THE INTENTIONALITY THESIS

Among Brentano's most important and philosophically influential achievements is his thesis of the intentionality of mind. To say that thought is intentional is to say that it intends or is about something, that it aims at or is directed upon an intended object. Intentionality is thus the aboutness of thought, the relation whereby a psychological state intends or refers to an intended object.

Brentano argues that all psychological phenomena and only psychological phenomena are intentional. He holds that to believe is to believe something; it is for a belief state, a particular kind of mental act, to intend or be about whatever is believed. The intended object of a belief is often a certain state of affairs, that today is Tuesday or that God exists, if the belief is that today is Tuesday or that God exists. The situation is the same with respect to other psychological states, such as desire, hope, fear, doubt, expectation, love, hate. To desire is to desire something, to be directed in thought to the object of desire, whatever the object may happen to be. In what is probably the most famous and undoubtedly most frequently quoted passage of his (1874) Psychologie vom empirischen Standpunkt (Psychology from an Empirical Standpoint), Brentano maintains: