axiom

noun3

1. •
   A seemingly self-evident or necessary truth which is based on assumption; a principle or proposition which cannot actually be proved or disproved.

   • Any publicity, runs the axiom, is good publicity. — 1963
2. •
   A fundamental assumption that serves as a basis for deduction of theorems; a postulate (sometimes distinguished from postulates as being universally applicable, whereas postulates are particular to a certain science or context).

   • […] Geometry, an excellent Logic, as you observe, where the definitions are clear, where the Postulata cannot be refused, nor the Axioms denied; […] — 1734
3. •
   An established principle in some artistic practice or science that is universally received.

   • The axioms of political economy cannot be considered absolute truths.