axiom

ot noun

1. An established principle in some artistic practice or science that is universally received. The axioms of political economy cannot be considered absolute truths.
2. A seemingly self-evident or necessary truth which is based on assumption; a principle or proposition which cannot actually be proved or disproved.
3. (proof theory) 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).