Psychology from an Empirical Standpoint

Brentano's main work, published in 1874 with the first two of a planned six books; the rest never appeared, though Book Two was reissued with new remarks in 1911 and later editors added material from his papers. It aims to make psychology a rigorous science grounded in experience rather than speculation. Book One discusses the method and tasks of psychology and distinguishes inner perception, which gives evident knowledge of our own mental acts, from inner observation, which Brentano thinks impossible. Book Two asks what separates mental from physical phenomena. Its most famous answer is that every mental phenomenon is marked by intentional inexistence, a direction towards an object: in presentation something is presented, in judgement something affirmed or denied, in love or hate something loved or hated. Brentano also argues that every mental act is conscious and aware of itself in passing, and he divides mental phenomena into presentations, judgements, and phenomena of love and hate.

It introduced intentionality, the idea that mental states are about something, into modern philosophy, and so stands behind both phenomenology and much analytic philosophy of mind.