AXIOMA (from ἀξίωμα, I account worthy), a self-evident truth, or a proposition the truth of which every person perceives at first sight; as, the whole is greater than its part; a thing cannot at the same time be and not be; from nothing nothing can arise. Every science has its particular axioms or elementary principles, which are assumed as the necessary basis of all reasoning. Thus, it is an axiom in physics, that nature does nothing in vain; that effects are proportional to their causes, &c. 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. And it is an axiom in optics, that the angle of incidence is equal to the angle of reflection, &c.