Overview#Paradox of Knowability really "Fitch's paradox of knowability"" is one of the fundamental puzzles of epistemic logic.
Paradox of Knowability provides a challenge to the knowability thesis, which states that every truth is, in principle, knowable.
The paradox is that this assumption implies the omniscience principle, which asserts that every truth is known.
Essentially, Fitch's paradox asserts that the existence of an unknown truth is unknowable.
So if all truths were knowable, it would follow that all truths are in fact known."