Charles Sanders Peirce was acknowledged by William James as the founder of pragmatism; however, while James’ appreciation for psychology is well taken into account in his philosophy, the role that psychological inquiry played in Peirce’s thought remains largely unexplored. Few excellent studies indicate Peirce as the first American experimental psychologist (Cadwallader 1974, 1975; Fisch 1986) and as the first to perform a truly modern experiment in psycho-physics (Hacking 1988). Nonetheless, Peirce’s commitment to psycho-physics fails to be fully integrated with the (...) broader project of his philosophy. This integration is crucial to gain a better understanding of the complexity of Peirce’s system of thought and of his position in the psychologistic-antipsychologistic divide. On the logical side, making Peirce’s position on psychology explicit leads to investigating his material logic; on the psychological side, Peirce’s scientific approach to psychology has its theoretical foundation in Kant and further marks the distinction between Peirce’s pragmatism and James’. (shrink)