Logical Empiricism

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Logical empiricism (LE) is a term that was coined by the Austrian sociologist and economist Otto Neurath (1880–1945) to name the philosophical work of the Vienna Circle and related work being pursued by the physicist and philosopher Hans Reichenbach (1891–1953) and his associates. Related terms include logical positivism, neopositivism, and scientific empiricism. The basic intention of LE was to formulate a scientific philosophy for understanding the relationship between science and society. In historico-philosophical terms the aim was to combine the empiricist legacy of philosopher-scientists such as Hermann von Helmholtz (1821–1894), Ernst Mach (1838–1916), Henri Poincaré (1854–1912), and Pierre Duhem (1861–1916), with the new logic developed by Gottlob Frege (1848–1925), David Hilbert (1862–1943), and Bertrand Russell (1872–1970). The intended synthesis was not simply a theoretical project. Logical empiricists considered themselves part of a progressist movement for a more rational and enlightened society. As stated in the so-called Manifesto of the Vienna Circle, LE aimed to foster a "scientific world-conception" ("wissenschaftliche Weltauffassung") that would help create a better world for all people.

The Scientific World-Conception

The characteristic method of LE was logical analysis, which used mathematical logic to clarify the logical structure and meaning of assertions. In this way LE aimed for a logical analysis of scientific and philosophical language that would distinguish clearly between meaningful and meaningless sentences; fight against metaphysics, which was considered as a hotbed of meaningless "pseudo-sentences"; and provide a "unified science" (Einheitswissenschaft) that would be formulated in a logically analysed language cleansed of metaphysical elements.

LE claimed that logical analysis demonstrated that there are only two kinds of meaningful propositions, the analytic a priori propositions of logic and mathematics and the synthetica posteriori propositions of empirical sciences. All other assertions were to be considered cognitively meaningless. This holds in particular for all metaphysical propositions. The most famous argument to this effect is found in "Overcoming Metaphysics by Logical Analysis of Language" 1932 by Rudolf Carnap (1891–1970). Moreover, "overcoming metaphysics" was not simply an internal philosophical issue because logical empiricists considered metaphysics to be a medium for propagating politically and morally pernicious ideologies that had to be fought not only in the academic sphere but also in the political arena.

Politically, most logical empiricists were democratic socialists or unorthodox Marxists and thus were partisans of an "engaged scientific philosophy." A few, such as Moritz Schlick (1882–1936) and Friedrich Waismann (1896–1959), were less political but shared a progressive, liberal outlook.

For all logical empiricists scientific philosophy was a collective enterprise that had to contribute to the construction of a modern, enlightened society. That task was to be carried out in close collaboration with the sciences and other progressive cultural forces, such as the artists and architects belonging to the Neue Sachlichkeit movement or the Bauhaus. When LE was at its peak in the late 1920s and early 1930s, the more radical logical empiricists of the Vienna Circle, such as Neurath and Carnap, regarded themselves as "social engineers" engaged in the task of forging the philosophical and scientific tools for building a new socialist society. This is expressed emphatically in the concluding lines of the Manifesto of the Vienna Circle: "We witness the spirit of the scientific world-conception penetrating in growing measure the forms of personal and public life, in education, upbringing, architecture, and the shaping of economic and social life according to rational principles. The scientific world-conception serves life, and life receives it" (Sarkar 1996, Vol. I, pp. 329–330).

LE included a multifaceted and variegated group of philosophers and scientists. Its internal diversity often is underestimated. LE was less a school with a common doctrine than a movement whose members shared vaguely progressist convictions. Even closely related thinkers such as Carnap and Neurath disagreed on many basic philosophical issues. Here the focus is on few leading figures of the Vienna Circle: Schlick, its founder; Carnap and Neurath; and Carl Gustav Hempel (1905–1997), the most influential representative of LE in the United States.

In the early 1930s the LE movement in Europe gradually dissipated as a result of disastrous, political developments and indivdual events. The mathematician Hans Hahn (1879–1934), considered by some to be the "real" founder of the Vienna Circle, died in 1934, and Schlick was murdered by a demented student in 1936. In 1934 Carnap left Vienna and moved to the German university in Prague. After the rise of National Socialism in Germany (1933) and clerical fascism in Austria (1934) most logical empiricists emigrated. The majority went to the United States, including Carnap, Reichenbach, and Hempel. The history of LE thus divided into two periods: a European period ending in the mid-1930s and an Anglo-American period from the 1930s until its dissipation in the 1960s.

Major Figures and Their Ideas

The founder and official leader of the Vienna Circle was Schlick, who studied physics under Max Planck (1858–1947). Later Schlick turned to philosophy, and in 1922 he was appointed to the chair of natural philosophy at the University of Vienna as the sucessor to Ludwig Boltzmann (1844–1906) and Ernst Mach (1838–1916). Beginning in 1923, he and his assistants Herbert Feigl (1902–1988) and Friedrich Waismann organized a discussion group (first called the "Schlick circle") that soon became known as the "Vienna Circle."

Schlick had begun as a "critical realist", and later was influenced by Ludwig Wittgenstein (1889–1951). In The Turning-Point in Philosophy (1930) Schlick emphatically endorsed Wittgenstein's thesis that the philosophy of science is not to be considered a system of knowledge but instead a system of acts: "[P]hilosophy ... is that activity whereby the meaning of statements is established or discovered. Philosophy elucidates propositions, science verifies them" (Sakar 1996, vol. II, p. 5). This entailed the idea that only propositions that are meaningful can be verified. Philosophy, as philosophy of science, thus is left with the task of explaining what is meant by verification. Following Wittgenstein, Schlick proposed that the meaning of a proposition is established by its method of verification, that is, method for determining whether it is true or false. Formulated negatively, a proposition for which no verification procedure can be imagined is a meaningless pseudo-sentence.

The principle of verifiability initially appears to be quite plausible. However, it turns, out to be impossible to construct a definition that would classify all the statements of empirical science as meaningful while disqualifying all metaphysical assertions as meaningless. Even if it was easy to formulate criteria that rendered meaningful observational statements such as "it is cold outside now," it turned out to be extremely difficult to distinguish in a principled manner meaningful scientific statements such as "all electrons have the same charge" or "f = ma" from meaningless metaphysical pseudo-statements such as "the absolute is perfect".

Probably the best-known representative of LE is Carnap; there is even a misleading tendency to identify LE with Carnap's philosophy. Carnap began his philosophical career as a neo-Kantian with The Logical Structure of the World (Der Logische Aufbau der Welt) (1928), which proposed constitutional theory as a scientific successor to traditional epistemology and philosophy of science. Constitutional theory was to be a general theory of rational reconstruction of scientific knowledge in the logico-mathematical framework of Alfred North Whitehead (1861–1947) and Bertrand Russell's (1872–1970) Principia Mathematica. In informal terms the constitution of a concept provides coordinates that determine its logical place in a conceptual system.

Subsequently, Carnap replaced constitutional systems with more empiricist constitutional languages and pursued the philosophy of science as the study of the structure of the languages of science. According to Carnap, the task of philosophy is to construct linguistic and ontological frameworks that can be used in the ongoing progress of scientific knowledge. In Testability and Meaning (1937) he argued that philosophy should not formulate its principles as assertions such as "All knowledge is empirical" or "All synthetic sentences that we can know are based on experiences" or the like—but rather in the form of a proposal or requirement. By such a formulation, he maintained, "greater clarity will be gained both for carrying on discussion between empiricists and anti-empiricists as well as for the reflections of empiricists" (Sakar 1996, Vol. II, p. 258). Throughout his philosophical career Carnap saw the task of logical empiricist philosophy of science as formulating a general theory of linguistic frameworks to provide conceptual tools for the enhancement of science and philosophy, as already had been done implicitly in the 1929 manifesto.

The sociologist, economist, and philosopher Neurath was the most radically "engaged philosopher" in the Vienna Circle. He was the driving force behind the rapid change from an academic discussion group to an international philosophical movement that eventually was to dominate the philosophy of science in the mid-twentieth century. A pitiless fighter against traditional metaphysics, Neurath made his most important positive contribution to the scientific world-conception in the form of the project of "unified science."

In contrast to the essentially negative program of eliminating metaphysics, the project for a unified science is the great constructive paradigm of LE. According to Neurath, scientific knowledge does not have the form of an all-embracing deductive system but constitutes an encyclopedia. According to encyclopedism, as he termed his account, scientific knowledge has the following five characteristics: It is fallible, pluralistic, holistic, and locally but not globally systematizable, and it is not an image of the real world. Neurath conceived the encyclopedistic project as a large-scale politico-scientific and philosophical program aimed at the highest possible level of the integration of the sciences without succumbing to the temptation of an exaggerated rationalism that would force the sciences into the straihtjacket of a metaphysical system.

The foundation for Neurath's encyclopedism was a robust physicalism according to which all concepts can be defined ultimately and entirely in terms of physicalist concepts and/or the concepts of logic and mathematics. Physicalist concepts are not simply the concepts of physics but instead are the concepts of everyday language dealing with middle-sized spatio-temporally located things and processes. Physicalist language, cleansed of metaphysical phrases and enriched by scientific concepts, was conceived as a mixed language containing precise and vague terms side by side. Depending essentially on the concrete practices of everyday life, Neurath's encyclopedism turned scientific knowledge into historically and socially situated knowledge. This had strong implications for its form. Instead of the "pseudorationalist" conception of a timeless objective "system" of knowledge that would create a picture of the world "as it really is," Neurath put forth a more flexible, non-hierarchical encyclopedia as the appropriate model for human knowledge.

Although Neurath's account of LE is the version most congenial to science, technology, and social studies, this has not been recognized widely. One reason for this misunderstanding is Neurath's death in 1945, which made it impossible to promote his version of LE in the Anglo-American world. Since the 1980s, however, Neurath's vision has received a considerable reconsideration in both the United States and Europe.

Carl Gustav Hempel was Reichenbach's student in Berlin but also spent time in Vienna. After emigrating to the United States via Belgium he became Carnap's assistant in 1937. He began his philosophical career with a dissertation on the logical analysis of the concept of probability. In the 1950s and 1960s he became the most influential logical empiricist in the English-speaking philosophical community. His papers set a standard for the logical analysis of concepts. For instance, his contributions to the theory of scientific confirmation and explanation, especially the covering-law model, determined the agenda of analytic philosophy of science for decades. His "Fundamentals of Concepts Formation in Empirical Science" (1952) served as an introduction to philosophy of science for generations of students.

Hempel was particularly engaged in pointing out difficulties and paradoxical features in many core concepts of the philosophy of science, arguing for the necessity of a thoroughgoing logical analysis. The "raven paradox" is a famous example: If it is a law of nature that all ravens are black, the observation of a black raven may count as a (partial) confirmation of this law. Moreover, it is reasonable to assume that laws of nature should be independent of their logical formulation. Thus, the law that all ravens are black has the logical form "All R are B," which is logically equivalent to "All non-B are non-R." With this conceded, a green frog, as something that is not black and not a raven, counts as a (partial) confirmation of the original law. However, this is absurd. Hence, something in the conception of natural law and confirmation seems to be wrong. The raven paradox shows that philosophers do not understand even the most basic concepts in the philosophy of science fully.

Hempel's philosophical work was characterized by a careful and circumspect application of modern logic that made the achievements of logical analysis attractive even for those who were not professional logicians and philosophers. For instance, The Function of General Laws in History (1942) exerted influence far beyond the confines of philosophy. It is one of the few LE analyses that has had an impact in the humanities. In Problems and Changes in the Empiricist Criterion of Meaning (1950) Hempel further criticized the various logical empiricist attempts to formulate a waterproof criterion for distinguishing meaningful and meaningless assertions. In later years Hempel was influenced by Thomas Kuhn (1922–1996), belying the claim that LE and historical accounts of science are necessarily opposed.


A special problem in LE is the transformation of the movement when the intellectual exodus from Europe to the United States took place in the 1930s. The transplantation of LE did not leave its philosophical content unaffected. Although a comprehensive history of LE has not been written, important differences between the two versions can be noted easily. European LE was politically much more radical than its U.S. successor. Although the Vienna Circle showed a vigorous interest in political and social issues such as education, technology, architecture, and art, in the United States the political dimension of LE became less visible. For instance, Carnap was a dedidated supporter of the civil rights movement until the end of his life.

One factor in this change from a radically "engaged scientific philosophy" to an academically confined "philosophy of science" is surely the fact that logica empiricists had to adapt to a different political and societal context in which the application of their traditional political categories was difficult. Another reason may have been that to survive in exile it was expedient to use a language that was more cautious than that which was acceptable in the "Red Vienna" of the late 1920s. After all, LE started in the United States among a rather obscure philosophical group of emigrants without much of a reputation. Only gradually did it become the mainstream in Anglo-American philosophy of science and epistemology in the 1940s and 1950s.

The dominance of LE did not last long, however. First, many of the internal problems of the movement, such as the issue of distinguishing neatly between meaningful and meaningless statements, stubbornly resisted a satisfying solution. Second, analytic philosophers such as Willard van Orman Quine (1908–2000) and Hilary Putnam (b. 1926) attacked the very basis of the logical empiricist philosophy of science, that is, the distinction between the synthetic/analytic and the observational/theoretical levels of empirical knowledge. Third, authors such as Norwood Russell Hanson (1924–1967) and Thomas Kuhn (1922–1996) shifted the emphasis from the strictly logical toward the historical and sociological aspects of scientific theorizing, thus challenging the autonomy of a logical philosophy of science in the style of Carnap.

In a sense these and related developments were welcomed as liberations from the straitjacket of the so-called "received view." For instance, one immediate consequence of the logical empiricist thesis that meaningful statements are either analytic or empirical was that all value judgments are cognitively meaningless. Value statements are not analytic because they say nothing about the world and are not empirical because they cannot be verified. Hence, they are meaningless. The dichotomy between analytic and empirical statements led logical empiricists to a strictly noncognitivist (emotivist) ethics according to which there can be no knowledge of values in a proper sense. This stance is not to be considered as necessarily leading to a loss of interest in moral and political problems. All members of the Vienna Circle took a strong interest in the political and social events they were living through. These problems, however, were considered as practical problems, to be strictly separated from the theoretical problems science and philosophy were dealing with.

This emotivist account of ethics, which leaves only a small niche for "theoretical meta-ethics," that is, the logical analysis of moral statements, is insufficient. In a world in which science and technology present increasing numbers of ethical questions and difficulties, it does not provide reasoned arguments formorally relevant actions.

At the same time the complete dismissal of LE by the self-proclaimed "revolutionary" postpositivist philosophy of science might have been a bit hasty, especially if one takes into account its lesser-known European variants. Indeed, the differences between LE and postpositivist philosophy of science might have been unfairly exaggerated. With regard to Neurath's and Hempel's versions of LE, it does not seem far-fetched to suggest that to some extent the allegedly unbridgeable gap between LE and its successors has been an interest-guided social construction. As usual, the critics of LE were unaware of how much they had absorbed of the belief system they so eagerly berated.

In summary, one may propose that LE was a rich philosophical movement that set the stage for a large part of the philosophy of science and epistemology during the twentieth century. However, despite this general claim, a balanced assessment of the movement has not been formulated. In particular, the relationships between LE and its successor disciplines, such as the various currents of "postpositivist" philosophy of science, cultural studies of science, and science, technology, and society studies (STS), are not yet fully appreciated.


SEE ALSO German Perspectives;Science, Technology, and Society Studies;Wittgenstein, Ludwig.


Carnap, Rudolf. (1967 [1928]). The Logical Structure of the World. Berkeley and Los Angeles: University of California Press. Basic work of logical empiricism of the Vienna Circle.

Carnap, Rudolf. (1937). The Logical Syntax of Language. London: Routledge and Kegan Paul. Basic work of logical empiricism.

Friedman, Michael. (1999). Reconsidering Logical Positivism. Cambridge, UK: Cambridge University Press. Collection of trail-blazing essays for the recent re-evaluation of logical empiricism, particularly Carnap's philosophy.

Giere, Ronald N., and Alan W. Richardson, eds. (1996). Origins of Logical Empiricism. Minnesota Studies in the Philosophy of Science XVI. Minneapolis and London: University of Minnesota Press.

Hempel, Carl Gustav. (2000). Selected Philosophical Essays, ed. Richard Jeffrey. Cambridge, UK: Cambridge University Press.

Kuhn, Thomas S. (1970). The Structure of Scientific Revolutions. Chicago: Chicago University Press. Basic work of post-empiricist philosophy of science.

Neurath, Otto. (1981). Gesammelte philosophische und methodologische Schriften, 2 vols., ed. Rudolf Haller and Heiner Rutte. Vienna: Hölder-Pichler-Tempsky. Collected philosophical and methodological works of Neurath.

Sakar, Sahotra. (1996). Science and Philosophy in the Twentieth Century: Basic Works of Logical Empiricism, 6 vols. New York and London: Garland. Six volumes of reprints of the classic papers of logical empiricism and related currents of philosophy.

Stadler, Friedrich. (2001). The Vienna Circle: Studies in the Origins, Developments, and Influence of Logical Empiricism. Vienna and New York: Springer. Provides the most complete account of logical empiricism in Europe.