Deductive reasoning, used in the Austrian Methodology, leads from true principles (or axioms) to true conclusions. (See description in Deductive Logic.)

Because economic systems consist of living (human) systems, empirical testing becomes generally impossible. Thus, the only way to derive sound economic propositions (or theories) consists of using deductive logic or reasoning.

Only the Austrian School seems to have come to this realization. 

I will delve deeply into the nature and use of deductive logic in the Reason section.