What follows is an investigation of the ontology of Franz Brentano with special reference to Brentano's later and superficially somewhat peculiar doctrine to the effect that the substances of the material world are three dimensional places. Taken as a whole, Brentano's philosophy is marked by three, not obviously compatible, trait. In the first place, his work is rooted in the metaphysics of Aristotle, above all in Aristotle's substance/accident ontology and in the Aristotelian theory of categories. In the second place, Brentano (...) embraced a Cartesian epistemology. He saw the source of all knowledge as residing in our direct awareness of our own mental phenomena and in our capacity to grasp evident incompatibilities in the realm of concepts.) Thirdly, he regarded the existence of an external world as at most probable, and denied outright the existence of a world similar to the world that is given in experience. Finally, and in some sense linking together these opposing strands, he propagated an idea of what he called "descriptive psychology", a discipline which would on the one hand yield exact knowledge of the structures and categories of mental life, and on the other hand provide an epistemologically sure foundation for other branches of philosophy. As we shall see, it is this psychological aspect of Brentano's philosophy which leads him to his conception of the substantiality of place. Surprisingly, however, the psychological considerations which underlie Brentano's thinking will be shown to raise a series of questions strictly ontological in nature, questions which are not without a systematic interest of their own. (shrink)