This paper aims to present and evaluate Brentano’s account of the individuation of mental acts. In his early works, Brentano assimilated mental acts to tropes; however, he encountered difficulties in explaining their individuation, since the usual solutions for the individuation of tropes were not readily applicable to his theory of mental acts. In a later period, Brentano introduced into his psychology what he called the “soul”, and this allowed him to explain the individuation of mental acts. Finally, after his “reistic” (...) turn, he excluded mental acts from his ontology, for he rejected abstracta of any kind, including abstract particulars, and admitted only things, or res (in Latin), that is, concrete particulars; in his late philosophy, there are no “thinkings”, but only “thinkers”. However, he still needed to explain what individuates different thinkers, and this was again the soul. In the conclusion, the paper critically compares the different theoretical options considered by Brentano. (shrink)