Chisholm on Brentano's thesis
Roderick Chisholm provides, in different places, two formulations of Brentano's thesis about the relation between the psychological and the intentional: (1) all and only psychological sentences are intentional; (2) no psychological intentional sentence is equivalent to a nonintentional sentence. Chisholm also presents several definitions of intentionality. Some of these allow that a sentence is intentional while its negation is nonintentional, which ruins the prospects of defending the more plausible and interesting thesis (2). A generalization of the notion of logical independence to any number of mutually independent sentences permits a revision of Chisholm's criteria of intentionality that ensures that a sentence is intentional on a criterion exactly when its negation is as well.