Full Idea
My undecidable arithmetical sentence ...is not at all absolutely undecidable; rather, one can always pass to 'higher' systems in which the sentence in question is decidable.
Gist of Idea
The undecidable sentence can be decided at a 'higher' level in the system
Source
Kurt Gödel (On Formally Undecidable Propositions [1931]), quoted by Peter Koellner - On the Question of Absolute Undecidability 1.1
Book Reference
-: 'Philosophia Mathematica' [-], p.6
A Reaction
[a 1931 MS] He says the reals are 'higher' than the naturals, and the axioms of set theory are higher still. The addition of a truth predicate is part of what makes the sentence become decidable.