Franz Brentano

Brentano revived the medieval scholastic concept of intentionality, arguing that every mental phenomenon is characterized by directedness toward an object—every thought is a thought about something, every desire is a desire for something. He presented this as the defining criterion that distinguishes mental phenomena from physical phenomena in his 1874 work Psychology from an Empirical Standpoint.

Brentano taught Edmund Husserl at the University of Vienna, and his concept of intentionality became the conceptual foundation for Husserl's entire phenomenological project. The phenomenological tradition that grew from this influence extended through Heidegger, Sartre, and Merleau-Ponty, making Brentano one of the most consequential teachers in modern European philosophy.

Brentano developed what he called descriptive psychology, which classifies and analyzes mental acts—such as judging, feeling, and willing—through inner perception rather than laboratory experimentation. This methodological emphasis on the first-person description of conscious experience contrasted with the emerging experimental psychology of figures like Wilhelm Wundt, and it directly anticipated later developments in phenomenological method.

Brentano was forced to resign from his professorship at the University of Vienna after he renounced his Catholic priestly vows and married, which conflicted with Austrian regulations governing academic appointments for former clergy. He continued to teach and influence students privately, and his intellectual circle in Vienna remained one of the most important centers of philosophical activity in late 19th-century Europe.