Conventions of measurement in psychophysics: von Kries on the so-called psychophysical law

A translation of von Krie's (1882) paper "On the measurement of intensive magnitudes and on the so-called psychophysical law" is accompanied by a commentary. Von Kries claims that intensive magnitudes are not measurable in themselves, because the establishment of an equivalence between different steps in a scale of intensity does not make any sense without further clarification. Where intensive magnitudes are determined in a domain of the natural sciences, he claims this is only a matter of counting, and of the measurement of temporal and spatial magnitudes. Every measurement of intensity should then be reduced to these operations by explicit conventions. Likewise, we can only speak of the measurement of sensations once we have established an arbitrary convention that determines what we will consider equal. The debate whether sensation varies with the logarithm of stimulus intensity or in direct proportion to stimulus intensity, is then not a difference over matters of fact. Instead it is an empty dispute over words that is rooted in misunderstanding.