Wittgenstein’s discussion of Gödel in Remarks on the Foundations of Mathematics makes the argument that if someone says of the Gödel sentence, “This proposition is true but unprovable in the system,” we have to ask what exactly is meant by “true.” If “true” simply means “provable in the system,” then calling the sentence true is incorrect, because by construction it is not provable there. But if “true” means something like “correctly describing its own unprovability when we view the system from outside,” then we have already shifted into a different language-game, a meta-level description of the calculus. Wittgenstein’s point is that the philosophical drama arises precisely from sliding between these two uses of “true.”
The key point is that if the Gödel sentence is interpreted as saying “This statement is not provable in the system,” and we can prove that this is indeed the case, then the statement has effectively been proved, but only in a different system. The natural mathematical response is simply to extend the calculus. What philosophers then describe as an eternal “true but unprovable statement” is, from Wittgenstein’s perspective, just a feature of how we choose to organize our formal systems.
So Godel’s comparison between ‘true within the system’ and ‘true but unprovable’ is not like the relation between the provable rules within a language game and the ‘true but unprovable’ hinge making that game intelligible. Rather, it is a relation between two different language games. Assuming the former is to confuse an epistemological and a non-epistemological grammar of truth, which is exactly what Moore did.