Gillian Russell
Washington University-St. Louis

By an implication barrier thesis I shall mean a claim which says that no set containing only sentences of one kind entails a sentence of another kind, for example, the claim that no set containing only descriptive sentences entails a normative sentence, or the claim that no set containing only particular sentences entails a universal one. The aim of the present paper is to formulate and prove an indexical barrier theorem, according to which (extremely roughly) no set containing only non-indexical sentences entails an indexical sentence. Though a number of obstacles to the proof of such a theorem exist, the thought that there is some non-trivial theorem to be discovered is motivated by well-known thought experiments from the philosophies of language and mind, such as those of Hector-Neri Casteneda, John Perry and David Lewis.