Positivism

The most developed form of positivism was the logical positivism or logical empiricism (LE) of the Vienna Circle. LE developed in three main phases: the first Vienna Circle from about 1907; the second Vienna Circle (the Vienna Circle proper), from the mid-1920s until about 1933; and the predominantly American emigrant phase after Hitler came to power. In all three cases the logical empiricists (LEs) were scientists, mathematicians, and scientifically trained philosophers who met to discuss substantive and methodological problems of science and society. The first circle was influenced directly by Mach and other scientists such as Heinrich Hertz, Richard Avenarius, Wilhelm Ostwald, Henri Poincaré, and Pierre Duhem, and by scientific developments such as non-Euclidean geometry, David Hilbert's axiomatization of Euclidean geometry, and Einstein's relativity theories. The second circle was heavily influenced additionally by Bertrand Russell and Alfred North Whitehead's attempted reduction of mathematics to the new symbolic logic in Principia Mathematica (1910–1913), Ludwig Wittgenstein's Tractatus (1921), Hilbert's metamathematics, the new quantum theory, behavioral psychology, and antivitalistic progress in biology.

All three phases were also shaped by their respective social contexts. The first circle experienced the events leading to World War I and the final days of the Habsburg Empire, while the Weimar period framed the sociopolitical issues of the second circle. By contrast, the "end of ideology" characterized the American period, especially after World War II. Upon the emigration to America by members of the circle, the LE social program vanished. The American LEs presented their work as purely technical and hence politically neutral.

Many postmodern intellectuals, who think of the positivists as heavy-handed, dogmatic conservatives or as emotionless technical analysts disinterested in cultural affairs, are surprised to learn that the Vienna Circle assigned itself the urgent mission of reforming and transforming all of social and political culture by adapting to present conditions the program of the scientific Enlightenment. A major initiative was linguistic reform. The Viennese positivists' animus against metaphysics was directed as much against obfuscatory and potentially totalitarian political discourse as it was against woolly philosophy. This is apparent at once in the manifesto of 1929, "The Scientific Conception of the World: The Vienna Circle," by Hans Hahn, Carnap, and Otto Neurath in honor of their leader, Moritz Schlick. Modernist in outlook, the Vienna Circle celebrated the machine age and the transformative reconstruction (Aufbau) of Europe after World War I. It had close ties with a similar circle of scientific philosophers around Hans Reichenbach (Einstein's colleague) in Berlin and with the Bauhaus school of design at Dessau, which in its own way emphasized clarity of structure shorn of all baroque, metaphysical adornment. Like the Bauhaus, the circle was international in outlook and pro–working class, and some members were politically active. Neurath was a neo-Marxist social scientist who radicalized the young Carnap, a logician. Schlick led a moderate wing.

When Schlick was assassinated in 1936, Neurath and Carnap became the leaders of the circle. It was in America that the indefatigable Neurath found a publisher for his dream project of a new, systematic encyclopedia of the sciences, but the overall project was a failure. Neurath died in 1945, and the University of Chicago Press published only twenty monographs of what was intended to be a long-term monthly subscription series. (These were later reissued as the two volumes of Foundations of the Unity of Science in 1955 and 1970.) One of the last contributions was Thomas Kuhn's Structure of Scientific Revolutions (1962), commonly regarded as a refutation of logical empiricism. Meanwhile, Carnap, Herbert Feigl, Reichenbach, and Carl Hempel (a student of Reichenbach) headed the American phase of the movement. Ernest Nagel, although of a more Deweyan pragmatic cast, was a close associate. In America, unlike Europe, the aforementioned all had important academic positions, which they used to found the new specialty discipline of philosophy of science as well as to teach a new generation of philosophers, including Adolf Grünbaum, Wesley Salmon, and Hilary Putnam. With its rigorous formal methods, LE made the pragmatism of Charles Peirce, William James, and John Dewey seem quaintly dated and gradually displaced it as the official scientific philosophy. LE remained dominant until the 1960s and still casts a large shadow at the start of the twenty-first century.

The received view of the Vienna Circle is largely a post-Kuhnian construction that is now being contested. To be sure, the LEs wanted to make philosophy (or their replacement for it) a collective, progressive enterprise like that of the sciences, but the manifesto announced a more iconoclastic unity than was actually present. Accordingly, it was easy for opponents to miss the internal discord and tar all LEs with the same brush. Although the LEs were vehemently antimetaphysical and rejected most philosophy as a meaningless, fruitless pursuit of solutions to "pseudoproblems," they were liberal in refusing to dogmatize about empirical questions and they viewed their group as open to discussion of all views. Another source of misunderstanding was A. J. Ayer's inflammatory Language, Truth, and Logic (1936), the book that brought German positivism to an English-speaking audience. Ayer's "potboiler" (as it has been called) mis-located the positivists in the British empiricist tradition.

Archival research sensitive to the intellectual and cultural milieu of central Europe later provided a major reinterpretation of the Austro-German positivist movement from Mach to Hempel. The participants came from varying academic backgrounds and life experiences and they frequently disagreed over matters of philosophical content as well as strategy and politics. They were their own most trenchant critics. For example, Kurt Gödel defended a Platonist (and hence metaphysical) ontology of mathematics. Neurath was out of sympathy with Carnap's project to reconstruct science within a formal logical system and with Schlick's commitment to the correspondence theory of truth. Neurath rejected the foundational, linear empiricist theory of justification, from supposedly infallible basic statements up through ever-higher levels of theory, in favor of a holistic coherence position featuring mutual support, a stance that he famously articulated in his ship metaphor: "There is no tabula rasa. We are like sailors who have to rebuild their ship on the open sea, without ever being able to dismantle it in drydock and reconstruct it from the best components" (Giere and Richardson, p. 83).

The LEs also disagreed over labels. Several members attacked "positivism," and Reichenbach sometimes denied that he was a "logical empiricist." (By the beginning of the twenty-first century, however, the inclusive term "logical empiricism" was commonly applied to both the Vienna and Berlin groups as well as the American contingent and was preferred to "logical positivism.") Also, the views of the leading figures developed significantly over their lifetimes. Accordingly, a summary that is both brief and accurate is impossible.

Contrary to Ayer, the LEs had too serious an engagement with Kant to be squarely in the British empiricist tradition. They were anti-Kantian up to a point, with the political goal of displacing the neo-Kantians of the Marburg school (which included Ernst Cassirer) as the dominant school of scientific philosophy in Europe. The central problem was to retain what was correct in Kant's critique of crude, British empiricism without commitment to Kant's permanent categories and forms of intuition, which licensed synthetic a priori judgments. The latter are necessary truths that are knowable a priori yet make substantive statements about the universe, for example, that physical space is Euclidean and the laws of mechanics, Newtonian. Without them, Kant had said, mathematics and natural science would be impossible.

Kant had realized that sensory inputs do not automatically sort themselves into intelligible perceptions about which we can make coherent judgments. Coherent perception and thought must be actively constituted by the human mind by means of its processing rules (the categories and forms of intuition). Upon analyzing relativity theory, Reichenbach and Schlick concluded that Kant was partly right: science does need constitutive framework principles that are neither logical truths nor empirical claims subject to testing and in that sense a priori. But how, then, to avoid Kant's commitment to a special, nonnatural intuition that yields synthetic a priori truths? Briefly, the LEs' solution, anticipating Kuhn's paradigms by several decades, was to disambiguate Kant's necessary a priori from the constitutive a priori of framework principles and to regard the latter as based on human convention rather than Kantian intuition. For example, Reichenbach's analysis of space-time theory bifurcated it into two components: a purely conventional component of "coordinating definitions" that define the meaning of measurement operations (and that we could change if it proved convenient to do so), plus a purely empirical component expressing the substantive content of the theory relative to the constitutive framework.

Stated in another way, the LEs' problem was how to wed empiricism to logic and mathematics. As Kant had emphasized, raw experience is not the sort of thing that can enter into logical relations with statements, providing justificatory reasons or evidence. And analytic claims need their own special warrant. Carnap, the most influential LE, later widened the above approach to include logic itself. The axioms of a logical system are not self-evident to reason, he said, for there is no such thing as a special faculty of rational intuition. It is not even a question of epistemic correctness; rather, it is a question of human linguistic convention—choice of language. The choice is pragmatic, not epistemic. We may freely choose any formal system we like and explore its consequences, keeping those systems that produce the most fruitful consequences for our purposes. Thus we arrive at the mature LE view that all and only empirical statements are synthetic and all and only a priori statements are analytic (in the pragmatically grounded sense). On this view, the a priori–a posteriori distinction coincides with the analytic-synthetic distinction. There is no synthetic a priori.

Where does philosophy fit into this scheme? For Carnap its task is purely analytic—Wissenschaftslogik, the logical analysis of the language of science using the tools of symbolic logic. Scientific philosophers clarify the logical structure of empirical science but do not do empirical science. Thus was born both mature analytic philosophy and philosophy of science as a specialty.