Full Idea
It is plain that the distinction between object and metalanguage is required for the definability of truth.
Gist of Idea
Any definition of truth requires a metalanguage
Source
Volker Halbach (Axiomatic Theories of Truth [2011], 11)
Book Reference
Halbach,Volker: 'Axiomatic Theories of Truth' [CUP 2011], p.148
A Reaction
Halbach's axiomatic approach has given up on definability, and therefore it can seek to abandon the metalanguage and examine 'type-free' theories.
Related Idea
Idea 16295 Tarski proved that truth cannot be defined from within a given theory [Tarski, by Halbach]