 In order to make clear the second motivation for abandoning the view of propositions as sets of worlds and adopting the structured proposition account, we must discuss the notions of rigid designation and direct reference. A rigid designator is an expression that designates the same individual in all possible circumstances or worlds. In the early 1970’s, Saul Kripke argued in Naming and Necessity that ordinary proper names are rigid designators. Kripke claimed that when we consider a sentence containing an ordinary proper name, such as