  One standard sort of argument for propositions is metalinguistic. Thus, many argue that we think of that-clauses as designating expressions if we are to explain how certain argument patterns (such as those considered in Section 2) are valid and in fact have sound instances (Horwich 1990, Higginbotham 1991, Schiffer 1996, Bealer 1998). Since some of these sound argument instances contain as premises sentences attributing truth to the designata of that-clauses, those designata must be bearers of truth-values.  Similarly, premises of some of these sound instances ascribe attitudes toward the designatum of a that-clauses, these designata would seem to be objects of attitudes.  In brief, in order to explain these facts about validity and soundness, it seems that-clauses must not only designate but must designate entities fitting the propositional role. 