We may now re-express Brentano’s thesis — or a thesis resembling that of Brentano — by reference to intentional sentences. Let us say (1) that we do not need to use intentional sentences when we describe non-psychological phenomena; we can express our beliefs about what is merely ‘physical’ in sentences which are not intentional. But (2) when we wish to describe perceiving, assuming, believing, knowing, wanting, hoping, and other such attitudes, then either (a) we must use sentences which are intentional or (b) we must use terms we do not need to use when we describe non-psychological phenomena.1