   As we saw in section 8, Quine (1960, 220), a leading critic of intentional objects (in the sense of section 7), agrees with Chisholm (1957) that the intentional vocabulary cannot be reduced to some non-intentional vocabulary. Chisholm (1957) took this conclusion to show the correctness of Brentano’s third thesis that intentionality is the mark of the mental. From the same conclusion, Quine (1960, 221) presented an influential dilemma with both epistemological and ontological implications. The first horn of the dilemma is to accept the “indispensability of intentional idioms and the importance of an autonomous science of intention” and to reject a physicalist ontology.  The second horn of the same dilemma is to accept physicalism and renounce the “baselessness” of the intentional idioms and the “emptiness” of a science of intention. This dilemma has been influential in contemporary philosophy of mind.