The transition from talk about the intentionality of phenomena to talk about the intentionality of sentences introduces new criteria and considerations which are not to be found in Brentano's original formulation. These are Chisholm's second and third criteria which, by invoking notions of truth and falsity and the notion of linguistic reference, are applicable to sentences rather than to phenomena. The acknowledged source of Chisholm's third criterion — nonsubstitutivity — is Frege's notion of indirect reference: reference to the sense of an expression.