This is an explanation of truth vs. proof in model theory and logic. Model theory does not introduce meta-circular inference rules the way logic does; this corresponds to the fact that there is no truth in meta-mathematics, only proof. In order for there to be truth, there must be context axioms; there can be no context axioms in meta-mathematics because meta-mathematics defines what is true and what an axiom is: truth is what can be derived from the axioms according to the inference rules. You could say the inference rules transport knowledge of axioms to knowledge of truth.