[The concept of intensity in Charles Bonnet's psychology].

The concepts of intensity and vivacity are studied in the psychological texts of Charles Bonnet (1720-1793). In 1854, intensity measured physical movements of the nerves, and vivacity pertained to psychical order. In 1760, however, the two scales were confused. This development, based on an imaginary of measure justified by methodological considerations, led to a research field whose apparent goal was to measure the soul's faculties. Moreover, intensity--which had been quantified in Bouguer's work at that time (1760)--was abandoned and was transferred to the notion of energy, not yet quantified. Consequently, Bonnet's apparent dualism seems, in fact, to have been grounded on a monistic foundation, assuring an unmeasurable place to the soul, corresponding to freedom.