Carl Friedrich Stumpf (1848–1936) met Franz Brentano for the first time on July 14, 1866, during Brentano’s defense of his habilitation thesis at the University of Würzburg. The deep impression that Brentano’s disputatio left on the young Stumpf encouraged him to attend Brentano’s lectures in the next semester and then to undertake studies in philosophy. Brentano and Hermann Lotze, who supervised Stumpf’s doctoral dissertation on Plato (Stumpf 1869) and his habilitation thesis on mathematical axioms (Stumpf 2008), are the two main sources of Stumpf’s philosophy (see Fisette 2015a, 2015b, 2015c).