The present article aims at tracing Moritz Schlick's theoretical route from 1915 to 1936 – the year he was assassinated. The authors describe this route as Schlick's attempt at successively evading what one could define as two flaws in modern philosophy – the Charybdis of Kantian epistemology and the Scylla of radical conventionalism. Such an original and daring guideline also deviates from all great epistemological philosophies dating from the beginning of the century with which the Vienna Circle's founder engaged in fruitful dialogue – among which Neokantianism and phenomenology, as well as Hilbertian Axiomatic or Poincaré and Duhem's doctrines.