The physicist, psychophysicist, physician, and philosopher Gustav Theodor Fechner – an intellectual force occupying Mahler from his student years in Vienna through the composition of Das Lied von der Erde – is often described as a “mystic” or a “speculative thinker” whose fantastical philosophical system attempts to reconcile mechanistic science with an “animistic non-rational world-view.” Accordingly, his theories are usually dismissed today as curiosities. But though Fechner’s views may appear strange, on closer examination they are not mere arbitrary convictions; rather, they have a rational foundation. Furthermore, it can be demonstrated that Fechner, unorthodox thoughts notwithstanding, made important contributions to the natural sciences: particularly in the notions of “psychophysical parallelism” of the “day view,” a response to contemporaneous materialist and mechanistic orientations. The basic details of these Fechnerian ideas are presented here, along with an account of his early reception.