That's essentially what axioms are. Wether it's reasonable or not depends on your intuition of both axiom & implications. This is where the axiom of choice is

That's essentially what axioms are. Wether it's reasonable or not depends on your intuition of both axiom & implications. This is where the axiom of choice is interesting; many people feel that it seems intuitively reasonable, but the implications are counterintuitive (e.g. banach-tarski)