Fitch's argument purports to show that if all truths are knowable then all truths are known.
The argument exploits the fact that the knowledge predicate or operator is untyped and may thus
apply to sentences containing itself. This article outlines a response to Fitch's argument
based on the idea that knowledge is typed. The first part of the article outlines the
philosophical motivation for the view, comparing it to the motivation behind typing truth. The
second, formal part presents a logic in which knowledge is typed and demonstrates that it
allows nonlogical truths to be knowable yet unknown.
References
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Mathematical Reviews (MathSciNet):
MR934070
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Mathematical Reviews (MathSciNet):
MR986929