 About the time Kripke named rigidity, Kaplan named the theory of “direct reference” (in “Demonstratives,” eventually published as 1989a: see 1989b, p. 571). As the theory is usually understood, it is the position that the semantic content of a name or other directly referring expression is nothing more than the referent: the referent is all that the name contributes to a proposition expressed by a sentence containing it. So there is no descriptive information semantically conveyed by a directly referring expression. If we think of propositions as “structured entities looking something like the sentences which express them,” as Kaplan invites us to do, we can think of directly referring terms as terms whose contribution to a proposition lacks the structure that characterizes the contribution of definite descriptions. In the case of a definite description, “the constituent of the proposition will be some sort of complex, constructed from various attributes by logical composition. But in the case of a singular term which is directly referential, the constituent of the proposition is just the object itself” (Kaplan 1989a, p. 494; see also the section relating possible worlds and structured propositions in the entry on  structured propositions).