Measuring the mind: The French debate on Fechner’s psychophysics in the late 19th century

The “deed of foundation” of psychophysics is notoriously identified with the publication of Fechner’s Elements of psychophysics (1860), where the project of determining, on mathematical bases, the relationship between outer excitements and inner sensations took form and led to what has been defined as the “quantitative revolution” in psychology. Yet, such a project was both a pioneering and a persnickety one. Indeed, while the possibility of treating sensations in terms of quantities and magnitudes appeared to some thinkers as a step forward in the scientific appraisal of psychic phenomena, it seemed to others undermined by several problematic implications. The aim of this paper is to assess the theoretical consequences of this project of mathematization of the mind by relying on a specific debate, namely, the late 19th-century French debate on psychophysics. Although this discipline was attacked by thinkers and scientists from all over the world, the French discussion seems to display a peculiarity: a profound concern about the reduction of internal facts to quantities and mathematical unities—in other words, the quantification of the mind. A similar worry can be grasped in both the scientific and the philosophical-academical environment, which appears to prove the existence of a common front regarding what form psychology should acquire once it had attained its scientific status.