self-evident truth; obvious fact; truism; axiom
A formal or logical expression for something so clear it needs no proof. Often used in philosophical, mathematical, or argumentative contexts.
It is a self-evident truth that all people are born equal.
In mathematics, theorems are derived from a few axioms.
Compound of 自明 (self-evident) + の (possessive particle) + 理 (reason, principle). The phrase is a calque from Western philosophical terminology, likely entering Japanese during the Meiji period.