In Naming and Necessity , Kripke does not talk about propositions and their nature. In the introduction to Naming and Necessity , he even wonders whether the apparatus of propositions might break down if the “better picture” of reference, namely causal reference, is accepted. Further, he writes that he never intended to go so far as to accept the view, sometimes attributed to him, that a sentence that contains the name “Cicero” expresses the same proposition as the corresponding sentence with “Tully” substituted for “Cicero,” the names “Cicero” and “Tully” being coreferential. Instead of focusing on propositions, Kripke suggested that there might be something about sentences that explains failure of substitution of coreferential names. He writes “[that] the English sentence ‘Hesperus is Phosphorus’ could sometimes be used to raise an empirical issue while ‘Hesperus is Hesperus’ could not shows that I do not treat the sentences as completely interchangeable.” 1 This is a curious view, as it clearly indicates that the new account of reference might be incompatible with the then-reigning Fregean view of the nature of propositions and, further, that we might have to focus our attention on sentences rather than propositions.