 By the late 1920s Reichenbach was moving away from neo-Kantian positions and towards logical positivist views, allying himself with the Vienna Circle philosophers, although he always maintained and emphasized in retrospect that the “empiricist philosophy” he pursued in the Berlin Group was much more focused and engaged with science and did not fall prey to the positivist problems that came out of attempts to ground knowledge on sense data alone. He did not view his contemporaries uniformly. For Moritz Schlick, Reichenbach seems to have had a somewhat condescending respect, for Ludwig Wittgenstein, who is one of the few philosophers whom he later criticizes by name in Experience and Prediction (1938c), and for Karl Popper, none whatsoever. Aside from Einstein, his deepest respect and closest intellectual alliances seem to have been with Kurt Lewin, Kurt Grelling, Rudolf Carnap, Richard von Mises (although they do not seem to have got along personally) and Bertrand Russell, although Reichenbach was not pleased with Russell’s criticism of his views in Russell’s last philosophical book, Human Knowledge, Its Scope and Limits (Russell, 1948; see Reichenbach 1978, vol. II, p. 405). 