Once it is demonstrated that human action is a necessary attribute of the existence of human beings, the rest of praxeology (and its subdivision, economic theory) consists of the elaboration of the logical implications of the concept of action. Economic analysis is of the form:
(1) Assert A--action axiom.
(2) If A, then B; if B, then C; if C, then D, etc.--by rules of logic.
(3) Therefore, we assert (the truth of) B, C, D, etc.
--Murray N. Rothbard. Man, Economy, and State with Power and Market