Expands a little on Carnap’s well-known but brief account of his switch from physics to philosophy in Jena (p. 11 of the autobiography in the Schilpp volume).  On other occasions (e.g. in his reply to Ricketts, p. 281 of Reading Putnam), Putnam sometimes argues from the authority of personal acquaintance that some position or another “is just not the Carnap I knew and loved,” but in this case he’s merely telling the story, without editorializing, and it sounds authentic (to me, anyway).  Note the parallel between Carnap’s attitude toward his ponderously authoritative professor and toward the ignorant peasant to whom he compares Esperanto disparagers — both pronounce with portentous confidence on matters of which they know nothing.