From 1924 onwards a group had begun to meet regularly around the physicist Moritz Schlick in a small room of the mathematics colloquium on Boltzmanngasse at the University of Vienna. Its core was the logician Rudolf Carnap, the sociologist-economist Otto Neurath, the mathematician Hans Hahn, the mathematician-logician Kurt Gödel, the physicist Philipp Frank, Friedrich Waismann, Herbert Feigl, and Karl Menger. Their shared touchstones were Wittgenstein's 1921 Tractatus Logico-Philosophicus, Russell and Whitehead's Principia Mathematica, Einstein's relativity, and the positivist legacy of Ernst Mach. The line between philosophy and science was dissolving: Hahn worked on mathematics, Neurath on social theory, Carnap on logic — but they were all looking for the same ground, verifiable knowledge.

In October 1929 Carnap, Hahn, and Neurath made the programme public in a small pamphlet, Wissenschaftliche Weltauffassung: Der Wiener Kreis (The Scientific World-Conception: The Vienna Circle). The text was dedicated to Schlick and put forward three core claims. First, every meaningful proposition had to be either analytic — logical or mathematical — or synthetic and empirically verifiable; if it was neither, like Hegel's 'absolute spirit' or Heidegger's 'the nothing itself nothings,' it was simply meaningless. Second, all the sciences could in principle be unified in a single logical language, the project of 'unified science.' Third, the task of philosophy was not to produce new truths but to perform the logical analysis of scientific propositions.

The public stance was deliberately combative. The manifesto explicitly claimed Vienna's nineteenth-century positivist tradition (Mach, Boltzmann), the scientific spirit of the Enlightenment, and a liberal-socialist reformism — and opposed itself to metaphysical philosophy, theology, and the rising racial-mystical currents of the period. Neurath was also one of the intellectual figures behind Vienna's famous municipal socialism. The Circle was not just an academic school but a public Enlightenment project.

That very openness sealed its fate. In 1936 Schlick was shot dead on the university staircase by a former doctoral student, and the 1938 Anschluss scattered the group: Carnap to Chicago, Neurath to Oxford, Gödel to Princeton, Feigl to Minneapolis. Yet it was precisely this exile that turned logical positivism into a cornerstone of the new analytic philosophy on the other side of the Atlantic. Hempel's theory of scientific explanation, Quine's devastating 1951 critique, Popper's falsificationism (an outsider friend-critic), and eventually Kuhn's 1962 Structure of Scientific Revolutions were all written by working through this small pamphlet. It is the founding document of twentieth-century philosophy of science.