You think it's axiomatic, but I think we need to prove it.

It may be true, but it's hardly axiomatic.

This axiom is unquestionably true.

Cole's Axiom: The sum of the intelligence on the planet is a constant; the population is growing.

Poe's Law is an axiom suggesting that it's difficult, if not impossible, to distinguish between parodies of religious or other fundamentalism and its genuine proponents, since they both seem equally insane.

In America it's taken as axiomatic that only children can learn languages.