There are many ways to respond to Fitch-Church style chains of reasoning. One common strategy is for the anti-realist knowability theorist to adopt an intuitionistic logic. The above version of the proof is valid in intuitionistic logic. But only in classical logic is the negation of empirical humility at (12) equivalent to the omniscience claim that all empirical truths are known: ∀p(Ep→Kp). The anti-realist empirical knowability theorist who adopts an intuitionistic logic could consistently deny that all empirical truths are known while accepting, as she seems forced to by the above proof, that there is no unknown empirical truth. Intuitionism certainly displays a Kantian provenance. And to be on the safe side, I ensure that the other proofs in this paper are also intuitionistically valid. But I will not explore this avenue here. Arguably, the damage has already been done by the time we reach (12). And in any case, I will argue that Kant has a better solution.
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