Logical Positivism: What Is It, and Who Were the Vienna Circle Philosophers

Who they were, and where they met

The Vienna Circle formed in Vienna around Moritz Schlick, after his arrival in 1922.

That year the University of Vienna appointed Schlick to its chair of philosophy of the inductive sciences, a post that had belonged to Ernst Mach. The regular, weekly meetings began only in 1924, though, and ran, during the academic terms, until 1936: two distinct moments, Schlick’s arrival and the start of the meetings, two years apart. The group mixed philosophers with a scientific training and scientists with a philosophical bent: besides Schlick, it included the mathematician Hans Hahn, the physicist Philipp Frank, the social scientist Otto Neurath, the mathematician Olga Hahn-Neurath, the philosopher Viktor Kraft and, from 1926, the philosopher and logician Rudolf Carnap. Other members joined among Schlick’s students, such as Friedrich Waismann and Herbert Feigl, and among Hahn’s, such as Karl Menger and Kurt Gödel.

What counted as “meaningful”

For the Circle, a meaningful statement had to carry factual content: it had to be an analytic, a priori proposition, like those of logic and mathematics, or an empirical, synthetic proposition, verifiable through experience. The criterion could not rest on immediate practical verification alone, though: taken literally, that stricter version would have stripped meaning from many scientific hypotheses that nobody, in the daily practice of a laboratory, can check right away. The Circle’s members noticed the problem themselves, and argued about it.

On this basis the group rejected the claims to knowledge made by traditional metaphysics, since its statements fit neither the analytic a priori category nor the empirical, synthetic, verifiable one. Its members saw themselves as conceptual revolutionaries: for them metaphysics was not simply false, it was entirely without cognitive meaning, a distinction that can look subtle to a reader today but that for them marked the very boundary of knowledge.

Practical example: a sentence such as “it will rain in Vienna tomorrow” is an empirical proposition, verifiable by watching the sky the next day: for the Circle it has meaning, whether it turns out true or false. A sentence such as “the ultimate essence of reality transcends experience” cannot be verified in any way, nor is it true by definition like a theorem of logic: for the Circle it is neither true nor false, simply outside the field of what can be said with sense.

The Circle’s verification criterion sits inside a tradition going back to David Hume’s empiricism, for which knowledge of the world comes from sense experience, and it clashes with Immanuel Kant’s claim that synthetic a priori judgments exist, known independently of experience yet not purely logical: a third category the Circle refused to admit.

Wittgenstein, close but not inside

Ludwig Wittgenstein was never part of the Vienna Circle.

He discussed his ideas privately with Schlick and Waismann, on two occasions, in December 1929 and January 1930, putting forward the thesis that the sense of a proposition coincides with the method for verifying it. The group’s meetings also discussed his Tractatus, and there were several direct encounters among Wittgenstein, Schlick, Waismann and Carnap: a constant presence in the discussions, yet always outside the Circle as an institution.

The end of the Circle

The Circle did not break up for a single reason. From 1934, with antisemitism institutionalized in Austria, the Verein Ernst Mach, the association that hosted the meetings, was shut down for political reasons. After Schlick’s killing in 1936, by a student sympathetic to Nazism at the University of Vienna, only a small remaining group managed to keep meeting in Vienna for two more years, while the other members had already scattered into emigration and forced exile, many of them toward the United States.

Logical positivism and Comte’s Positivism: two currents, not one

The name “positivism” recurs at two distinct moments in philosophy, and it is worth telling them apart, as the Recap on Auguste Comte’s Positivism and the reactions it provoked also does. Over the twentieth century, Comte’s original, nineteenth-century positivism was largely forgotten, overshadowed by neopositivism, that is, by the Vienna Circle’s logical positivism. The twentieth-century critiques of Thomas Kuhn and Paul Feyerabend, which gave rise to so-called “post-positivism,” targeted Carnap’s neopositivism: the nineteenth-century Comte stayed outside that target, even though later commentators have often mixed the two up.

Readers who want to trace the scientific method the Circle looked to can find its roots in Galileo Galilei’s scientific revolution and in the debate on the theory of knowledge opened by Kant’s Critique of Pure Reason.