To the extent that these thoughts coincide with those of R. Avenarius and E. Mach, we have no differences; I gladly agree with them. I am genuinely convinced, in particular, that we owe a vast amount of logical illumination to the historical-methodological labors of Ernst Mach, and that this is the case where one cannot fully agree with his conclusions. Mach, unfortunately, does not appear to me to have tackled what are the most fruitful problems of the economy of thought, problems I tried to formulate above in a somewhat brief but quite sufficient fashion. His failure to do this is, in any case, partly due to the epistemological misinterpretations that he thought of as necessary foundations for his investigations. Mach's writings have, however, had an immense influence with respect to these very misinterpretations. This is the side of his thought that he shares with Richard Avenarius, and it is in respect to this which I must here oppose him.