In this seminar we will study the various ways in which psychology, phenomenology and metaphysics are intertwined in Frans Brentano’s philosophy. By a close reading of many brentanians texts—from the early works on Aristotle (On the manifold meanings of Being in Aristotle and The Psychology of Aristotle) to the Psychology from an empirical standpoint, in which the concept of intentional in-existence is introduced and fully spelled out—we will follow Brentano’s philosophical path revolving around the core idea that « psychology », rightly understood, is the core discipline of philosophy itself.