 Kvanvig (1995) accuses Fitch of a modal fallacy. The fallacy is an illicit substitution into a modal context. Consider a familiar modal fallacy. For all persons \(x\), there is a possible world in which \(x\) is not the inventor of bifocals. (Even Ben Franklin, the actual inventor of bifocals, might not have invented them.) Therefore, there is a possible world in which the inventor of bifocals is not the inventor of bifocals. We can represent the argument formally. Let our quantifiers range over persons, and let ‘\(i\)’ be the non-rigid designator ‘the inventor of bifocals’. Consider the argument: 