 Now consider the relevant instance of Fitch’s non-omniscience thesis: \(p \wedge \neg Kp\). Unabbreviated it reads, \(p \wedge \neg \exists x\exists t(Kxpt),\) which says \(p\) is true but nobody ever knows that \(p\). The quantified expression is, on this view, a non-rigid designator. Uttered in the actual world, it is about actual beings and times. But, it is argued, embedded within the scope of a possibility operator the designation varies to be about possible beings and times. When Fitch substituted the true conjunction, \(p \wedge \neg \exists x\exists t(Kxpt),\) for \(p\) in the knowability principle, he substituted for \(p\) a non-rigid designator, thereby altering the reference of the conjunction and perpetrating a modal fallacy.