 with \(\Diamond K\varphi\) read as “it is possible to know \(\varphi\)”. In this context, the paradox refers to Fitch’s argument containing an idea conveyed to him in 1945 which shows that, if all truths are knowable, then all truths are already known. As the argument goes, we clearly do not know all truths (as we are not omniscient!); hence, the premise has to be false: not all truths are knowable. The paradox can be summarized by the derivation