Chisholm then says — somewhat cautiously — that a thesis “resembling that of Brentano” may be stated in this way: we can express all of our beliefs about physical phenomena without the use of intentional sentences; but when we describe psychological attitudes, then we must either use intentional sentences or else make use of other terms that are not needed for the description of physical phenomena. In his discussion, it appears that when Chisholm speaks of ‘terms that are not needed for the description of physical phenomena’ he has in mind terms that are ultimately definable only by the use of intentional sentences.