AXIOMA (from ἀξίωμα, I am worthy); a self-evident truth, or a proposition whose truth every person perceives at first sight. Thus, that the whole is greater than a part; that a thing cannot be and not be at the same time; and that from nothing, nothing can arise; are axioms.

AXIOM is also an established principle in some art or science. Thus, it is an axiom in physics, that nature does nothing in vain; that effects are proportional to their causes, &c. So it is an axiom in geometry, that things equal to the same thing are also equal to one another; that if to equal things you add equals, the sums will be equal, &c. It is an axiom in optics, that the angle of incidence is equal to the angle of reflection, &c.