pseudo-statements can arise. One source of mistakes is the ambiguity of the verb 'to be,' which is sometimes used as a copula ("I am hungry") and sometimes to designate existence ("I am"). The latter statement incorrectly suggests a predicative form, and thus it suggests that existence is a predicate. Only modern logic, with the introduction of an explicit sign to designate existence (the sign $\exists \;$), which occurs only in statements such as $\exists \;xP(x)$, never as a predicate, has showed that existence is not a predicate, and thus has revealed the logical error from which pseudo-statements such as "cogito, ergo sum" has aroused.

Another source of mistakes is type confusions, in which a predicate of a kind is used as a predicate of another kind. For example the pseudo-statements "we know the Nothing" is analogous to "we know the rain", but while the latter is well-formed, the former is ill-formed, at least in a logically constructed language, because 'Nothing' is incorrectly used as a noun. In a formal language, 'Nothing' only means $\lnot \;\exists \;x$, such as "there is nothing which is outside", i.e. $\lnot \;\exists \;xO(x)$, and thus 'Nothing' never occurs as a noun or as a predicate.

What is the role of metaphysics? According to Carnap, although metaphysics has not theoretical content, it has content indeed: metaphysical pseudo-statements express the attitude of a person towards life. Metaphysics is an art like lyrical poetry. The metaphysician, instead of using the medium of art, works with the medium of the theoretical; he confuses art with science, attitude towards life with knowledge, and thus produces an unsatisfactory and inadequate work. "Metaphysicians are musicians without musical ability" (Carnap, “The Elimination of Metaphysics,” quoted in Sarkar, 30).

## Influence of the Vienna Circle

The Vienna Circle had an enormous influence on Western philosophy and especially Anglo-American philosophy, so much so that nearly all subsequent philosophers have had to come to terms in some way—either to agree or disagree, to accept or reject, or, more commonly, some combination of both acceptance and rejection—with its participants, their manifesto, and their work. It may not be too much to say that, with the exception of Plato's Academy, this was the most important and influential single study-group in the entire history of philosophy.

In 1936 British philosopher A. J. Ayer published the small book, Language, Truth, and Logic. Ayer was only 24 when he started the book and 26 when it was published, and this spread the central points of the verification program throughout the English-speaking world. This book can be said to be a gospel tract for logical positivism or logical empiricism. In that sense it was an introduction to and summary of the manifesto and goals of the Vienna Circle.

In addition, after the death of Schlick and the coming to power of the Nazis, most of the members of the Vienna Circle fled Europe; the majority of them going to America, where they became professors and thus influenced a generation or so of new students who went on, in turn, to become professors themselves. Thus propagation and investigation and criticism of the program and goals of the Vienna Circle became one of the most dominant forces in American philosophy for several decades, especially in philosophy of science, ethics, metaphysics, and study of formal systems (formal logic and formal language). Later philosophers reacted against, severely criticized, and ultimately rejected each of the points in the Vienna Circle's manifesto and program. But pronounced and sustained reaction against and criticism of something is itself evidence of the status and power of what one finds it necessary to criticize and reject.

## The Demise of the Vienna Circle

The physical demise of the Vienna Circle occurred when the members of the Circle were dispersed with coming to power of the Nazi party in Germany and its takeover of Austria. Many of the members of the Vienna Circle immigrated to the United States, where they taught in several universities. Schlick remained in Austria, but in 1936 he was shot and killed by a deranged student in the University of Vienna.

The intellectual and philosophical demise of the Vienna Circle took longer, but was even more complete and devastating. It did not take long for critics to begin to notice difficulties with the program of the logical positivists/logical empiricists. Problems were found with the verification principle, and no formulation of it was ever found that was satisfactory. Among other things, if it were made strong enough to eliminate all metaphysical statements, then it eliminated scientific laws (because those laws, such as "Water freezes at 100 degrees C," go beyond experience to make general claims about entities that have not been experienced) and mathematics. If it were made weak enough to admit such scientific law-like statements, then it would admit statements such as "Water freezes at 100 degrees Centigrade or the Absolute is unchanging."

Paradoxes of confirmation were found, such as confirmation of the proposition "All swans are white" by the examination of non-white non-swans. Nelson Goodman's problem of blue-green vs. grue-bleen predicates—with either specifiable in terms of the other—was expounded. W.V.O. Quine published his devastating essay, "Two Dogmas of Empiricism," showing that empiricism itself was faulty. The question of what acted as a "verifier" or "confirmer" arose. By 1950 Carl G. Hempel had published his essay admitting the problems with the verifiability criterion, "Problems and Changes in the Empiricist Criterion of Meaning." More and more attacks on and refutations of all the points of the Vienna Circle Manifesto piled up, with the result that every important point in that manifesto eventually became incapable of being supported by philosophers who were knowledgeable about the issues. Those attacks could succeed because the logical positivist program was explicitly and rigorously stated and used logical methods. Thus it could be directly and strictly refuted and disproved, unlike those high-flown, unspecific, and logic-wanting metaphysical systems such as presented by Hegel and Martin Heidegger.

By the 1960s, John Passmore could proclaim, "Logical positivism, then, is dead, or as dead as a philosophical movement ever becomes. But it has left a legacy."[2] It wholly failed in Germany, where Heidegger's metaphysics represented everything that the positivists opposed. Its great legacy was and continues to be in the English speaking countries and anywhere else where philosophy attended or attends to logic and language, not "the world," and where an appreciation for the logical rigor and clarity of logical positivism still persists and where skepticism about high-flown and otiose metaphysics still prevails.

Later in his life A. J. Ayer himself admitted that what he had proclaimed and championed in Language, Truth, and Logic was "all wrong."

## Congresses and publications

The Vienna Circle was very active in advertising the new philosophical ideas it championed. Several congresses on epistemology and philosophy of science were organized, with the help of the Berlin Circle. There were some preparatory congresses: Prague (1929), Königsberg (1930), Prague (1934) and then the first congress on scientific philosophy held in Paris (1935), followed by congresses in Copenhagen (1936), Paris (1937), Cambridge, UK (1938), Cambridge, Massachusetts (1939). The Königsberg congress (1930) was very important, for Kurt Gödel announced that he has proved the completeness of first order logic and the incompleteness of formal arithmetic. Another very interesting congress was the one held in Copenhagen (1936), which was dedicated to quantum physics and causality.

Between 1928 and 1937, the Vienna Circle published ten books in a collection named Schriften zur wissenschaftlichen Weltauffassung (Monographs on the Scientific World-Conception), edited by Schlick and Philipp Frank. Karl Raimund Popper’s book Logik der Forschung was published in this collection. Seven works were published in another collection, called Einheitswissenschaft (Unified Science). In 1930 Rudolf Carnap and Hans Reichenbach undertook the editorship of the journal Erkenntnis, which was published between 1930 and 1940 (from 1939 the editors were Otto Neurath, Rudolf Carnap and Charles Morris).

The following is a list of works published in the two collections edited by the Vienna Circle.

Schriften zur wissenschaftlichen Weltauffassung (Monographs on the Scientific World-Conception), edit by Schlick and Frank.

• von Mises, Richard. Wahrscheinlichkeit, Statistik und Wahrheit. 1928.Probability, Statistics, and Truth. New York: Macmillan, 1939.
• Carnap, Rudolf. Abriss der Logistik, 1929
• Schlick, Moritz. Fragen der Ethik, 1930. Problems of Ethics. New York: Prentice-Hall, 1939.
• Neurath, Otto. Empirische Soziologie, 1931.
• Frank, Philipp. Das Kausalgesetz und seine Grenzen, 1932. The Law of Causality and its Limits. Boston: Kluwer, 1997.
• Kant, Otto. Zur Biologie der Ethik, 1932.
• Carnap, Rudolf. Logische Syntax der Sprache, 1934. The Logical Syntax of Language. New York: Humanities, 1937.
• Popper, Karl. Logik der Forschung, 1934. The Logic of Scientific Discovery. New York: Basic Books, 1959.
• Schächeter, Josef. Prolegomena zu einer kritischen Grammatik, 1935. Prolegomena to a Critical Grammar. Boston: D. Reidel Pub. Co., 1973.
• Kraft, Victor. Die Grundlagen einer wissenschaftliche Wertlehre, 1937. Foundations for a Scientific Analysis of Value. Boston : D. Reidel Pub. Co., 1981.
• Einheitswissenschaft (Unified Science), edit by Carnap, Frank, Hahn, Neurath, Joergensen (after Hahn's death), Morris (from 1938):
• Hahn, Hans. Logik, Mathematik und Naturerkennen, 1933.
• Neurath, Otto. Einheitswissenschaft und Psychologie, 1933.
• Carnap, Rudolf. Die Aufgabe der Wissenschaftlogik, 1934.
• Frank, Philipp. Das Ende der mechanistischen Physik, 1935.
• Neurath, Otto. Was bedeutet rationale Wirtschaftsbetrachtung, 1935.
• Neurath, Otto, E. Brunswik, C. Hull, G. Mannoury, J. Woodger, Zur Enzyklopädie der Einheitswissenschaft. Vorträge, 1938.
• von Mises, Richard. Ernst Mach und die empiristische Wissenschaftauffassung, 1939.

These works are translated in Unified Science: The Vienna Circle Monograph Series Originally Edited by Otto Neurath, Kluwer, 1987.

Monographs, arranged in chronological order, published in the International Encyclopedia of Unified Science:

• Otto Neurath, Nils Bohr, John Dewey, Bertrand Russell, Rudolf Carnap, Charles Morris, Encyclopedia and unified science, 1938, vol.1 n.1
• Charles Morris, Foundations of the theory of signs, 1938, vol.1 n.2
• Victor Lenzen, Procedures of empirical sciences, 1938, vol.1 n.5
• Rudolf Carnap, Foundations of logic and mathematics, 1939, vol.1 n.3
• Leonard Bloomfield, Linguistic aspects of science, 1939, vol.1 n.4
• Ernest Nagel, Principles of the theory of probability, 1939, vol.1 n.6
• John Dewey, Theory of valuation, 1939, vol.2 n.4
• Giorgio De Santillana and Egdard Zilsel, The development of rationalism and empiricism, 1941, vol.2 n.8
• Otto Neurath, Foundations of social sciences, 1944, vol.2 n.1
• Joseph Henri Woodger, The technique of theory construction, 1949, vol.2 n.5
• Philipp Frank, Foundations of physics, 1946, vol.1 n.7
• Erwin Frinlay-Freundlich, Cosmology, 1951, vol.1 n.8
• Joergen Joergensen, The development of logical empiricism, 1951, vol.2 n.9
• Egon Brunswik, The conceptual framework of psychology, 1952, vol.1 n.10
• Carl Hempel, Fundamentals of concept formation in empirical science, 1952, vol.2 n.7
• Felix Mainx, Foundations of biology, 1955, vol.1 n.9
• Abraham Edel, Science and the structure of ethics, 1961, vol.2 n.3
• Thomas Kuhn, The structure of scientific revolutions, 1962, vol.2 n.2
• Gherard Tintner, Methodology of mathematical economics and econometrics, 1968, vol.2 n.6
• Herbert Feigl and Charles Morris, Bibliography and index, 1969, vol.2 n.10

## Notes

1. English translation: “The Elimination of Metaphysics Through Logical Analysis of Language” in Sohatra Sarkar (ed.). Logical empiricism at its peak: Schlick, Carnap, and Neurath. New York: Garland Pub., 1996, pp. 10-31.
2. "Logical Positivism," in The Encyclopedia of Philosophy, vol. 5, p. 56.

## References

• Carnap, Rudolf. "Überwindung der Metaphysik durch Logische Analyse der Sprache" in Erkenntnis 2 (1932). English translation: "The Elimination of Metaphysics Through Logical Analysis of Language" in Sahotra Sarkar (ed.). Logical empiricism at its peak: Schlick, Carnap, and Neurath. New York: Garland Publishing, 1996. 10-31.
• Foundations of the Unity of Sciences vol. 1. Chicago: The University of Chicago Press, 1969.
• Uebel, Thomas. "On the Austrian Roots of Logical Empiricism" in Logical Empiricism - Historical and contemporary Perspectives, ed. Paolo Parrini, Wesley C. Salmon, Merrilee H. Salmon. Pittsburgh, PA: University of Pittsburgh Press, 2003. 76-93.
• “Wissenschaftliche Weltauffassung. Der Wiener Kreis,” 1929. English translation: “The Scientific Conception of the World. The Vienna Circle” in Sahotra Sarkar (ed.). The Emergence of Logical Empiricism: from 1900 to the Vienna Circle. New York: Garland Publishing, 1996. 321-340

There is an enormous literature on the Vienna Circle, logical positivism, and logical empiricism. These are some of the main texts and some studies of the movement:

• Ayer, Alfred Jules. Language, Truth, and Logic. London: Gollanez, 1936.
• Ayer, Alfred Jules. Logical Positivism. Glencoe, Ill: Free Press, 1959.
• Barone, Francesco. Il neopositivismo logico. Roma Bari: Laterza, 1986.
• Bergmann, Gustav. The Metaphysics of Logical Positivism. New York: Longmans Green, 1954.
• Carnap, Rudolf. Der Logische Aufbau der Welt. Berlin: Welkreis-Verlag, 1928
• Cirera, Ramon. Carnap and the Vienna Circle: Empiricism and Logical Syntax. Atlanta, GA: Rodopi, 1994.
• Friedman, Michael, Reconsidering Logical Positivism. Cambridge, UK: Cambridge University Press, 1999.
• Gadol, Eugene T. Rationality and Science: A Memorial Volume for Moritz Schlick in Celebration of the Centennial of his Birth. Wien: Springer, 1982.
• Geymonat, Ludovico. La nuova filosofia della natura in Germania. Torino, 1934.
• Giere, Ronald N. and Richardson, Alan W. Origins of Logical Empiricism. Minneapolis: University of Minnesota Press, 1997.
• Kraft, Victor. The Vienna Circle: The Origin of Neo-positivism, a Chapter in the History of Recent Philosophy. New York: Greenwood Press, 1953.
• McGuinness, Brian. Wittgenstein and the Vienna Circle: Conversations Recorded by Friedrich Waismann. Trans. by Joachim Schulte and Brian McGuinness. New York: Barnes & Noble Books, 1979.
• Parrini, Paolo; Salmon, Wesley C.; Salmon, Merrilee H. (ed.) Logical Empiricism - Historical and Contemporary Perspectives, Pittsburgh: University of Pittsburgh Press, 2003.
• Rorty, Richard, ed. with Introductory Essay. The Linguistic Turn. Chicago: University of Chicago Press, 1967. (Contains important essays by Schlick, Carnap, Bergmann, and many others, plus an enormous bibliography of more than 900 items.)
• Salmon, Wesley and Wolters, Gereon (ed.), Logic, Language, and the Structure of Scientific Theories: Proceedings of the Carnap-Reichenbach Centennial, University of Konstanz, 21-24 May 1991, Pittsburgh: University of Pittsburgh Press, 1994.
• Sarkar, Sahotra. The Emergence of Logical Empiricism: From 1900 to the Vienna Circle. New York: Garland Publishing, 1996.
• Sarkar, Sahotra. Logical Empiricism at its Peak: Schlick, Carnap, and Neurath. New York: Garland Pub., 1996.
• Sarkar, Sahotra. Logical Empiricism and the Special Sciences: Reichenbach, Feigl, and Nagel. New York: Garland Pub., 1996.
• Sarkar, Sahotra. Decline and Obsolescence of Logical Empiricism: Carnap vs. Quine and the Critics. New York: Garland Pub., 1996.
• Sarkar, Sahotra. The Legacy of the Vienna Circle: Modern Reappraisals. New York: Garland Pub., 1996.
• Spohn, Wolfgang (ed.), Erkenntnis Orientated: A Centennial Volume for Rudolf Carnap and Hans Reichenbach, Boston: Kluwer Academic Publishers, 1991.