Contemporary writers often refer to 'Brentano's Problem' meaning by this the issue of whether all intentional phenomena can be accounted for in terms of a materialist ontology. This, however, was not the problem of intentionaUty which concerned Brentano himself. Rather, the difficulty which he identified is that of how to explain the very contentfulness of mental states, and in particular their apparently relational character. This essay explores something of Brentano's own views on this issue and considers various other recent approaches. (...) It then examines the scholastic doctrine of 'intentional inexistence' in the version associated with Aquinas, according to which content is explained by reference to the occurrence in esse intentionale of the very same features (forms) as contribute to the constitution of extra-mental reality. Various interpretations and aspects of this view are considered and a version of it is commended as providing a plausible solution to Brentano's problem. (shrink)