In the end of the nineteenth century, there was a remarkable ‘empiricist attitude’ found among certain philosopher-scientists, an attitude which arguably emerged in the main as a reaction to the anti-scientific mood prevalent in the culture that time. Those philosopher-scientists, such as Mach and Hertz, were particularly anxious to emphasize and laud the privileged status of the empirical dimension ofour scientific knowledge, distinguishing it carefully from the theoretical constructions and hypothetical entities that are ordinarily posited by scientists. Yet, as I (...) exhibit in this article, there were certain crucial philosophical differences between these two thinkers with respect to their general conception of scientific theories and scientific norms guiding the activity. I suggest further that the most central difference in this context between Mach and Hertz can justifiably (and, perhaps, more fruitfully) be articulated and reckoned in traditional andcontemporary epistemological terms. (shrink)