Gödel’s Incompleteness Theorem involves a system’s, such as mathematics, inability to prove itself by utilizing only itself.
The issue is that any logical proof of an axiom will necessarily lead to another which will always merely lead to another endlessly, and thus never complete any absolute proof.
The resolve to this, which was either ignored or merely not realized by those involved in its promotion, is the concern of definitions. Within mathematics, are statements such as “1+1=2”. But how does one prove that 1+1 really does equal 2? Using only mathematics leads to more complex equalities that eventually lead to the proof that 1+1=2. But every one of those depends upon an axiom of some kind presumed to be true. Logic always begins with something presumed to be true such as to deduce what else must be true.
But there is a difference between a common axiom and a definitional axiom. A typical axiom is merely something that most, if not all, people would accept as true. But a definitional axiom is something that is declared to be true throughout the system involved, such as, “2 ≡ 1+1”.
A declared definition for a system cannot be contended with and is not susceptible to truth statement doubts. The definition is a conditional agreement for utilizing the system at all. If the definition is not accepted then the entire system is not accepted. Every system of any nature involved in thought depends on defined concepts that might or might not have been explicated. Any logical proof that leads back to a defined conceptual truth is necessarily true, without exception.
The issue then becomes one of arbitrary definitions and the rationality of the system being proposed. In the case of mathematics, the definitions are hardly arbitrary (being based on simple quantitative counting) and the rationality (meaning the usefulness) has been extremely demonstrated as useful.
Mathematics, whether realized by its proponents or not, is actually based upon Definitional Logic and thus is incontrovertibly true as a system and due to extremely numerous examples, has been empirically demonstrated to be rational.
Anyone contending with mathematics is contending with rationality… and visa-versa.