self-evident truth requiring no proof
"All that lives must die" is a fundamental axiom.
axios (worthy, worth, of like value, weighing as much) (Latin)
Axiom is a rule or principle that most people believe to be true (/universally recognized). See "om" in Axiom which is universally believed Ax +i+om - when the axe is on me I will tell the truth. This is surely evident.