 In 1929, at Reichenbach’s suggestion, Hempel spent the fall semester at the University of Vienna, where he studied with Carnap, Moritz Schlick, and Frederick Waismann, who were advocates of logical positivism and members of (what came to be known as) “the Vienna Circle”. It would fall to Hempel to become perhaps the most astute critic of that movement and to contribute to its refinement as logical empiricism. As Hitler increased his power in Germany, Hempel, who was not Jewish but did not support the Nazi regime, moved to Brussels and began collaborating with Paul Oppenheim, which would result in several classic papers, including “Studies in the Logic of Explanation”, which appeared in 1948 (Rescher 2005: Chs. 8 and 9). Hempel would also visit the United States twice—the University of Chicago in 1937–38 and then the City College of New York in 1939–40, where he held his first academic position—and eventually became a naturalized citizen.